uart.c
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/* 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, either version 3 of the License, or
* (at your option) any later version.
*
* 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/>.
*
*/
/* standard libraries */
#include <stdint.h> // standard integer types
#include <stdio.h> // standard I/O facilities
#include <stdlib.h> // general utilities
/* STM32 (including CM3) libraries */
#include <libopencm3/stm32/rcc.h> // real-time control clock library
#include <libopencm3/stm32/gpio.h> // general purpose input output library
#include <libopencm3/stm32/usart.h> // universal synchronous asynchronous receiver transmitter library
#include <libopencm3/cm3/nvic.h> // interrupt handler
#include <libopencmsis/core_cm3.h> // Cortex M3 utilities
#include "uart.h" // UART header and definitions
#include "global.h" // common methods
#define UART_ID 1
#define UART_BAUDRATE 921600
/* output ring buffer, indexes, and available memory */
static volatile uint8_t tx_buffer[64] = {0};
static volatile uint8_t tx_i = 0;
static volatile uint8_t tx_used = 0;
void uart_setup(void)
{
/* enable UART I/O peripheral */
rcc_periph_clock_enable(RCC_USART_PORT(UART_ID)); // enable clock for UART port peripheral
rcc_periph_clock_enable(RCC_USART(UART_ID)); // enable clock for UART peripheral
rcc_periph_clock_enable(RCC_AFIO); // enable pin alternate function (UART)
gpio_set_mode(USART_TX_PORT(UART_ID), GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, USART_TX_PIN(UART_ID)); // setup GPIO pin UART transmit
gpio_set_mode(USART_RX_PORT(UART_ID), GPIO_MODE_INPUT, GPIO_CNF_INPUT_PULL_UPDOWN, USART_RX_PIN(UART_ID)); // setup GPIO pin UART receive
gpio_set(USART_RX_PORT(UART_ID), USART_RX_PIN(UART_ID)); // pull up to avoid noise when not connected
/* setup UART parameters */
usart_set_baudrate(USART(UART_ID), UART_BAUDRATE);
usart_set_databits(USART(UART_ID), 8);
usart_set_stopbits(USART(UART_ID), USART_STOPBITS_1);
usart_set_mode(USART(UART_ID), USART_MODE_TX_RX);
usart_set_parity(USART(UART_ID), USART_PARITY_NONE);
usart_set_flow_control(USART(UART_ID), USART_FLOWCONTROL_NONE);
nvic_enable_irq(USART_IRQ(UART_ID)); // enable the UART interrupt
usart_enable_rx_interrupt(USART(UART_ID)); // enable receive interrupt
usart_enable(USART(UART_ID)); // enable UART
/* reset buffer states */
tx_i = 0;
tx_used = 0;
}
void uart_putchar_blocking(char c)
{
uart_flush(); // empty buffer first
usart_send_blocking(USART(UART_ID), c); // send character
}
void uart_flush(void)
{
while (tx_used) { // idle until buffer is empty
__WFI(); // sleep until interrupt
}
usart_wait_send_ready(USART(UART_ID)); // wait until transmit register is empty (transmission might not be complete)
}
void uart_putchar_nonblocking(char c)
{
while (tx_used>=LENGTH(tx_buffer)) { // idle until buffer has some space
usart_enable_tx_interrupt(USART(UART_ID)); // enable transmit interrupt
__WFI(); // sleep until something happened
}
usart_disable_tx_interrupt(USART(UART_ID)); // disable transmit interrupt to prevent index corruption
tx_buffer[(tx_i+tx_used)%LENGTH(tx_buffer)] = c; // put character in buffer
tx_used++; // update used buffer
usart_enable_tx_interrupt(USART(UART_ID)); // enable transmit interrupt
}
void USART_ISR(UART_ID)(void)
{
if (usart_get_flag(USART(UART_ID), USART_SR_TXE)) { // data has been transmitted
if (!tx_used) { // no data in the buffer to transmit
usart_disable_tx_interrupt(USART(UART_ID)); // disable transmit interrupt
} else {
usart_send(USART(UART_ID),tx_buffer[tx_i]); // put data in transmit register
tx_i = (tx_i+1)%LENGTH(tx_buffer); // update location on buffer
tx_used--; // update used size
}
}
while (usart_get_flag(USART(UART_ID), USART_SR_RXNE)) { // data has been received (repeat while receiving)
char c = usart_recv(USART(UART_ID)); // save character and free UART buffer
user_input_store(c); // store data
}
}
USART_TX_PORT
#define USART_TX_PORT(x)
get port for USART transmit pin based on USART identifier
Definition: global.h:190
RCC_USART
#define RCC_USART(x)
get RCC for USART based on USART identifier
Definition: global.h:184
UART_BAUDRATE
#define UART_BAUDRATE
serial baudrate, in bits per second (with 8N1 8 bits, no parity bit, 1 stop bit settings) ...
Definition: uart.c:43
uart.h
library for UART communication (API)
uart_putchar_blocking
void uart_putchar_blocking(char c)
send character over UART (blocking)
Definition: uart.c:77
USART_ISR
#define USART_ISR(x)
get interrupt service routine for USART based on USART identifier
Definition: global.h:188
RCC_USART_PORT
#define RCC_USART_PORT(x)
get RCC for USART port based on USART identifier
Definition: global.h:206
user_input_store
void user_input_store(char c)
store user input
Definition: global.c:199
uart_putchar_nonblocking
void uart_putchar_nonblocking(char c)
send character over UART (non-blocking)
Definition: uart.c:91
global.h
global definitions and methods (API)
UART_ID
#define UART_ID
USART peripheral.
Definition: uart.c:40
USART_RX_PIN
#define USART_RX_PIN(x)
get pin for USART receive pin based on USART identifier
Definition: global.h:200
USART_TX_PIN
#define USART_TX_PIN(x)
get pin for USART transmit pin based on USART identifier
Definition: global.h:198
USART_IRQ
#define USART_IRQ(x)
get NVIC IRQ for USART based on USART identifier
Definition: global.h:186
USART
#define USART(x)
get USART based on USART identifier
Definition: global.h:182
uart_flush
void uart_flush(void)
ensure all data has been transmitted (blocking)
Definition: uart.c:83
USART_RX_PORT
#define USART_RX_PORT(x)
get port for USART receive pin based on USART identifier
Definition: global.h:192
tx_used
static volatile uint8_t tx_used
how much data needs to be transmitted
Definition: uart.c:48
tx_i
static volatile uint8_t tx_i
current position of transmitted data
Definition: uart.c:47
LENGTH
#define LENGTH(x)
get the length of an array
Definition: global.h:26
tx_buffer
static volatile uint8_t tx_buffer[64]
ring buffer for data to transmit
Definition: uart.c:46
uart_setup
void uart_setup(void)
setup UART peripheral
Definition: uart.c:50