commit 3087975833e4d435f7b95dc7e56b4b3d705c068a
Author: Mark Poliakov <mark@alnyan.me>
Date:   Wed Sep 3 14:56:28 2025 +0300

    Initial commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..38e8f3b
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+/obj_dir
+/*.log
+/log
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..357be16
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,33 @@
+SRC_ALL=$(wildcard src/**/*.sv)
+SRC_MODULE=$(filter-out %_top.sv,$(filter-out %_tb.sv,$(SRC_ALL)))
+DEF_MODULE=$(wildcard src/*.svh)
+
+FIRMWARE_SRC=firmware/src/entry.S \
+			 firmware/src/main.rs \
+			 firmware/link.ld \
+			 firmware/Cargo.toml
+
+MAIN_TOP=src/rvx0_soc_top.sv
+
+all: obj_dir/rvx0
+
+obj_dir/apb0_memory.hex: obj_dir/firmware.bin tool/makebin.py
+	./tool/makebin.py obj_dir/firmware.bin $@
+
+obj_dir/firmware.bin: firmware/target/riscv32i-unknown-none-elf/release/firmware
+	llvm-objcopy -O binary $< $@
+
+firmware/target/riscv32i-unknown-none-elf/release/firmware: $(FIRMWARE_SRC)
+	cd firmware && cargo build --release
+
+obj_dir/rvx0: $(SRC_MODULE) $(DEF_MODULE) $(MAIN_TOP) obj_dir/apb0_memory.hex
+	mkdir -p obj_dir
+	verilator --assert --binary -Isrc -o rvx0 $(MAIN_TOP) $(SRC_MODULE)
+#
+# obj_dir/firmware.elf: $(FIRMWARE_OBJ) src/firmware.ld
+#
+# obj_dir/apb0_memory.hex: src/apb0_memory.S tool/makebin.py
+# 	mkdir -p obj_dir
+# 	riscv64-elf-gcc -c -o obj_dir/apb0_memory.o src/apb0_memory.S
+# 	llvm-objcopy -O binary obj_dir/apb0_memory.o obj_dir/apb0_memory.bin
+# 	./tool/makebin.py obj_dir/apb0_memory.bin $@
diff --git a/firmware/.cargo/config.toml b/firmware/.cargo/config.toml
new file mode 100644
index 0000000..17ca093
--- /dev/null
+++ b/firmware/.cargo/config.toml
@@ -0,0 +1,6 @@
+[target.riscv32i-unknown-none-elf]
+rustflags = ["-Clink-arg=-Tlink.ld"]
+[build]
+target = "riscv32i-unknown-none-elf"
+[unstable]
+build-std = ["core"]
diff --git a/firmware/.gitignore b/firmware/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/firmware/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/firmware/Cargo.lock b/firmware/Cargo.lock
new file mode 100644
index 0000000..a50f075
--- /dev/null
+++ b/firmware/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "firmware"
+version = "0.1.0"
diff --git a/firmware/Cargo.toml b/firmware/Cargo.toml
new file mode 100644
index 0000000..678580a
--- /dev/null
+++ b/firmware/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "firmware"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/firmware/link.ld b/firmware/link.ld
new file mode 100644
index 0000000..79cecd1
--- /dev/null
+++ b/firmware/link.ld
@@ -0,0 +1,35 @@
+ENTRY(__entry);
+
+SECTIONS {
+    . = 0x1000;
+
+    .text : {
+        *(.text.entry)
+        *(.text*)
+    }
+
+    . = ALIGN(4);
+
+    .rodata : {
+        *(.rodata*)
+        . = ALIGN(4);
+    }
+
+    . = 0x20000;
+
+    .vectors : {
+        *(.text.vectors)
+    }
+
+    . = 0x20000000;
+
+    .data : {
+        *(.data*)
+    }
+
+    . = ALIGN(16);
+
+    .bss : {
+        *(.bss*)
+    }
+}
diff --git a/firmware/src/entry.S b/firmware/src/entry.S
new file mode 100644
index 0000000..cb18f62
--- /dev/null
+++ b/firmware/src/entry.S
@@ -0,0 +1,22 @@
+.global __entry
+
+.pushsection .text.entry
+.option push
+.option norvc
+__entry:
+    la sp, stack_top
+    jal {firmware_main}
+
+.option pop
+.popsection // .text.entry
+
+.pushsection .text.vectors
+__vector:
+    j .
+.popsection // .text.vectors
+
+.pushsection .bss
+stack_bottom:
+    .skip 2048
+stack_top:
+.popsection // .bss
diff --git a/firmware/src/main.rs b/firmware/src/main.rs
new file mode 100644
index 0000000..a8b2587
--- /dev/null
+++ b/firmware/src/main.rs
@@ -0,0 +1,42 @@
+#![allow(unsafe_op_in_unsafe_fn)]
+#![no_std]
+#![no_main]
+
+use core::{arch::global_asm, fmt, panic::PanicInfo};
+
+#[panic_handler]
+fn panic_handler(_pi: &PanicInfo) -> ! {
+    loop {}
+}
+
+struct D;
+
+const DEBUG_BASE: usize = 0x1000_0000;
+
+impl fmt::Write for D {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        let ptr: *mut u32 = core::ptr::with_exposed_provenance_mut(DEBUG_BASE);
+        for byte in s.bytes() {
+            unsafe { ptr.write_volatile(byte as u32) };
+        }
+        Ok(())
+    }
+}
+
+unsafe extern "C" fn firmware_main() -> ! {
+    use fmt::Write;
+
+    let mut d = D;
+    for i in 0..10 {
+        write!(d, "Hello {i}").ok();
+        write!(d, "\n").ok();
+    }
+
+    loop {
+        // TODO pause/system/fence instruction not implemented
+        // core::hint::spin_loop();
+        core::arch::asm!("nop");
+    }
+}
+
+global_asm!(include_str!("entry.S"), firmware_main = sym firmware_main);
diff --git a/src/core/rvx0_alu.sv b/src/core/rvx0_alu.sv
new file mode 100644
index 0000000..4521f27
--- /dev/null
+++ b/src/core/rvx0_alu.sv
@@ -0,0 +1,40 @@
+module rvx0_alu (
+    input wire [3:0]    aluop_i,
+    input wire [31:0]   value1_i,
+    input wire [31:0]   value2_i,
+    input wire [31:0]   imm_i,
+
+    output logic [31:0] output_o
+);
+
+wire [31:0] value1;
+wire [31:0] value2;
+wire [4:0] value2_lo;
+
+wire signed [31:0] value1_signed;
+wire signed [31:0] value2_signed;
+
+assign value1 = value1_i;
+assign value2 = value2_i + imm_i;
+
+assign value1_signed = value1;
+assign value2_signed = value2;
+
+assign value2_lo = value2[4:0];
+
+always_comb begin
+    case (aluop_i)
+    ALUOP_ADD: output_o = value1 + value2;
+    ALUOP_SLL: output_o = value1 << value2_lo;
+    ALUOP_SLT: output_o = 32'(value1_signed < value2_signed);
+    ALUOP_SLTU: output_o = 32'(value1 < value2);
+    ALUOP_XOR: output_o = value1 ^ value2;
+    ALUOP_SRL: output_o = value1 >> value2_lo;
+    ALUOP_OR: output_o = value1 | value2;
+    ALUOP_AND: output_o = value1 & value2;
+    ALUOP_SUB: output_o = value1 - value2;
+    ALUOP_SRA: output_o = value1 >>> value2_lo;
+    endcase
+end
+
+endmodule
diff --git a/src/core/rvx0_brancher.sv b/src/core/rvx0_brancher.sv
new file mode 100644
index 0000000..9bf0b38
--- /dev/null
+++ b/src/core/rvx0_brancher.sv
@@ -0,0 +1,28 @@
+`include "rvx0_defs.svh"
+
+module rvx0_brancher (
+    input wire [31:0]   rs1_value_i,
+    input wire [31:0]   rs2_value_i,
+
+    input wire [2:0]    funct3_i,
+
+    output logic        branch_taken_o
+);
+    wire signed [31:0] rs1_value_signed;
+    wire signed [31:0] rs2_value_signed;
+
+    assign rs1_value_signed = rs1_value_i;
+    assign rs2_value_signed = rs2_value_i;
+
+    always_comb begin
+        case (funct3_i)
+        COND_EQ: branch_taken_o = rs1_value_i == rs2_value_i;
+        COND_NE: branch_taken_o = rs1_value_i != rs2_value_i;
+        COND_LT: branch_taken_o = rs1_value_signed < rs2_value_signed;
+        COND_GE: branch_taken_o = rs1_value_signed >= rs2_value_signed;
+        COND_LTU: branch_taken_o = rs1_value_i < rs2_value_i;
+        COND_GEU: branch_taken_o = rs1_value_i >= rs2_value_i;
+        default: branch_taken_o = 0;
+        endcase
