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Merge pull request #5617 from jthacker/avr__uart_double_speed

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cpu/atmega_common: Add support for double speed baud generator
This commit is contained in:
kYc0o 2016-08-24 00:41:04 +02:00 committed by GitHub
commit 932541678b
1 changed files with 58 additions and 2 deletions
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60
cpu/atmega_common/periph/uart.c
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@ -16,6 +16,15 @@
* @author Hauke Petersen <hauke.petersen@fu-berlin.de>
* @author Hinnerk van Bruinehsen <h.v.bruinehsen@fu-berlin.de>
*
*
* Support static BAUD rate calculation using UART_STDIO_BAUDRATE.
* Set UART_STDIO_BAUDRATE to the desired baud rate and pass it as a -D argument
* at compliation time (e.g. in the boards Makefile.include file).
* UART_BAUD_TOL can be set to guarantee a BAUD rate tolerance at compile time or
* to switch to double speed transmission (U2X) to achieve a lower tolerance.
* At runtime, this tolerance is not guaranteed to be met.
* However, an error message will be displayed at compile time.
*
* @}
*/
@ -25,6 +34,26 @@
#include "periph/uart.h"
/**
* @brief Maximum percentage error in calculated baud before switching to double speed transmission (U2X)
*
* Takes whole numbers from 0 to 100, inclusive, with a default of 2.
*/
#if defined(UART_BAUD_TOL)
// BAUD_TOL is defined here as it is used by the setbaud.h utility
#define BAUD_TOL UART_BAUD_TOL
#else
#define BAUD_TOL 2
#endif
#if defined(UART_STDIO_BAUDRATE)
// BAUD and F_CPU are required by setbaud.h to calculated BRR
#define BAUD UART_STDIO_BAUDRATE
#define F_CPU CLOCK_CORECLOCK
#include <util/setbaud.h>
#endif
/**
* @brief Configured device map
* @{
@ -54,6 +83,33 @@ static const mega_uart_t *dev[] = { NULL };
*/
static uart_isr_ctx_t isr_ctx[UART_NUMOF];
static void _update_brr(uart_t uart, uint16_t brr, bool double_speed)
{
dev[uart]->BRR = brr;
if (double_speed) {
dev[uart]->CSRA |= (1 << U2X0);
}
}
static void _set_brr(uart_t uart, uint32_t baudrate)
{
uint16_t brr;
#if defined(UART_STDIO_BAUDRATE)
// UBRR_VALUE and USE_2X are statically computed from <util/setbaud.h>
if (baudrate == UART_STDIO_BAUDRATE) {
_update_brr(uart, UBRR_VALUE, USE_2X);
return;
}
#endif
#if defined(UART_DOUBLE_SPEED)
brr = (CLOCK_CORECLOCK + 4UL * baudrate) / (8UL * baudrate) - 1UL;
_update_brr(uart, brr, true);
#else
brr = (CLOCK_CORECLOCK + 8UL * baudrate) / (16UL * baudrate) - 1UL;
_update_brr(uart, brr, false);
#endif
}
int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
{
/* make sure the given device is valid */
@ -72,7 +128,7 @@ int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
/* configure UART to 8N1 mode */
dev[uart]->CSRC = (1 << UCSZ00) | (1 << UCSZ01);
/* set clock divider */
dev[uart]->BRR = CLOCK_CORECLOCK / (16 * baudrate);
_set_brr(uart, baudrate);
/* enable RX and TX and the RX interrupt */
dev[uart]->CSRB = ((1 << RXCIE0) | (1 << RXEN0) | (1 << TXEN0));
@ -82,7 +138,7 @@ int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
void uart_write(uart_t uart, const uint8_t *data, size_t len)
{
for (size_t i = 0; i < len; i++) {
while (!(dev[uart]->CSRA & (1 << UDRE0)));
while (!(dev[uart]->CSRA & (1 << UDRE0))) {};
dev[uart]->DR = data[i];
}
}