firmware.c

#include <stdint.h>
#include <stdbool.h>
#include "printf.h"

// a pointer to this is a null pointer, but the compiler does not
// know that because "sram" is a linker symbol from sections.lds.
extern uint32_t sram;

#define reg_spi_cfg  (*(volatile uint32_t*)0x02000000)
#define reg_uart_div (*(volatile uint32_t*)0x02000004)
#define reg_uart_dat (*(volatile uint32_t*)0x02000008)

#define reg_gpio_do  (*(volatile uint32_t*)0x03000000)
#define reg_gpio_di  (*(volatile uint32_t*)0x03000000)
#define reg_gpio_oe  (*(volatile uint32_t*)0x03000004)
#define reg_gpio_alt (*(volatile uint32_t*)0x03000008)

extern uint32_t _sidata, _sdata, _edata, _sbss, _ebss,_heap_start;

struct uart_output {
    struct output out;
};

void uart_out(struct output *_out, char c){
    reg_uart_dat = ((uint32_t) c) & 0xff;
}

void uart_printf(char *fmtstr, ...){
    struct uart_output uart = {
        .out = {
            .out = uart_out
        }
    };
    va_list va;
    va_start(va, fmtstr);
    va_printf(&uart.out, fmtstr, va);
}

int do_rdcycle();
int do_rdinstret();

void main() {
    // zero out .bss section
    for (uint32_t *dest = &_sbss; dest < &_ebss;) {
        *dest++ = 0;
    }

    // blink the user LED
    uint32_t led_timer = 0;
    reg_uart_div = 139;
       
    //reg_spi_cfg = (reg_spi_cfg & ~0x007F0000) | 0x00400000;
    reg_gpio_oe = 0x00000001;
    reg_gpio_do = 0;
    reg_gpio_alt = (1 << 4) | (1 << 3);

    uint32_t num = 0;
    asm("fence");
    while (1) {
        if(led_timer & 0x10000) {
            uart_printf("Iteration %d (rdcycle = %d, rdinstret = %d)\n", num++, do_rdcycle(), do_rdinstret());
            reg_gpio_do ^= 1;
            led_timer = 0;
        }
        led_timer = led_timer + 1;
    } 
}