+    end
+endmodule
diff --git a/src/core/rvx0_control.sv b/src/core/rvx0_control.sv
new file mode 100644
index 0000000..1837155
--- /dev/null
+++ b/src/core/rvx0_control.sv
@@ -0,0 +1,133 @@
+`include "rvx0_defs.svh"
+
+module rvx0_control (
+    input wire clk_i,
+    input wire rst_i,
+
+    input wire need_memory_read_i,
+    input wire need_memory_write_i,
+    input wire exec_stall_i,
+    input wire exec_ready_i,
+
+    input wire instruction_fault_i,
+    input wire intr_ext_i,
+
+    input wire [31:0]   memory_address_i,
+    input wire [31:0]   memory_write_i,
+    input wire [31:0]   pc_value_i,
+
+    rvx0_apb.master apb_master,
+
+    output reg [1:0]    control_state_o,
+    output reg [31:0]   instruction_o,
+    output reg [31:0]   memory_read_o,
+
+    output reg          fault_instruction_align_o,
+    output reg          fault_instruction_fetch_o,
+    output reg          fault_memory_access_o
+);
+
+    always @(posedge clk_i) begin
+        if (rst_i) begin
+            control_state_o <= CSTATE_FETCH;
+        end
+    end
+
+    // TODO handle pslverr
+    always @(negedge clk_i) begin
+        if (~rst_i) begin
+            case (control_state_o)
+            CSTATE_FETCH: begin
+                fault_instruction_fetch_o <= 0;
+                fault_instruction_align_o <= 0;
+
+                if (intr_ext_i) begin
+                    control_state_o <= CSTATE_EXEC;
+                    instruction_o <= 0;
+                end else if (pc_value_i[1:0] != 0) begin
+                    fault_instruction_align_o <= 1;
+                    instruction_o <= 0;
+
+                    control_state_o <= CSTATE_EXEC;
+                end else begin
+                    apb_master.paddr <= pc_value_i;
+                    apb_master.pwrite <= 0;
+                    apb_master.penable <= 1;
+
+                    if (apb_master.pslverr) begin
+                        instruction_o <= 0;
+                        fault_instruction_fetch_o <= 1;
+
+                        apb_master.penable <= 0;
+
+                        control_state_o <= CSTATE_EXEC;
+                    end else if (apb_master.pready) begin
+                        instruction_o <= apb_master.prdata;
+                        apb_master.penable <= 0;
+
+                        control_state_o <= CSTATE_READ;
+                    end
+                end
+            end
+            CSTATE_READ: begin
+                fault_memory_access_o <= 0;
+
+                if (intr_ext_i) begin
+                    control_state_o <= CSTATE_EXEC;
+                end else if (~need_memory_read_i || instruction_fault_i) begin
+                    control_state_o <= CSTATE_EXEC;
+                end else begin
+                    apb_master.paddr <= memory_address_i;
+                    apb_master.pwrite <= 0;
+                    apb_master.penable <= 1;
+
+                    if (apb_master.pslverr) begin
+                        memory_read_o <= 0;
+                        apb_master.penable <= 0;
+
+                        fault_memory_access_o <= 1;
+
+                        control_state_o <= CSTATE_EXEC;
+                    end else if (apb_master.pready) begin
+                        memory_read_o <= apb_master.prdata;
+                        apb_master.penable <= 0;
+
+                        control_state_o <= CSTATE_EXEC;
+                    end
+                end
+            end
+            CSTATE_EXEC: begin
+                if (exec_stall_i) begin
+                    $display("control: exec_stall_i @ %x", pc_value_i);
+                    control_state_o <= CSTATE_FETCH;
+                end else if (exec_ready_i) begin
+                    control_state_o <= CSTATE_WRITE;
+                end
+            end
+            CSTATE_WRITE: begin
+                fault_memory_access_o <= 0;
+
+                if (~need_memory_write_i) begin
+                    control_state_o <= CSTATE_FETCH;
+                end else begin
+                    apb_master.paddr <= memory_address_i;
+                    apb_master.pwdata <= memory_write_i;
+                    apb_master.pwrite <= 1;
+                    apb_master.penable <= 1;
+
+                    $display("WRITE %x -> %x", memory_write_i, memory_address_i);
+
+                    if (apb_master.pslverr) begin
+                        apb_master.penable <= 0;
+                        fault_memory_access_o <= 1;
+                        control_state_o <= CSTATE_EXEC;
+                    end else if (apb_master.pready) begin
+                        apb_master.penable <= 0;
+                        control_state_o <= CSTATE_FETCH;
+                    end
+                end
+            end
+            endcase
+        end
+    end
+endmodule
diff --git a/src/core/rvx0_core.sv b/src/core/rvx0_core.sv
new file mode 100644
index 0000000..e176b15
--- /dev/null
+++ b/src/core/rvx0_core.sv
@@ -0,0 +1,301 @@
+/* verilator lint_off PINMISSING */
+/* verilator lint_off MULTIDRIVEN */
+
+`include "rvx0_defs.svh"
+
+module rvx0_core #(
+    parameter RESET_VECTOR
+) (
+    input wire clk_i,
+    input wire rst_i,
+
+    input wire intr_ext_i,
+
+    rvx0_apb.master apb_master
+);
+    wire [31:0]     pc_value;
+    logic [31:0]    pc_write_value;
+    wire            fault;
+
+    // CSRs
+
+    wire [31:0]     csr_mtvec;
+    wire [31:0]     csr_mepc;
+
+    // Exception generation
+
+    logic [31:0]    mcause_write_value;
+    logic [31:0]    mepc_write_value;
+    logic [31:0]    mtval_write_value;
+
+    // Faults
+
+    wire            fault_memory_align;
+    wire            fault_instruction;
+    wire            fault_instruction_align;
+    wire            fault_instruction_fetch;
+    wire            fault_memory_access;
+
+    // Generated faults
+    wire            fault_instruction_decode;
+    wire            fault_unsupported_size;
+    wire            fault_address_align;
+
+    // Control
+
+    wire            need_memory_read;
+    wire            need_memory_write;
+    logic           exec_ready;
+    logic           exec_stall;
+    wire [1:0]      control_state;
+    wire [31:0]     instruction;
+    wire            state_exec;
+
+    // Regfile/control
+
+    wire [31:0]     rs1_value;
+    wire [31:0]     rs2_value;
+    logic [31:0]    rd_write_value;
+
+    // Decoder
+
+    wire            conditional;
+    wire [4:0]      rs1;
+    wire [4:0]      rs2;
+    wire [4:0]      rd;
+    wire            v1src;
+    wire [1:0]      v2src;
+    wire [1:0]      vdsrc;
+    wire [31:0]     imm;
+    wire [3:0]      aluop;
+    wire            write_pc;
+    wire [2:0]      funct3;
+
+    // Into ALU
+
+    wire [31:0]     alu_value1;
+    logic [31:0]    alu_value2;
+    wire [31:0]     alu_output;
+
+    // Branch unit
+
+    wire            write_pc_and_taken;
+    wire            branch_taken;
+    wire            write_rd;
