kernel.c

#include <stddef.h>
#include <stdint.h>

static inline void mmio_write(uint32_t reg,uint32_t data){
	*(volatile uint32_t*)reg = data;
}
static inline uint32_t mmio_read(uint32_t reg){
	return *(volatile uint32_t*) reg;
}
static inline void delay(int32_t count){
	asm volatile(
		"__delay_%=: subs %[count], %[count], #1; bne __delay_%=\n" : "=r" (count):[count]"0"(count) : "cc" );
}
//should move this to the uart file laters
//the GPIO is offered as a list of memory addresses all we need to do is add handles to the addressses to get to the functions they host
enum{
	GPIO_BASE = 0x3F200000,
	GPPUD = (GPIO_BASE + 0x94),
	GPPUDCLK0 = (GPIO_BASE + 0x98),
	
	UART0_BASE = 0x3F201000,
	
	UART0_DR = (UART0_BASE + 0x00),
	UART0_RSRECR = (UART0_BASE + 0x04),
	UART0_FR = (UART0_BASE + 0x18),
	UART0_ILPR = (UART0_BASE + 0x20),
	UART0_IBRD = (UART0_BASE + 0x24),
	UART0_FBRD = (UART0_BASE + 0x28),
	UART0_LCRH = (UART0_BASE + 0x2C),
	UART0_CR = (UART0_BASE + 0x30),
	UART0_IFLS = (UART0_BASE + 0x34),
	UART0_IMSC = (UART0_BASE + 0x38),
	UART0_RIS = (UART0_BASE + 0x3C),
	UART0_MIS = (UART0_BASE + 0x40),
	UART0_ICR = (UART0_BASE + 0x44),
	UART0_DMACR = (UART0_BASE + 0x48),
	UART0_ITCR = (UART0_BASE + 0x80),
	UART0_ITIP = (UART0_BASE + 0x84),
	UART0_ITOP = (UART0_BASE + 0x88),
	UART0_TDR = (UART0_BASE + 0x8C)
};

/*
void uart_init();
	- set up registers and turn off the functions we don't need
*/
void uart_init(){
	mmio_write(UART0_CR,0x000000);
	mmio_write(GPPUD,0x00000000);
	delay(150);
	
	mmio_write(GPPUDCLK0, (1 << 14) | (1 << 15));
	delay(150);
	mmio_write(GPPUDCLK0,0x00000000);
	mmio_write(UART0_ICR,0x7FF);
	mmio_write(UART0_IBRD,1);
	mmio_write(UART0_FBRD,40);

	mmio_write(UART0_IMSC, (1 << 1) | (1 << 4) | (1 << 5) | (1 << 6));
	mmio_write(UART0_LCRH, (1 << 4) |
								  (1 << 5) | 
								  (1 << 6) |
								  (1 << 7) |
								  (1 << 8) |
								  (1 << 9) | 
								  (1 << 10));
	mmio_write(UART0_CR, (1 << 0) | 
								(1 << 8) |
								(1 << 9));
}
void uart_putc(unsigned char c){

	while ( mmio_read(UART0_FR) & ( 1 << 5)) {}	
	mmio_write(UART0_DR, c);
}

unsigned char uart_getc(){
	while ( mmio_read(UART0_FR) & ( 1 << 4)) {}	
	return mmio_read(UART0_DR);
}
void uart_puts(const char* str){
	for (size_t i = 0; str[i] != '\0';i++){
		uart_putc((unsigned char) str[i]);
	}
}
void kernel_main(uint32_t r0, uint32_t r1, uint32_t atags){
	(void) r0;
	(void) r1;
	(void) atags;
	
	//we are probably going to do some cool stuff with the atags later 
	uart_init();
	uart_puts("Hi this is Keith's raspberry pi kernel :)\r\n");
	uart_puts("Anyting you'd like to say:");
	
	while(1){
		uart_putc(uart_getc());
	}

}