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// AVR serial port code.
//
// Copyright (C) 2016 Kevin O'Connor <kevin@koconnor.net>
//
// This file may be distributed under the terms of the GNU GPLv3 license.
#include <avr/interrupt.h> // USART0_RX_vect
#include <string.h> // memmove
#include "autoconf.h" // CONFIG_SERIAL_BAUD
#include "sched.h" // DECL_INIT
#include "irq.h" // irq_save
#include "misc.h" // console_get_input
#define SERIAL_BUFFER_SIZE 96
static char receive_buf[SERIAL_BUFFER_SIZE];
static uint8_t receive_pos;
static char transmit_buf[SERIAL_BUFFER_SIZE];
static uint8_t transmit_pos, transmit_max;
/****************************************************************
* Serial hardware
****************************************************************/
static void
serial_init(void)
{
if (CONFIG_SERIAL_BAUD_U2X) {
UCSR0A = 1<<U2X0;
UBRR0 = DIV_ROUND_CLOSEST(F_CPU, 8UL * CONFIG_SERIAL_BAUD) - 1UL;
} else {
UCSR0A = 0;
UBRR0 = DIV_ROUND_CLOSEST(F_CPU, 16UL * CONFIG_SERIAL_BAUD) - 1UL;
}
UCSR0C = (1<<UCSZ01) | (1<<UCSZ00);
UCSR0B = (1<<RXEN0) | (1<<TXEN0) | (1<<RXCIE0) | (1<<UDRIE0);
}
DECL_INIT(serial_init);
#ifdef USART_RX_vect
#define USART0_RX_vect USART_RX_vect
#define USART0_UDRE_vect USART_UDRE_vect
#endif
// Rx interrupt - data available to be read.
ISR(USART0_RX_vect)
{
uint8_t data = UDR0;
if (receive_pos >= sizeof(receive_buf))
// Serial overflow - ignore it as crc error will force retransmit
return;
receive_buf[receive_pos++] = data;
}
// Tx interrupt - data can be written to serial.
ISR(USART0_UDRE_vect)
{
if (transmit_pos >= transmit_max)
UCSR0B &= ~(1<<UDRIE0);
else
UDR0 = transmit_buf[transmit_pos++];
}
/****************************************************************
* Console access functions
****************************************************************/
// Return a buffer (and length) containing any incoming messages
char *
console_get_input(uint8_t *plen)
{
*plen = readb(&receive_pos);
return receive_buf;
}
// Remove from the receive buffer the given number of bytes
void
console_pop_input(uint8_t len)
{
uint8_t copied = 0;
for (;;) {
uint8_t rpos = readb(&receive_pos);
uint8_t needcopy = rpos - len;
if (needcopy) {
memmove(&receive_buf[copied], &receive_buf[copied + len]
, needcopy - copied);
copied = needcopy;
}
uint8_t flag = irq_save();
if (rpos != readb(&receive_pos)) {
// Raced with irq handler - retry
irq_restore(flag);
continue;
}
receive_pos = needcopy;
irq_restore(flag);
break;
}
}
// Return an output buffer that the caller may fill with transmit messages
char *
console_get_output(uint8_t len)
{
uint8_t tpos = readb(&transmit_pos), tmax = readb(&transmit_max);
if (tpos == tmax) {
tpos = tmax = 0;
writeb(&transmit_max, 0);
writeb(&transmit_pos, 0);
}
if (tmax + len <= sizeof(transmit_buf))
return &transmit_buf[tmax];
if (tmax - tpos + len > sizeof(transmit_buf))
return NULL;
// Disable TX irq and move buffer
writeb(&transmit_max, 0);
barrier();
tpos = readb(&transmit_pos);
tmax -= tpos;
memmove(&transmit_buf[0], &transmit_buf[tpos], tmax);
writeb(&transmit_pos, 0);
barrier();
writeb(&transmit_max, tmax);
UCSR0B |= 1<<UDRIE0;
return &transmit_buf[tmax];
}
// Accept the given number of bytes added to the transmit buffer
void
console_push_output(uint8_t len)
{
writeb(&transmit_max, readb(&transmit_max) + len);
// enable TX interrupt
UCSR0B |= 1<<UDRIE0;
}
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