+    wire            pc_clk;
+
+    // Memword
+
+    wire [31:0] memory_read_input;
+    wire [31:0] memory_read_output;
+    wire [31:0] memory_write_input;
+    wire [31:0] memory_write_output;
+    wire        memory_access_partial;
+
+    rvx0_pc #(
+        .RESET_VECTOR               (RESET_VECTOR)
+    ) pc (
+        .rst_i                      (rst_i),
+        .clk_i                      (pc_clk),
+        .pc_value_i                 (pc_write_value),
+        .write_pc_i                 (write_pc_and_taken),
+        .pc_value_o                 (pc_value)
+    );
+
+    rvx0_brancher brancher (
+        .rs1_value_i                (rs1_value),
+        .rs2_value_i                (rs2_value),
+        .funct3_i                   (funct3),
+        .branch_taken_o             (branch_taken)
+    );
+
+    rvx0_decoder decoder (
+        .instruction_i              (instruction),
+
+        .v1src_o                    (v1src),
+        .v2src_o                    (v2src),
+        .vdsrc_o                    (vdsrc),
+        .rs1_o                      (rs1),
+        .rs2_o                      (rs2),
+        .rd_o                       (rd),
+        .imm_o                      (imm),
+        .aluop_o                    (aluop),
+        .write_mem_o                (need_memory_write),
+        .write_pc_o                 (write_pc),
+        .funct3_o                   (funct3),
+        .instruction_fault_o        (fault_instruction_decode),
+        .conditional_o              (conditional)
+    );
+
+    rvx0_regfile regfile (
+        .clk_i                      (clk_i),
+        .rst_i                      (rst_i),
+
+        .rs1_i                      (rs1),
+        .rs2_i                      (rs2),
+        .rd_i                       (rd),
+        .write_value_i              (rd_write_value),
+        .rd_write_i                 (write_rd),
+
+        .rs1_o                      (rs1_value),
+        .rs2_o                      (rs2_value)
+    );
+
+    rvx0_alu alu (
+        .aluop_i                    (aluop),
+        .value1_i                   (alu_value1),
+        .value2_i                   (alu_value2),
+        .imm_i                      (imm),
+        .output_o                   (alu_output)
+    );
+
+    // Control
+
+    rvx0_control control (
+        .clk_i                      (clk_i),
+        .rst_i                      (rst_i),
+        .apb_master                 (apb_master),
+        .control_state_o            (control_state),
+        .instruction_o              (instruction),
+        .instruction_fault_i        (fault_instruction),
+        .pc_value_i                 (pc_value),
+        .memory_address_i           (alu_output),
+        .need_memory_read_i         (need_memory_read),
+        .need_memory_write_i        (need_memory_write),
+        .exec_ready_i               (exec_ready),
+        .exec_stall_i               (exec_stall),
+        .memory_read_o              (memory_read_input),
+        .memory_write_i             (memory_write_output),
+        .fault_instruction_align_o  (fault_instruction_align),
+        .fault_instruction_fetch_o  (fault_instruction_fetch),
+        .fault_memory_access_o      (fault_memory_access)
+    );
+
+    rvx0_memword memword (
+        .memory_read_i              (memory_read_input),
+        .memory_write_i             (memory_write_input),
+        .memory_address_i           (alu_output),
+
+        .funct3_i                   (funct3),
+
+        .memory_read_o              (memory_read_output),
+        .memory_write_o             (memory_write_output),
+        .memory_access_partial_o    (memory_access_partial),
+        .alignment_fault_o          (fault_address_align),
+        .unsupported_size_fault_o   (fault_unsupported_size)
+    );
+
+    rvx0_csr csr (
+        .clk_i                      (clk_i),
+        .rst_i                      (rst_i),
+
+        .mepc_i                     (mepc_write_value),
+        .mepc_write_i               (fault),
+        .mcause_i                   (mcause_write_value),
+        .mcause_write_i             (fault),
+        .mtval_i                    (mtval_write_value),
+        .mtval_write_i              (fault),
+
+        .mtvec_o                    (csr_mtvec)
+    );
+
+    assign fault = fault_instruction_align ||
+                   fault_instruction_fetch ||
+                   fault_instruction ||
+                   fault_memory_align ||
+                   fault_memory_access ||
+                   intr_ext_i;
+
+    assign fault_instruction = fault_instruction_decode || (fault_unsupported_size && (need_memory_read || need_memory_write));
+    assign fault_memory_align = fault_address_align && (need_memory_write || need_memory_read);
+
+    assign memory_write_input = rs2_value;
+
+    assign need_memory_read = (vdsrc == RDSRC_MEM) || (need_memory_write && memory_access_partial);
+    assign alu_value1 = v1src == V1SRC_ZERO ? 0 : rs1_value;
+    assign state_exec = control_state == CSTATE_EXEC;
+
+    assign pc_clk = (state_exec || rst_i) && clk_i;
+
+    assign write_rd = (vdsrc != RDSRC_NONE) && state_exec && ~fault;
+
+    assign write_pc_and_taken = ((conditional ? branch_taken : 1) && write_pc) || fault;
+
+    // Value mux
+    always_comb begin
+        case (vdsrc)
+        RDSRC_PC:   rd_write_value = pc_value + 4;
+        RDSRC_ALU:  rd_write_value = alu_output;
+        RDSRC_MEM:  rd_write_value = memory_read_output;
+        RDSRC_NONE: rd_write_value = 0;
+        endcase
+
+        case (v2src)
+        V2SRC_ZERO: alu_value2 = 0;
+        V2SRC_PC:   alu_value2 = pc_value;
+        V2SRC_RS2:  alu_value2 = rs2_value;
+        endcase
+
+        if (fault) begin
+            pc_write_value = csr_mtvec;
+        end else begin
+            pc_write_value = alu_output;
+        end
+    end
+
+    // Exception parameter encoding
+    always_comb begin
+        mcause_write_value = 0;
+        mtval_write_value = 0;
+        mepc_write_value = pc_value;
+
+        if (fault_instruction_align) begin
+            mcause_write_value = MCAUSE_INSTRUCTION_ADDRESS_MISALIGN;
+        end else if (fault_instruction_fetch) begin
+            mcause_write_value = MCAUSE_INSTRUCTION_ACCESS_FAULT;
+            mtval_write_value = pc_value;
+        end else if (fault_instruction) begin
+            mcause_write_value = MCAUSE_ILLEGAL_INSTRUCTION;
+            mtval_write_value = instruction;
+        end else if (~need_memory_write && fault_memory_align) begin
+            mcause_write_value = MCAUSE_LOAD_ADDRESS_MISALIGNED;
+            mtval_write_value = alu_output;
+        end else if (~need_memory_write && fault_memory_access) begin
+            mcause_write_value = MCAUSE_LOAD_ACCESS_FAULT;
+        end else if (fault_memory_align) begin
+            mcause_write_value = MCAUSE_STORE_ADDRESS_MISALIGNED;
