sunxi-h6-example/kernel.c

#include <stdint.h>

#define UART0_BASE      0x05000000
#define R_WDOG_BASE     0x07020400

#define WDOG_CTRL_KEY       (0xA57 << 1)
#define WDOG_CTRL_RESTART   (1 << 0)
#define WDOG_CFG_SYS        (1 << 0)
#define WDOG_MODE_EN        (1 << 0)

struct watchdog {
    uint32_t irq_en;
    uint32_t irq_sta;
    uint32_t res[2];
    uint32_t ctrl;
    uint32_t cfg;
    uint32_t mode;
};

static volatile struct watchdog *const r_wdog = (struct watchdog *) R_WDOG_BASE;

static inline void delay(uint32_t t) {
    for (uint32_t i = 0; i < t; ++i) {
        asm volatile ("nop");
    }
}

static void uart_tx(uint8_t byte) {
    *((uint8_t *) UART0_BASE) = byte;
}

static _Noreturn void board_reset(void) {
    // NOTE: this seems to be the suggested method for
    //       h6 board reset according to u-boot
    r_wdog->cfg = WDOG_CFG_SYS;
    r_wdog->mode = WDOG_MODE_EN;
    r_wdog->ctrl = WDOG_CTRL_KEY | WDOG_CTRL_RESTART;
    while (1);
}

_Noreturn void kernel_main(uintptr_t dt_phys_addr) {
    for (const char *p = "It's alive\r\n"; *p; ++p) {
        uart_tx(*p);
        delay(1000);
    }

    board_reset();
}