FWIW I've attached my example code, I would be interested to know if this
works for others. The make file if you are in the libopencm3 examples tree
is simply
OBJ = clock.o
BINARY = usart-irq
LDSCRIPT = ../stm32f4-discovery.ld
include ../../Makefile.include
I've run it both under gdb and not under a debugger and when you type ^C it
prints the 'I' (which was my proof that it was taking the branch) and then
hangs forever.
--Chuck
/* vim: set noexpandtab ts=4 :
* This file is part of the libopencm3 project.
*
* Copyright (C) 2013 Chuck McManis <cmcma...@mcmanis.com>
*
* This library is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This library 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* USART example (alternate console)
*
* This version then adds in interrupts, which is really handy for
* the receive function as it is impossible to predict when someone
* might type a character, further you can create a "character based
* reset" capability if you choose to.
*/
#include <stdint.h>
#include <libopencm3/stm32/gpio.h>
#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/usart.h>
#include <libopencm3/cm3/nvic.h>
#include <libopencm3/stm32/iwdg.h>
#include <libopencm3/cm3/scb.h>
#include "clock.h"
/*
* Some definitions of our console "functions" attached to the
* USART.
*
* These define sort of the minimum "library" of functions which
* we can use on a serial port. Note that the definitions are
* the same as they are if the console is implemented by the USB
* CDC device as well (see ../usb-serial)
*/
#define CONSOLE_UART USART2
void console_putc(char c);
char console_getc(int wait);
void console_puts(char *s);
int console_gets(char *s, int len);
/* this is for fun, if you type ^C to this example it will reset */
#define RESET_ON_CTRLC
/* This is a ring buffer to holding characters as they are typed
* it maintains both the place to put the next character received
* from the UART, and the place where the last character was
* read by the program. See the README file for a discussion of
* the failure semantics.
*/
#define RECV_BUF_SIZE 128 // Arbitrary buffer size
char recv_buf[RECV_BUF_SIZE];
volatile int recv_ndx_nxt; // Next place to store
volatile int recv_ndx_cur; // Next place to read
/* For interrupt handling we add a new function which is called
* when recieve interrupts happen. The name (usart2_isr) is created
* by the irq.json file in libopencm3 calling this interrupt for
* USART2 'usart2', adding the suffix '_isr', and then weakly binding
* it to the 'do nothing' interrupt function in vec.c.
*
* By defining it in this file the linker will override that weak
* binding and instead bind it here, but you have to get the name
* right or it won't work. And you'll wonder where your interrupts
* are going.
*/
void usart2_isr(void) {
uint32_t reg;
int i;
do {
reg = USART_SR(CONSOLE_UART);
if (reg & USART_SR_RXNE) {
recv_buf[recv_ndx_nxt] = USART_DR(CONSOLE_UART);
#ifdef RESET_ON_CTRLC
/* Check for "reset" */
if (recv_buf[recv_ndx_nxt] == '\003') {
/* reset the system */
console_putc('I');
scb_reset_system();
while(1) ;
}
#endif
/* Check for "overrun" */
i = (recv_ndx_nxt + 1) % RECV_BUF_SIZE;
if (i != recv_ndx_cur) {
recv_ndx_nxt = i;
}
}
} while ((reg & USART_SR_RXNE) != 0); // can read back-to-back interrupts
}
/*
* console_putc(char c)
*
* Send the character 'c' to the USART, wait for the USART
* transmit buffer to be empty first.
*/
void console_putc(char c) {
uint32_t reg;
do {
reg = USART_SR(CONSOLE_UART);
} while ((reg & USART_SR_TXE) == 0);
USART_DR(CONSOLE_UART) = (uint16_t) c & 0xff;
}
/*
* char = console_getc(int wait)
*
* Check the console for a character. If the wait flag is
* non-zero. Continue checking until a character is received
* otherwise return 0 if called and no character was available.
*
* The implementation is a bit different however, now it looks
* in the ring buffer to see if a character has arrived.
*/
char console_getc(int wait) {
char c = 0;
while ((wait != 0) && (recv_ndx_cur == recv_ndx_nxt)) ;
if (recv_ndx_cur != recv_ndx_nxt) {
c = recv_buf[recv_ndx_cur];
recv_ndx_cur = (recv_ndx_cur + 1) % RECV_BUF_SIZE;
}
return c;
}
/*
* void console_puts(char *s)
*
* Send a string to the console, one character at a time, return
* after the last character, as indicated by a NUL character, is
* reached.