+            mtval_write_value = alu_output;
+        end else if (fault_memory_access) begin
+            mcause_write_value = MCAUSE_STORE_ACCESS_FAULT;
+            // Because this happens at write pipeline stage and PC has already
+            // been incremented
+            mepc_write_value = pc_value - 4;
+            mtval_write_value = alu_output;
+        end else if (intr_ext_i) begin
+            mcause_write_value = MCAUSE_INTR_EXT_MMODE | MCAUSE_INTERRUPT;
+        end
+    end
+
+    always @(posedge clk_i) begin
+        case (control_state)
+        CSTATE_EXEC: begin
+            exec_ready = 0;
+            exec_stall = 0;
+
+            if (fault) begin
+                $display("Take exception mcause=%x, mepc=%x, mtval=%x to %x", mcause_write_value, mepc_write_value, mtval_write_value, csr_mtvec);
+                regfile.dump_state;
+                $finish;
+                exec_stall = 1;
+            end else begin
+`ifdef RVX0_DEBUGGING
+                $display("[%x] %x, rs1 (r%d)=%x, rs2 (r%d)=%x, v1src=%d, v2src=%d, vdsrc=%d", pc_value, instruction, rs1, rs1_value, rs2, rs2_value, v1src, v2src, vdsrc);
+                $display("\talu_value1=%x, alu_value2=%x, imm=%x, rd_write_value=%x", alu_value1, alu_value2, imm, rd_write_value);
+                $display("\tmri=%x, mro=%x, mwi=%x, mwo=%x", memory_read_input, memory_read_output, memory_write_input, memory_write_output);
+`endif
+                exec_ready = 1;
+            end
+        end
+        endcase
+    end
+endmodule
diff --git a/src/core/rvx0_csr.sv b/src/core/rvx0_csr.sv
new file mode 100644
index 0000000..4a85208
--- /dev/null
+++ b/src/core/rvx0_csr.sv
@@ -0,0 +1,52 @@
+// TODO Zicsr
+module rvx0_csr (
+    input wire clk_i,
+    input wire rst_i,
+
+    input wire [31:0]   mepc_i,
+    input wire [31:0]   mcause_i,
+    input wire [31:0]   mtval_i,
+
+    input wire          mepc_write_i,
+    input wire          mcause_write_i,
+    input wire          mtval_write_i,
+
+    output wire [31:0]  misa_o,         // Hardwired
+    output wire [31:0]  mvendorid_o,    // Hardwired
+    output wire [31:0]  marchid_o,      // Hardwired
+    output wire [31:0]  mimpid_o,       // Hardwired
+    output wire [31:0]  mhartid_o,      // Hardwired
+    output reg [31:0]   mstatus_o,      // TODO
+    output reg [31:0]   mstatush_o,     // TODO
+    output reg [31:0]   mtvec_o,
+    output reg [31:0]   mepc_o,
+    output reg [31:0]   mcause_o,
+    output reg [31:0]   mtval_o         // TODO
+);
+    // Add extensions here :)
+    assign misa_o       = MISA_MXLEN_32;
+    assign mvendorid_o  = 0;
+    assign marchid_o    = 0;
+    assign mimpid_o     = 0;
+    assign mhartid_o    = 0;
+
+    always @(posedge clk_i) begin
+        if (rst_i) begin
+            // TODO set from CPU
+            mtvec_o = 'h00020000;
+            mepc_o = 0;
+            mstatus_o = 0;
+            mstatush_o = 0;
+        end
+
+        if (mepc_write_i) begin
+            mepc_o <= mepc_i;
+        end
+        if (mcause_write_i) begin
+            mcause_o <= mcause_i;
+        end
+        if (mtval_write_i) begin
+            mtval_o <= mtval_i;
+        end
+    end
+endmodule
diff --git a/src/core/rvx0_memword.sv b/src/core/rvx0_memword.sv
new file mode 100644
index 0000000..1f547bc
--- /dev/null
+++ b/src/core/rvx0_memword.sv
@@ -0,0 +1,70 @@
+module rvx0_memword (
+    input wire [31:0]   memory_read_i,
+    input wire [31:0]   memory_write_i,
+    input wire [31:0]   memory_address_i,
+
+    input wire [2:0]    funct3_i,
+
+    output logic [31:0] memory_write_o,
+    output logic [31:0] memory_read_o,
+    output wire         memory_access_partial_o,
+    output logic        alignment_fault_o,
+    output logic        unsupported_size_fault_o
+);
+    wire                sign_extend;
+    wire [4:0]          shift;
+    wire signed [31:0]  memory_read_signed;
+    wire [31:0]         wmask_8b;
+    wire [31:0]         wmask_16b;
+    logic [31:0]        memory_read_unsigned;
+
+    assign sign_extend = ~funct3_i[2];
+    assign shift = memory_address_i[1:0] << 3;
+
+    assign memory_access_partial_o = funct3_i[1:0] != 2'b10;
+    assign memory_read_signed = memory_read_unsigned;
+
+    assign wmask_8b = 32'hFF << shift;
+    assign wmask_16b = 32'hFFFF << shift;
+
+    always_comb begin
+        memory_read_unsigned = 0;
+        memory_write_o = 0;
+        alignment_fault_o = 0;
+        unsupported_size_fault_o = 0;
+
+        case (funct3_i[1:0])
+        2'b00: begin
+            memory_read_unsigned = (memory_read_i >> shift) & 32'hFF;
+
+            memory_write_o = (memory_read_i & ~wmask_8b) | ((memory_write_i & 32'hFF) << shift);
+        end
+        2'b01: begin
+            memory_read_unsigned = (memory_read_i >> shift) & 32'hFFFF;
+
+            memory_write_o = (memory_read_i & ~wmask_16b) | ((memory_write_i & 32'hFFFF) << shift);
+
+            if (memory_address_i[0] != 0) begin
+                alignment_fault_o = 1;
+            end
+        end
+        2'b10: begin
+            memory_read_unsigned = memory_read_i;
+            memory_write_o = memory_write_i;
+
+            if (memory_address_i[1:0] != 0) begin
+                alignment_fault_o = 1;
+            end
+        end
+        2'b11: begin
+            unsupported_size_fault_o = 1;
+        end
+        endcase
+
+        if (sign_extend) begin
+            memory_read_o = memory_read_signed;
+        end else begin
+            memory_read_o = memory_read_unsigned;
+        end
+    end
+endmodule
diff --git a/src/core/rvx0_pc.sv b/src/core/rvx0_pc.sv
new file mode 100644
index 0000000..67389a5
--- /dev/null
+++ b/src/core/rvx0_pc.sv
@@ -0,0 +1,20 @@
+module rvx0_pc #(
+    parameter logic [31:0] RESET_VECTOR
+) (
+    input wire clk_i,
+    input wire rst_i,
+    input wire write_pc_i,
+    input wire [31:0] pc_value_i,
+
+    output reg [31:0] pc_value_o
+);
+    always @(posedge clk_i) begin
+        if (rst_i) begin
+            pc_value_o <= RESET_VECTOR;
+        end else if (write_pc_i) begin
+            pc_value_o <= pc_value_i;
+        end else begin
+            pc_value_o <= pc_value_o + 4;
+        end
+    end
+endmodule
diff --git a/src/core/rvx0_regfile.sv b/src/core/rvx0_regfile.sv
new file mode 100644
index 0000000..66f2a6f
--- /dev/null
+++ b/src/core/rvx0_regfile.sv
@@ -0,0 +1,108 @@
+module rvx0_regfile (
+    input wire clk_i,
+    input wire rst_i,
+
+    input wire [4:0] rs1_i,
+    input wire [4:0] rs2_i,
+    input wire [4:0] rd_i,
+
+    input wire [31:0] write_value_i,
+    input wire rd_write_i,
+
+    output wire [31:0] rs1_o,
+    output wire [31:0] rs2_o
+);
+    // Debugger friendly names
+    wire [31:0] ra;
+    wire [31:0] sp;
+    wire [31:0] gp;
+    wire [31:0] tp;
+    wire [31:0] t0;
+    wire [31:0] t1;
+    wire [31:0] t2;
+    wire [31:0] s0;
+    wire [31:0] s1;
