b288 uart putc baremetal

// SPDX-License-Identifier: GPL-2.0 or later
// Made by Soupborsh, tested on PB618. I tried to do puts function but it outputs garbage

// compile and run this by:
// arm-none-eabi-gcc -I /usr/include/ -nostdlib -nostartfiles -static serial-putc.c -o serial-putc -O3
// arm-none-eabi-objcopy -O binary serial-putc serial-putc.bin
// sunxi-fel write 0x2000 /path/to/serial-putc.bin
// sunxi-fel exe 0x2000

#include <stdint.h>

#define UART0_BASE 0x01c28000
#define UART_VALUE_TX_MODE 0x00100000
#define UART_VALUE_RX_MODE 0x00000000
#define UART_VALUE_CHAR 0x000000ff

uint32_t inline readl(volatile uint32_t *address);
void inline writel(volatile uint32_t *address, uint32_t value);
void uart_putc(const char c);

void main(void) {
  uart_putc('B');
  uart_putc('2');
  uart_putc('8');
  uart_putc('8');
  uart_putc('\n');
  return;
}

void inline writel(volatile uint32_t *address, uint32_t value) {
  volatile uint32_t *ptr = address;
  *ptr = value;
  return;
}

uint32_t inline readl(volatile uint32_t *address) {
  volatile uint32_t *ptr = address;
  return *ptr;
}

void uart_putc(const char c) {
  while (((readl((volatile uint32_t *)UART0_BASE)) & UART_VALUE_TX_MODE) !=
         UART_VALUE_RX_MODE)
    ;
  writel((volatile uint32_t *)UART0_BASE,
         UART_VALUE_TX_MODE | (c & UART_VALUE_CHAR));
}