*/
void console_puts(char *s) {
while (*s != '\000') {
console_putc(*s);
/* Add in a carraige return, after sending line feed */
if (*s == '\n') {
console_putc('\r');
}
s++;
}
}
/*
* int console_gets(char *s, int len)
*
* Wait for a string to be entered on the console, limited
* support for editing characters (back space and delete)
* end when a <CR> character is received.
*/
int console_gets(char *s, int len) {
char *t = s;
char c;
*t = '\000';
/* read until a <CR> is received */
while ((c = console_getc(1)) != '\r') {
if ((c == '\010') || (c == '\127')) {
if (t > s) {
/* send ^H ^H to erase previous character */
console_puts("\010 \010");
t--;
}
} else {
*t = c;
console_putc(c);
if ((t - s) < len) {
t++;
}
}
/* update end of string with NUL */
*t = '\000';
}
return (t - s);
}
/*
* Set up the GPIO subsystem with an "Alternate Function"
* on some of the pins, in this case connected to a
* USART.
*/
int main(void) {
char buf[128];
int len;
clock_setup(); // initialize our clock
/* MUST enable the GPIO clock in ADDITION to the USART clock */
rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPDEN);
/* This example uses PD5 and PD6 for Tx and Rx respectively
* but other pins are available for this role on USART2 (our chosen
* USART) as well, such as PA2 and PA3. You can also split them
* so PA2 for Tx, PD6 for Rx but you would have to enable both
* the GPIOA and GPIOD clocks in that case
*/
gpio_mode_setup(GPIOD, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO5 | GPIO6);
/* Actual Alternate function number (in this case 7) is part
* depenedent, check the data sheet for the right number to
* use.
*/
gpio_set_af(GPIOD, GPIO_AF7, GPIO5 | GPIO6);
/* This then enables the clock to the USART2 peripheral which is
* attached inside the chip to the APB2 bus. Different peripherals
* attach to different buses, and even some UARTS are attached to
* APB1 and some to APB2, again the data sheet is useful here.
*/
rcc_peripheral_enable_clock(&RCC_APB1ENR, RCC_APB1ENR_USART2EN);
/* Set up USART/UART parameters using the libopencm3 helper functions */
usart_set_baudrate(CONSOLE_UART, 115200);
usart_set_databits(CONSOLE_UART, 8);
usart_set_stopbits(CONSOLE_UART, USART_STOPBITS_1);
usart_set_mode(CONSOLE_UART, USART_MODE_TX_RX);
usart_set_parity(CONSOLE_UART, USART_PARITY_NONE);
usart_set_flow_control(CONSOLE_UART, USART_FLOWCONTROL_NONE);
usart_enable(CONSOLE_UART);
/* Enable interrupts from the USART */
nvic_enable_irq(NVIC_USART2_IRQ);
/* Specifically enable recieve interrupts */
usart_enable_rx_interrupt(CONSOLE_UART);
/* At this point our console is ready to go so we can create our
* simple application to run on it.
*/
console_puts("\nUART Demonstration Application\n");
#ifdef RESET_ON_CTRLC
console_puts("Press ^C at any time to reset system.\n");
#endif
while (1) {
console_puts("Enter a string: ");
len = console_gets(buf, 128);
if (len) {
console_puts("\nYou entered : '");
console_puts(buf);
console_puts("'\n");
} else {
console_puts("\nNo string entered\n");
}
}
}
/* vim: set noexpandtab ts=4 :
* This file is part of the libopencm3 project.
*
* Copyright (C) 2013 Chuck McManis <cmcma...@mcmanis.com>
*
* This library is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This library 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* Now this is just the clock setup code from systick-blink as it is the
* transferrable part.
*/
#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/gpio.h>
#include <libopencm3/cm3/nvic.h>
#include <libopencm3/cm3/systick.h>
/* Common function descriptions */
#include "clock.h"
/* milliseconds since boot */
static volatile uint32_t system_millis;
/* Called when systick fires */
void sys_tick_handler(void) {
system_millis++;
}
/* simple sleep for delay milliseconds */
void msleep(uint32_t delay) {
uint32_t wake = system_millis + delay;
while (wake > system_millis) ;
}
/* Getter function for the current time */
uint32_t mtime(void) {
return system_millis;
}
/*
* clock_setup(void)
*
* This function sets up both the base board clock rate
* and a 1khz "system tick" count. The SYSTICK counter is
* a standard feature of the Cortex-M series.
*/
void clock_setup(void)
{
/* Base board frequency, set to 168Mhz */
rcc_clock_setup_hse_3v3(&hse_8mhz_3v3[CLOCK_3V3_168MHZ]);
/* clock rate / 168000 to get 1mS interrupt rate */
systick_set_reload(168000);
systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);
systick_counter_enable();
/* this done last */
systick_interrupt_enable();
}
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