+    wire [31:0] a0;
+    wire [31:0] a1;
+    wire [31:0] a2;
+    wire [31:0] a3;
+    wire [31:0] a4;
+    wire [31:0] a5;
+    wire [31:0] a6;
+    wire [31:0] a7;
+    wire [31:0] s2;
+    wire [31:0] s3;
+    wire [31:0] s4;
+    wire [31:0] s5;
+    wire [31:0] s6;
+    wire [31:0] s7;
+    wire [31:0] s8;
+    wire [31:0] s9;
+    wire [31:0] s10;
+    wire [31:0] s11;
+    wire [31:0] t3;
+    wire [31:0] t4;
+    wire [31:0] t5;
+    wire [31:0] t6;
+
+    assign ra = regs[0];
+    assign sp = regs[1];
+    assign gp = regs[2];
+    assign tp = regs[3];
+    assign t0 = regs[4];
+    assign t1 = regs[5];
+    assign t2 = regs[6];
+    assign s0 = regs[7];
+    assign s1 = regs[8];
+    assign a0 = regs[9];
+    assign a1 = regs[10];
+    assign a2 = regs[11];
+    assign a3 = regs[12];
+    assign a4 = regs[13];
+    assign a5 = regs[14];
+    assign a6 = regs[15];
+    assign a7 = regs[16];
+    assign s2 = regs[17];
+    assign s3 = regs[18];
+    assign s4 = regs[19];
+    assign s5 = regs[20];
+    assign s6 = regs[21];
+    assign s7 = regs[22];
+    assign s8 = regs[23];
+    assign s9 = regs[24];
+    assign s10 = regs[25];
+    assign s11 = regs[26];
+    assign t3 = regs[27];
+    assign t4 = regs[28];
+    assign t5 = regs[29];
+    assign t6 = regs[30];
+
+    function void dump_state;
+        $display("ra=%x  sp=%x  gp=%x  tp=%x", ra, sp, gp, tp);
+        $display("t0=%x  t1=%x  t2=%x  s0=%x", t0, t1, t2, s0);
+        $display("s1=%x  a0=%x  a1=%x  a2=%x", s1, a0, a1, a2);
+        $display("a3=%x  a4=%x  a5=%x  a6=%x", a3, a4, a5, a6);
+        $display("a7=%x  s2=%x  s3=%x  s4=%x", a7, s2, s3, s4);
+        $display("s5=%x  s6=%x  s7=%x  s8=%x", s5, s6, s7, s8);
+        $display("s9=%x s10=%x s11=%x  t3=%x", s9, s10, s11, t3);
+        $display("t4=%x  t5=%x  t6=%x", t4, t5, t6);
+    endfunction
+
+    reg [31:0] regs [0:30];
+
+    assign rs1_o = rs1_i == 0 ? 0 : regs[rs1_i - 1];
+    assign rs2_o = rs2_i == 0 ? 0 : regs[rs2_i - 1];
+
+    integer i;
+
+    always @(posedge clk_i) begin
+        if (rst_i) begin
+            for (i = 0; i < 31; ++i)
+                regs[i] <= 0;
+        end else begin
+            if (rd_write_i && rd_i > 0) begin
+                regs[rd_i - 1] <= write_value_i;
+            end
+        end
+    end
+endmodule
diff --git a/src/decoder/rvx0_decoder.sv b/src/decoder/rvx0_decoder.sv
new file mode 100644
index 0000000..5301e41
--- /dev/null
+++ b/src/decoder/rvx0_decoder.sv
@@ -0,0 +1,68 @@
+`include "rvx0_defs.svh"
+
+// Top-level instruction decoder module
+module rvx0_decoder (
+    input wire [31:0]   instruction_i,
+
+    output logic        write_pc_o,
+    output logic        write_mem_o,
+    output logic        conditional_o,
+
+    output logic        instruction_fault_o,
+    output wire [31:0]  imm_o,
+    output wire         v1src_o,
+    output wire [1:0]   v2src_o,
+    output wire [1:0]   vdsrc_o,
+    output wire [3:0]   aluop_o,
+    output wire [2:0]   funct3_o,
+    output wire [6:0]   funct7_o,
+    output wire [4:0]   rs1_o,
+    output wire [4:0]   rs2_o,
+    output wire [4:0]   rd_o
+);
+    wire [6:0] opcode;
+
+    wire signed [11:0] imm_i_type;
+    wire signed [11:0] imm_s_type;
+    wire signed [12:0] imm_b_type;
+    wire [19:0] imm_u_type;
+    wire signed [20:0] imm_j_type;
+
+    assign opcode = instruction_i[6:0];
+    assign funct3_o = instruction_i[14:12];
+    assign funct7_o = instruction_i[31:25];
+
+    assign imm_i_type = instruction_i[31:20];
+    assign imm_s_type = { instruction_i[31:25], instruction_i[11:7] };
+    assign imm_b_type = { instruction_i[31], instruction_i[7], instruction_i[30:25], instruction_i[11:8], 1'b0 };
+    assign imm_u_type = instruction_i[31:12];
+    assign imm_j_type = { instruction_i[31], instruction_i[19:12], instruction_i[20], instruction_i[30:21], 1'b0 };
+
+    assign rs1_o = instruction_i[19:15];
+    assign rs2_o = instruction_i[24:20];
+    assign rd_o = instruction_i[11:7];
+
+    rvx0_decoder_i decoder_i (
+        .instruction_i          (instruction_i),
+
+        .opcode                 (opcode),
+        .funct3                 (funct3_o),
+
+        .imm_i_type             (imm_i_type),
+        .imm_s_type             (imm_s_type),
+        .imm_b_type             (imm_b_type),
+        .imm_u_type             (imm_u_type),
+        .imm_j_type             (imm_j_type),
+
+        .write_pc_o             (write_pc_o),
+        .write_mem_o            (write_mem_o),
+        .conditional_o          (conditional_o),
+
+        .instruction_fault_o    (instruction_fault_o),
+        .imm_o                  (imm_o),
+        .v1src_o                (v1src_o),
+        .v2src_o                (v2src_o),
+        .vdsrc_o                (vdsrc_o),
+        .aluop_o                (aluop_o)
+    );
+endmodule
diff --git a/src/decoder/rvx0_decoder_i.sv b/src/decoder/rvx0_decoder_i.sv
new file mode 100644
index 0000000..565dc22
--- /dev/null
+++ b/src/decoder/rvx0_decoder_i.sv
@@ -0,0 +1,116 @@
+// Base rv32i instruction set decoder
+module rvx0_decoder_i (
+    input wire [31:0]           instruction_i,
+
+    input wire [6:0]            opcode,
+    input wire [2:0]            funct3,
+
+    input wire signed [11:0]    imm_i_type,
+    input wire signed [11:0]    imm_s_type,
+    input wire signed [12:0]    imm_b_type,
+    input wire [19:0]           imm_u_type,
+    input wire signed [20:0]    imm_j_type,
+
+    output logic                write_pc_o,
+    output logic                write_mem_o,
+    output logic                conditional_o,
+
+    output logic                instruction_fault_o,
+    output wire [31:0]          imm_o,
+    output wire                 v1src_o,
+    output wire [1:0]           v2src_o,
+    output wire [1:0]           vdsrc_o,
+    output wire [3:0]           aluop_o
+);
+    always_comb begin
+        write_pc_o = 0;
+        write_mem_o = 0;
+        conditional_o = 0;
+        instruction_fault_o = 0;
+        aluop_o = 0;
+
+        case (opcode)
+        7'b0110111: begin // lui
+            v1src_o = V1SRC_ZERO;
+            v2src_o = V2SRC_ZERO;
+            vdsrc_o = RDSRC_ALU;
+            imm_o = { imm_u_type, 12'b0 };
+        end
+        7'b0010111: begin // auipc
+            v1src_o = V1SRC_ZERO;
+            v2src_o = V2SRC_PC;
+            vdsrc_o = RDSRC_ALU;
+            imm_o = { imm_u_type, 12'b0 };
+        end
+        7'b1101111: begin // jal
+            v1src_o = V1SRC_ZERO;
+            v2src_o = V2SRC_PC;
+            vdsrc_o = RDSRC_PC;
+            write_pc_o = 1;
+            imm_o = 32'(signed'(imm_j_type));
+        end
+        7'b1100111: begin // jalr
+            v1src_o = V1SRC_RS1;
+            v2src_o = V2SRC_ZERO;
+            vdsrc_o = RDSRC_PC;
+            write_pc_o = 1;
+            imm_o = 32'(signed'(imm_i_type));
+        end
+        7'b1100011: begin // b.???
