litex/software/libbase/uart.c

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/*
* Milkymist SoC (Software)
* Copyright (C) 2007, 2008, 2009, 2010, 2012 Sebastien Bourdeauducq
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, version 3 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <uart.h>
#include <irq.h>
#include <hw/uart.h>
#include <hw/interrupts.h>
/*
* Buffer sizes must be a power of 2 so that modulos can be computed
* with logical AND.
* RX functions are written in such a way that they do not require locking.
* TX functions already implement locking.
*/
#define UART_RINGBUFFER_SIZE_RX 128
#define UART_RINGBUFFER_MASK_RX (UART_RINGBUFFER_SIZE_RX-1)
static char rx_buf[UART_RINGBUFFER_SIZE_RX];
static volatile unsigned int rx_produce;
static volatile unsigned int rx_consume;
#define UART_RINGBUFFER_SIZE_TX 128
#define UART_RINGBUFFER_MASK_TX (UART_RINGBUFFER_SIZE_TX-1)
static char tx_buf[UART_RINGBUFFER_SIZE_TX];
static unsigned int tx_produce;
static unsigned int tx_consume;
static volatile int tx_cts;
void uart_isr(void)
{
unsigned int stat = CSR_UART_STAT;
if(stat & UART_STAT_RX_EVT) {
rx_buf[rx_produce] = CSR_UART_RXTX;
rx_produce = (rx_produce + 1) & UART_RINGBUFFER_MASK_RX;
}
if(stat & UART_STAT_TX_EVT) {
if(tx_produce != tx_consume) {
CSR_UART_RXTX = tx_buf[tx_consume];
tx_consume = (tx_consume + 1) & UART_RINGBUFFER_MASK_TX;
} else
tx_cts = 1;
}
CSR_UART_STAT = stat;
irq_ack(IRQ_UART);
}
/* Do not use in interrupt handlers! */
char uart_read(void)
{
char c;
while(rx_consume == rx_produce);
c = rx_buf[rx_consume];
rx_consume = (rx_consume + 1) & UART_RINGBUFFER_MASK_RX;
return c;
}
int uart_read_nonblock(void)
{
return (rx_consume != rx_produce);
}
void uart_write(char c)
{
unsigned int oldmask;
oldmask = irq_getmask();
irq_setmask(0);
if(tx_cts) {
tx_cts = 0;
CSR_UART_RXTX = c;
} else {
tx_buf[tx_produce] = c;
tx_produce = (tx_produce + 1) & UART_RINGBUFFER_MASK_TX;
}
irq_setmask(oldmask);
}
void uart_init(void)
{
unsigned int mask;
rx_produce = 0;
rx_consume = 0;
tx_produce = 0;
tx_consume = 0;
tx_cts = 1;
irq_ack(IRQ_UART);
/* ack any events */
CSR_UART_STAT = CSR_UART_STAT;
/* enable interrupts */
CSR_UART_CTRL = UART_CTRL_TX_INT | UART_CTRL_RX_INT;
mask = irq_getmask();
mask |= IRQ_UART;
irq_setmask(mask);
}
void uart_sync(void)
{
while(!tx_cts);
}