quadrotor/uart.c

#include "uart.h"
#include "types.h"
#include "interrupt.h"
#include "event.h"

#define UARTBASE 0xE000C000

#define RBR 0x00
#define THR 0x00
#define DLL 0x00
#define DLM 0x04
#define IER 0x04
#define IIR 0x08
#define FCR 0x08

#define LCR 0x0c
#define LSR 0x14
#define SCR 0x1c
#define ACR 0x20
#define FDR 0x28
#define TER 0x30

#define UREG(x) (((volatile unsigned char *)UARTBASE)[x])

#define U0THRE ((UREG(LSR) & (1<<5))) /* UART0 transmitter holding register is empty */
#define U0DR ((UREG(LSR) & (1<<0))) /* UART0 data ready */

#define UART_TXBUFSIZE 128
#define UART_RXBUFSIZE 128

char uart_txbuf[UART_TXBUFSIZE];
char uart_rxbuf[UART_RXBUFSIZE];
volatile int uart_txread;
volatile int uart_txwrite;
volatile int uart_rxread;
volatile int uart_rxwrite;
volatile bool tx_running;

void __attribute__((interrupt("IRQ"))) uart_interrupt_handler(void);

void init_uart(void)
{
	UREG(FDR) = 0x10; /* DivAddVal = 0, MulVal = 1 */

	UREG(LCR) = 0x80;
	UREG(DLM) = 0x00;
	UREG(DLL) = 0x08; /* 14745600 / (16*115200) */
	UREG(LCR) = 0x13;
	UREG(FCR) = 0x07;

	uart_txread = 0;
	uart_txwrite = 0;
	uart_rxread = 0;
	uart_rxwrite = 0;
	tx_running = FALSE;
	interrupt_register(UART0, uart_interrupt_handler);

	UREG(IER) = 0x03; /* RBR and THRE interrupt enable */
}

void putch(char c) {
	/* Wait for space in the buffer */
	while (uart_txread == ((uart_txwrite+1) % UART_TXBUFSIZE));

	if (uart_txread == uart_txwrite) {
		if (U0THRE) {
			tx_running = TRUE;
			UREG(THR) = c;
			return;
		}
	}

	uart_txbuf[uart_txwrite] = c;
	uart_txwrite = (uart_txwrite + 1) % UART_TXBUFSIZE;

	if (!tx_running) {
		if (uart_txread != uart_txwrite) {
			tx_running = TRUE;
			uart_txread = (uart_txread + 1) % UART_TXBUFSIZE;
			UREG(THR) = c;
		}
	}
}

void __attribute__((interrupt("IRQ"))) uart_interrupt_handler(void)
{
	bool active = FALSE;
	int source;
	int i;
	/* uart_txread and uart_txwrite are volatile. We don't need
	 * to treat them as such in this handler, so let the compiler
	 * have an easier time.
	 */
	int local_txwrite;
	int local_txread;
	int local_rxwrite;
	int local_rxread;

	source = UREG(IIR);

	switch (source & 0x0e) {
	case 0x4: /* Receive Data Available */
	case 0xc: /* Character Time-out Indicator */
		local_rxwrite = uart_rxwrite;
		local_rxread = uart_rxread;
		while (U0DR) {
			unsigned char c = UREG(RBR);
			if (local_rxread !=
			    ((local_rxwrite+1) % UART_RXBUFSIZE)) {
				uart_rxbuf[local_rxwrite] = c;
				local_rxwrite = (local_rxwrite + 1) %
				    UART_RXBUFSIZE;
			}
		}
		uart_rxwrite = local_rxwrite;
		event_set(EVENT_UART_INPUT);
		break;

	case 0x2: /* THRE interrupt */
		local_txwrite = uart_txwrite;
		local_txread = uart_txread;
		for (i = 0; (i < 16) && (local_txwrite != local_txread); i++) {
			UREG(THR) = uart_txbuf[local_txread];
			local_txread = (local_txread + 1) % UART_TXBUFSIZE;
			active = TRUE;
		}
		uart_txread = local_txread;
		if (!active)
			tx_running = FALSE;
		break;

	case 0x6: /* Receive Line Status */
	default: /* Anything else */
		break;
	}

	interrupt_clear();
}

void putstr(char *s) {
	while (*s) putch(*s++);
}

void putint(unsigned int n) {
	char s[11];
	int i;

	i = 10;
	s[i] = '\0';

	do {
		s[--i] = n % 10 + '0';
	} while ((n /= 10) > 0);

	putstr(s+i);
}

void putint_s(int n) {
	char s[12];
	int i;
	int neg;

	/* OK, technically, this might not work properly for the most
	 * negative possible number. Oh well.
	 */
	neg = (n < 0);
	if (neg)
		n = -n;

	i = 11;
	s[i] = '\0';

	do {
		s[--i] = n % 10 + '0';
	} while ((n /= 10) > 0);

	if (neg)
		s[--i] = '-';

	putstr(s+i);
}

void puthex(unsigned int n) {
	char s[9];
	int i;

	i = 8;
	s[i] = '\0';

	do {
		int x = n % 16;
		if (x > 9)
			x += 'A' - '0' - 10;
		s[--i] = x + '0';
	} while ((n /= 16) > 0);

	putstr(s+i);
}

bool getch(char *c) {
	if (uart_rxread == uart_rxwrite)
		return FALSE;

	*c = uart_rxbuf[uart_rxread];
	uart_rxread = (uart_rxread + 1) % UART_RXBUFSIZE;
	return TRUE;
}