+            v1src_o = V1SRC_ZERO;
+            v2src_o = V2SRC_PC;
+            vdsrc_o = RDSRC_NONE;
+            write_pc_o = 1;
+            conditional_o = 1;
+            imm_o = 32'(signed'(imm_b_type));
+        end
+        7'b0000011: begin // load
+            v1src_o = V1SRC_RS1;
+            v2src_o = V2SRC_ZERO;
+            vdsrc_o = RDSRC_MEM;
+            imm_o = 32'(signed'(imm_i_type));
+        end
+        7'b0100011: begin // store
+            v1src_o = V1SRC_RS1;
+            v2src_o = V2SRC_ZERO;
+            vdsrc_o = RDSRC_NONE;
+            write_mem_o = 1;
+            imm_o = 32'(signed'(imm_s_type));
+        end
+        7'b0010011: begin // alu imm
+            v1src_o = V1SRC_RS1;
+            v2src_o = V2SRC_ZERO;
+            vdsrc_o = RDSRC_ALU;
+            case (funct3)
+            3'b001: begin
+                aluop_o = ALUOP_SLL;
+                imm_o = { 27'b0, instruction_i[24:20] };
+            end
+            3'b101: begin
+                aluop_o = { instruction_i[30], funct3 };
+                imm_o = { 27'b0, instruction_i[24:20] };
+            end
+            default: begin
+                aluop_o = { 1'b0, funct3 };
+                imm_o = 32'(signed'(imm_i_type));
+            end
+            endcase
+        end
+        7'b0110011: begin
+            v1src_o = V1SRC_RS1;
+            v2src_o = V2SRC_RS2;
+            vdsrc_o = RDSRC_ALU;
+            aluop_o = { instruction_i[30], funct3 };
+            imm_o = 0;
+        end
+        default: begin
+            v1src_o = V1SRC_ZERO;
+            v2src_o = V2SRC_ZERO;
+            vdsrc_o = RDSRC_NONE;
+            instruction_fault_o = 1;
+            imm_o = 0;
+        end
+        endcase
+
+    end
+endmodule
diff --git a/src/decoder/rvx0_decoder_tb.sv b/src/decoder/rvx0_decoder_tb.sv
new file mode 100644
index 0000000..c8ad29f
--- /dev/null
+++ b/src/decoder/rvx0_decoder_tb.sv
@@ -0,0 +1,122 @@
+/* verilator lint_off PINMISSING */
+
+`include "rvx0_defs.svh"
+
+module rvx0_decoder_tb ();
+    reg [31:0] instruction;
+
+    rvx0_decoder dut (
+        .instruction_i  (instruction)
+    );
+
+    initial begin
+        // lui sp, 0x12345
+        instruction = 'h12345137;
+        #1
+        assert(dut.imm_o == 'h12345000);
+        assert(dut.write_pc_o == 0);
+        assert(dut.v1src_o == V1SRC_ZERO);
+        assert(dut.v2src_o == V2SRC_ZERO);
+        assert(dut.vdsrc_o == RDSRC_ALU);
+        assert(dut.rd_o == 2);
+        assert(~dut.instruction_fault_o);
+
+        // auipc ra, 0xFEEF1
+        #1
+        instruction = 'hFEEF1097;
+        #1
+        assert(dut.imm_o == 'hFEEF1000);
+        assert(dut.write_pc_o == 0);
+        assert(dut.v1src_o == V1SRC_ZERO);
+        assert(dut.v2src_o == V2SRC_PC);
+        assert(dut.vdsrc_o == RDSRC_ALU);
+        assert(dut.rd_o == 1);
+        assert(~dut.instruction_fault_o);
+
+        // j . -> jal zero, 0
+        #1
+        instruction = 'h0000006f;
+        #1
+        assert(dut.imm_o == 0);
+        assert(dut.write_pc_o == 1);
+        assert(dut.v1src_o == V1SRC_ZERO);
+        assert(dut.v2src_o == V2SRC_PC);
+        assert(dut.vdsrc_o == RDSRC_PC);
+        assert(dut.rd_o == 0);
+        assert(~dut.instruction_fault_o);
+
+        // jalr x2, x3, 0x123
+        #1
+        instruction = 'hEDD18167;
+        #1
+        assert(dut.imm_o == -'h123);
+        assert(dut.write_pc_o == 1);
+        assert(dut.v1src_o == V1SRC_RS1);
+        assert(dut.v2src_o == V2SRC_ZERO);
+        assert(dut.vdsrc_o == RDSRC_PC);
+        assert(dut.rd_o == 2);
+        assert(dut.rs1_o == 3);
+        assert(~dut.instruction_fault_o);
+
+        // bne sp, gp, 0x24
+        #1
+        instruction = 'h02311263;
+        #1
+        assert(dut.imm_o == 'h24);
+        assert(dut.write_pc_o == 1);
+        assert(dut.conditional_o == 1);
+        assert(dut.v1src_o == V1SRC_ZERO);
+        assert(dut.v2src_o == V2SRC_PC);
+        assert(dut.vdsrc_o == RDSRC_NONE);
+        assert(dut.rs1_o == 2);
+        assert(dut.rs2_o == 3);
+        assert(dut.funct3_o == 'b001);
+        assert(~dut.instruction_fault_o);
+
+        // lw t0, 0x10(t1)
+        #1
+        instruction = 'h01032283;
+        #1
+        assert(dut.imm_o == 'h10);
+        assert(dut.write_pc_o == 0);
+        assert(dut.write_mem_o == 0);
+        assert(dut.v1src_o == V1SRC_RS1);
+        assert(dut.v2src_o == V2SRC_ZERO);
+        assert(dut.vdsrc_o == RDSRC_MEM);
+        assert(dut.rs1_o == 6);
+        assert(dut.rd_o == 5);
+        assert(dut.funct3_o == 'b010);
+        assert(~dut.instruction_fault_o);
+
+        // sh t0, -0x10(t1)
+        #1
+        instruction = 'hFE531823;
+        #1
+        assert(dut.imm_o == -'h10);
+        assert(dut.write_pc_o == 0);
+        assert(dut.write_mem_o == 1);
+        assert(dut.v1src_o == V1SRC_RS1);
+        assert(dut.v2src_o == V2SRC_ZERO);
+        assert(dut.vdsrc_o == RDSRC_NONE);
+        assert(dut.rs1_o == 6);
+        assert(dut.rs2_o == 5);
+        assert(dut.funct3_o == 'b001);
+        assert(~dut.instruction_fault_o);
+
+        // xori t0, t2, 0xC
+        #1
+        instruction = 'h00C3C293;
+        #1
+        assert(dut.imm_o == 'hC);
+        assert(dut.write_pc_o == 0);
+        assert(dut.write_mem_o == 0);
+        assert(dut.v1src_o == V1SRC_RS1);
+        assert(dut.v2src_o == V2SRC_ZERO);
+        assert(dut.vdsrc_o == RDSRC_ALU);
+        assert(dut.rd_o == 5);
+        assert(dut.rs1_o == 7);
+        assert(dut.funct3_o == 'b100);
+        assert(dut.aluop_o == 'b0100);
