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extern "C" void kernel_main();
#define UART_ADDR 0x10000000UL
#define THR_OFFSET 0x0
#define LSR_OFFSET 0x5
#define FCR_OFFSET 0x2
#define LCR_OFFSET 0x3
#define DLL_OFFSET 0x0
#define DLH_OFFSET 0x1
static void
write_byte(unsigned long addr, char byte)
{
*((volatile char *)addr) = byte;
}
static int
is_tx_empty()
{
return *((volatile char *)(UART_ADDR + LSR_OFFSET)) & (1 << 5);
}
void uart_init()
{
write_byte(UART_ADDR + LCR_OFFSET, 0x80);
write_byte(UART_ADDR + DLL_OFFSET, 0x01);
write_byte(UART_ADDR + DLH_OFFSET, 0x00);
write_byte(UART_ADDR + LCR_OFFSET, 0x03);
write_byte(UART_ADDR + FCR_OFFSET, 0x07);
}
void put_char(char c)
{
if (c == '\n')
{
put_char('\r');
}
while (!is_tx_empty())
{
}
write_byte(UART_ADDR + THR_OFFSET, c);
}
void print_str(const char *s)
{
while (*s != '\0')
{
put_char(*s++);
}
}
void kernel_main()
{
uart_init();
print_str("Modern DOS 1.0\n");
print_str("Hello OS! Running on RISC-V 64.\n");
print_str("Hello Ziyi Yang! Love from RUC");
while (1)
{
}
}
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