+        assert(~dut.instruction_fault_o);
+    end
+endmodule
diff --git a/src/rvx0_apb.sv b/src/rvx0_apb.sv
new file mode 100644
index 0000000..2200289
--- /dev/null
+++ b/src/rvx0_apb.sv
@@ -0,0 +1,25 @@
+/* verilator lint_off UNOPTFLAT */
+
+interface rvx0_apb ();
+    logic pclk;
+    logic prstn;
+    logic [31:0] paddr;
+    logic pwrite;
+    logic penable;
+    logic [31:0] pwdata;
+    logic psel;
+
+    logic pready;
+    logic [31:0] prdata;
+    logic pslverr;
+
+    modport master (
+        input pready, prdata, pslverr,
+        output pclk, prstn, paddr, penable, pwrite, pwdata
+    );
+
+    modport slave (
+        input pclk, prstn, paddr, pwrite, penable, pwdata, psel,
+        output pready, prdata, pslverr
+    );
+endinterface
diff --git a/src/rvx0_apb_debug.sv b/src/rvx0_apb_debug.sv
new file mode 100644
index 0000000..75f6cf8
--- /dev/null
+++ b/src/rvx0_apb_debug.sv
@@ -0,0 +1,20 @@
+module rvx0_apb_debug (
+    rvx0_apb.slave  apb_slave
+);
+    integer fd;
+
+    initial begin
+        fd = $fopen("debug.log", "w");
+    end
+
+    always @(posedge apb_slave.pclk) begin
+        if (apb_slave.prstn && apb_slave.penable) begin
+            if (apb_slave.pwrite) begin
+                $fwrite(fd, "%c", apb_slave.pwdata[7:0]);
+                $fflush(fd);
+            end
+
+            apb_slave.pready <= 1;
+        end
+    end
+endmodule
diff --git a/src/rvx0_busmux.sv b/src/rvx0_busmux.sv
new file mode 100644
index 0000000..f230e81
--- /dev/null
+++ b/src/rvx0_busmux.sv
@@ -0,0 +1,98 @@
+module rvx0_busmux (
+    // Uplink to core
+    rvx0_apb.slave apb_slave,
+
+    // Downlinks to peripherals/memory
+    rvx0_apb.master apb0_master,
+    rvx0_apb.master apb1_master,
+    rvx0_apb.master apb2_master,
+    rvx0_apb.master apb3_master
+);
+    // ROM
+    const logic [31:0] APB0_BASE = 'h00001000;
+    const logic [31:0] APB0_SIZE = 'h00020000;
+
+    // RAM
+    const logic [31:0] APB1_BASE = 'h20000000;
+    const logic [31:0] APB1_SIZE = 'h00001000;
+
+    // Debug
+    const logic [31:0] APB2_BASE = 'h10000000;
+    const logic [31:0] APB2_SIZE = 'h00001000;
+
+    // Forward pclk/prstn
+    assign apb0_master.pclk = apb_slave.pclk;
+    assign apb1_master.pclk = apb_slave.pclk;
+    assign apb2_master.pclk = apb_slave.pclk;
+    assign apb3_master.pclk = apb_slave.pclk;
+
+    assign apb0_master.prstn = apb_slave.prstn;
+    assign apb1_master.prstn = apb_slave.prstn;
+    assign apb2_master.prstn = apb_slave.prstn;
+    assign apb3_master.prstn = apb_slave.prstn;
+
+    always_comb begin
+        apb0_master.penable = 0;
+        apb1_master.penable = 0;
+        apb2_master.penable = 0;
+        apb3_master.penable = 0;
+
+        apb0_master.pwrite = 0;
+        apb1_master.pwrite = 0;
+        apb2_master.pwrite = 0;
+        apb3_master.pwrite = 0;
+
+        apb0_master.pwdata = 0;
+        apb1_master.pwdata = 0;
+        apb2_master.pwdata = 0;
+        apb3_master.pwdata = 0;
+
+        apb0_master.paddr = 0;
+        apb1_master.paddr = 0;
+        apb2_master.paddr = 0;
+        apb3_master.paddr = 0;
+
+        apb_slave.pready = 0;
+        apb_slave.pslverr = 0;
+        apb_slave.prdata = 0;
+
+        if (apb_slave.prstn && apb_slave.penable) begin
+            if (apb_slave.paddr >= APB0_BASE && apb_slave.paddr < APB0_BASE + APB0_SIZE) begin
+                // Connect to apb0
+                apb0_master.paddr = apb_slave.paddr - APB0_BASE;
+                apb0_master.pwdata = apb_slave.pwdata;
+                apb0_master.pwrite = apb_slave.pwrite;
+                apb0_master.penable = apb_slave.penable;
+
+                apb_slave.pready = apb0_master.pready && apb_slave.penable;
+                apb_slave.pslverr = apb0_master.pslverr;
+                apb_slave.prdata = apb0_master.prdata;
+            end else if (apb_slave.paddr >= APB1_BASE && apb_slave.paddr < APB1_BASE + APB1_SIZE) begin
+                // Connect to apb1
+                apb1_master.paddr = apb_slave.paddr - APB1_BASE;
+                apb1_master.pwdata = apb_slave.pwdata;
+                apb1_master.pwrite = apb_slave.pwrite;
+                apb1_master.penable = apb_slave.penable;
+
+                apb_slave.pready = apb1_master.pready && apb_slave.penable;
+                apb_slave.pslverr = apb1_master.pslverr;
+                apb_slave.prdata = apb1_master.prdata;
+            end else if (apb_slave.paddr >= APB2_BASE && apb_slave.paddr < APB2_BASE + APB2_SIZE) begin
+                // Connect to apb2
+                apb2_master.paddr = apb_slave.paddr - APB2_BASE;
+                apb2_master.pwdata = apb_slave.pwdata;
+                apb2_master.pwrite = apb_slave.pwrite;
+                apb2_master.penable = apb_slave.penable;
+
+                apb_slave.pready = apb2_master.pready && apb_slave.penable;
+                apb_slave.pslverr = apb2_master.pslverr;
+                apb_slave.prdata = apb2_master.prdata;
+            end else begin
+                // Raise bus error
+                apb_slave.pslverr = 1;
+            end
+        end else begin
+            apb_slave.pslverr = 0;
+        end
+    end
+endmodule
diff --git a/src/rvx0_defs.svh b/src/rvx0_defs.svh
new file mode 100644
index 0000000..0e1f65c
--- /dev/null
+++ b/src/rvx0_defs.svh
@@ -0,0 +1,61 @@
+`ifndef __RVX0_DEFS_SVH
+`define __RVX0_DEFS_SVH
+
+`define RVX0_DEBUGGING  1
+
+const logic [1:0]   RDSRC_ALU = 0;
+const logic [1:0]   RDSRC_MEM = 1;
+const logic [1:0]   RDSRC_PC = 2;
+const logic [1:0]   RDSRC_NONE = 3;
+
+const logic         V1SRC_ZERO = 0;
+const logic         V1SRC_RS1 = 1;
+
+const logic [1:0]   V2SRC_ZERO = 0;
+const logic [1:0]   V2SRC_RS2 = 1;
+const logic [1:0]   V2SRC_PC = 2;
+
+const logic [3:0]   ALUOP_ADD   = 4'b0000;
+const logic [3:0]   ALUOP_SLL   = 4'b0001;
+const logic [3:0]   ALUOP_SLT   = 4'b0010;
+const logic [3:0]   ALUOP_SLTU  = 4'b0011;
+const logic [3:0]   ALUOP_XOR   = 4'b0100;
+const logic [3:0]   ALUOP_SRL   = 4'b0101;
+const logic [3:0]   ALUOP_OR    = 4'b0110;
+const logic [3:0]   ALUOP_AND   = 4'b0111;
+const logic [3:0]   ALUOP_SUB   = 4'b1000;
+const logic [3:0]   ALUOP_SRA   = 4'b1101;
+
+const logic [2:0]   COND_EQ     = 3'b000;
+const logic [2:0]   COND_NE     = 3'b001;
+const logic [2:0]   COND_LT     = 3'b100;
+const logic [2:0]   COND_GE     = 3'b101;
+const logic [2:0]   COND_LTU    = 3'b110;
+const logic [2:0]   COND_GEU    = 3'b111;
+
+const logic [1:0]   CSTATE_FETCH = 0;
+const logic [1:0]   CSTATE_READ = 1;
+const logic [1:0]   CSTATE_EXEC = 2;
+const logic [1:0]   CSTATE_WRITE = 3;
+
+const logic [31:0]  MISA_MXLEN_32 = 1 << 30;
+
+const logic [31:0]  MCAUSE_INSTRUCTION_ADDRESS_MISALIGN = 0;
+const logic [31:0]  MCAUSE_INSTRUCTION_ACCESS_FAULT = 1;
+const logic [31:0]  MCAUSE_ILLEGAL_INSTRUCTION = 2;
+const logic [31:0]  MCAUSE_BREAKPOINT = 3;
+const logic [31:0]  MCAUSE_LOAD_ADDRESS_MISALIGNED = 4;
+const logic [31:0]  MCAUSE_LOAD_ACCESS_FAULT = 5;
+const logic [31:0]  MCAUSE_STORE_ADDRESS_MISALIGNED = 6;
+const logic [31:0]  MCAUSE_STORE_ACCESS_FAULT = 7;
+const logic [31:0]  MCAUSE_ECALL_UMODE = 8;
+const logic [31:0]  MCAUSE_ECALL_SMODE = 9;
+const logic [31:0]  MCAUSE_ECALL_MMODE = 11;
+const logic [31:0]  MCAUSE_INSTRUCTION_PAGE_FAULT = 12;
+const logic [31:0]  MCAUSE_LOAD_PAGE_FAULT = 13;
+const logic [31:0]  MCAUSE_STORE_PAGE_FAULT = 15;
+
+const logic [31:0]  MCAUSE_INTR_EXT_MMODE = 11;
+const logic [31:0]  MCAUSE_INTERRUPT = 1 << 31;
+
+`endif // __RVX0_DEFS_SVH
diff --git a/src/rvx0_simple_ram.sv b/src/rvx0_simple_ram.sv
new file mode 100644
index 0000000..e6f5b29
--- /dev/null
+++ b/src/rvx0_simple_ram.sv
@@ -0,0 +1,30 @@
+module rvx0_simple_ram (
+    rvx0_apb.slave  apb_slave
+);
+    reg [31:0]  words [0:1023];
+
+    integer i;
+
+    always @(posedge apb_slave.pclk) begin
+        if (apb_slave.prstn) begin
+            if (apb_slave.penable) begin
+                if (apb_slave.pwrite) begin
+                    words[apb_slave.paddr[11:2]] <= apb_slave.pwdata;
+                    $display("RAM write [%x] <= %x", apb_slave.paddr, apb_slave.pwdata);
+                end else begin
+                    apb_slave.prdata <= words[apb_slave.paddr[11:2]];
+                    $display("RAM read %x <= [%x]", words[apb_slave.paddr[11:2]], apb_slave.paddr);
+                end
+
+                apb_slave.pready <= 1;
+            end else begin
+                apb_slave.pready <= 0;
+            end
+        end else begin
+            // for (i = 0; i < 1024; ++i)
+            //     words[i] <= 0;
+
+            words[0] <= 'h11223344;
+        end
+    end
+endmodule
diff --git a/src/rvx0_simple_rom.sv b/src/rvx0_simple_rom.sv
new file mode 100644
index 0000000..eb19a2e
--- /dev/null
+++ b/src/rvx0_simple_rom.sv
@@ -0,0 +1,15 @@
+module rvx0_simple_rom (
+    rvx0_apb.slave  apb_slave
+);
+    // 1 page
+    reg [31:0]  words [0:32768 - 1];
+
+    always_comb begin
+        apb_slave.pready = apb_slave.penable;
+        apb_slave.prdata = words[apb_slave.paddr[16:2]];
+    end
+
+    initial begin
+        $readmemh("obj_dir/apb0_memory.hex", words);
+    end
+endmodule
diff --git a/src/rvx0_soc_top.sv b/src/rvx0_soc_top.sv
new file mode 100644
index 0000000..e5c14b3
--- /dev/null
+++ b/src/rvx0_soc_top.sv
@@ -0,0 +1,67 @@
+`include "rvx0_defs.svh"
+
+/* verilator lint_off PINMISSING */
+
+module rvx0_soc_top ();
+    logic clk;
+    logic rst;
+    logic intr_ext;
+
+    rvx0_apb apb ();
+
+    rvx0_apb apb0 ();
+    rvx0_apb apb1 ();
+    rvx0_apb apb2 ();
+    rvx0_apb apb3 ();
+
+    rvx0_core #(
+        .RESET_VECTOR   ('h00001000)
+    ) core (
+        .clk_i          (clk),
+        .rst_i          (rst),
+        .intr_ext_i     (intr_ext),
+        .apb_master     (apb)
+    );
+
+    rvx0_simple_rom rom (
+        .apb_slave      (apb0)
+    );
+
+    rvx0_simple_ram ram (
+        .apb_slave      (apb1)
+    );
+
+    rvx0_apb_debug debug (
+        .apb_slave      (apb2)
+    );
+
+    rvx0_busmux busmux (
+        .apb_slave      (apb),
+
+        .apb0_master    (apb0),
+        .apb1_master    (apb1),
+        .apb2_master    (apb2),
+        .apb3_master    (apb3)
+    );
+
+    always #10 clk <= ~clk;
+
+    assign apb.pclk = clk;
+    assign apb.prstn = ~rst;
+
+    initial begin
+        #0
+        intr_ext = 0;
+        rst = 1;
+
+        #20
+        rst = 0;
+
+        // #50000
+
+        // // Dump state
+        // $display("Finish with pc=%x", core.pc_value);
+        // core.regfile.dump_state;
+        // $finish;
+    end
+endmodule
diff --git a/tool/makebin.py b/tool/makebin.py
new file mode 100755
index 0000000..3c4b9b3
--- /dev/null
+++ b/tool/makebin.py
@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+
+import sys
+import struct
+
+if __name__ == "__main__":
+    if len(sys.argv) != 3:
+        print(f"Usage: {sys.argv[0]} SOURCE.BIN OUTPUT.HEX", file=sys.stderr)
+        sys.exit(2)
+
+    data = None
+    with open(sys.argv[1], "rb") as fp:
+        data = fp.read()
+
+    with open(sys.argv[2], "w") as fp:
+        for i in range(0, len(data), 4):
+            word = data[i:i + 4]
+            word = struct.unpack("<I", word)[0]
+            fp.write(f"{word:x}\n")
+
+