Arm Mbed and Pelion Device Management support forum

Unable to use SoftSerial or BufferedSoftSerial with stm32f103 (Blue Pill)

Following is the code I’m trying to use:

/**
 * @file    BufferedSoftSerial.cpp
 * @brief   Software Buffer - Extends mbed Serial functionallity adding irq driven TX and RX
 * @author  sam grove
 * @version 1.0
 * @see
 *
 * Copyright (c) 2013
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include "mbed.h"
//K64F
#include<string>
Serial pc(PA_2, PA_3); // tx, rx
#include "BufferedSoftSerial.h"
#include <stdarg.h>

BufferedSoftSerial::BufferedSoftSerial(PinName tx, PinName rx, const char* name)
: SoftSerial(tx, rx, name)
{
SoftSerial::attach(this, &BufferedSoftSerial::rxIrq, SoftSerial::RxIrq);

return;
}

int BufferedSoftSerial::readable(void)
{
return _rxbuf.available();  // note: look if things are in the buffer
}

int BufferedSoftSerial::writeable(void)
{
return 1;   // buffer allows overwriting by design, always true
}

int BufferedSoftSerial::getc(void)
{
return _rxbuf;
}

int BufferedSoftSerial::putc(int c)
{
_txbuf = (char)c;
BufferedSoftSerial::prime();

return c;
}

int BufferedSoftSerial::puts(const char *s)
{
const char* ptr = s;

while(*(ptr) != 0) {
    _txbuf = *(ptr++);
}
_txbuf = '\n';  // done per puts definition
BufferedSoftSerial::prime();

return (ptr - s) + 1;
}

int BufferedSoftSerial::printf(const char* format, ...)
{
char buf[256] = {0};
int r = 0;

va_list arg;
va_start(arg, format);
r = vsprintf(buf, format, arg);
// this may not hit the heap but should alert the user anyways
if(r > sizeof(buf)) {
    error("%s %d buffer overwrite!\n", __FILE__, __LINE__);
}
va_end(arg);
r = BufferedSoftSerial::write(buf, r);

return r;
}

ssize_t BufferedSoftSerial::write(const void *s, size_t length)
{
const char* ptr = (const char*)s;
const char* end = ptr + length;

while (ptr != end) {
    _txbuf = *(ptr++);
}
BufferedSoftSerial::prime();

return ptr - (const char*)s;
}


void BufferedSoftSerial::rxIrq(void)
{
// read from the peripheral and make sure something is available
if(SoftSerial::readable()) {
    _rxbuf = _getc(); // if so load them into a buffer
}

return;
}

void BufferedSoftSerial::txIrq(void)
{
// see if there is room in the hardware fifo and if something is in the software fifo
while(SoftSerial::writeable()) {
    if(_txbuf.available()) {
        _putc((int)_txbuf.get());
    } else {
        // disable the TX interrupt when there is nothing left to send
        SoftSerial::attach(NULL, SoftSerial::TxIrq);
        break;
    }
}

return;
}

void BufferedSoftSerial::prime(void)
{
// if already busy then the irq will pick this up
if(SoftSerial::writeable()) {
    SoftSerial::attach(NULL, SoftSerial::TxIrq);    // make sure not to cause contention in the irq
    BufferedSoftSerial::txIrq();                // only write to hardware in one place
    SoftSerial::attach(this, &BufferedSoftSerial::txIrq, SoftSerial::TxIrq);
}

return;
}


BufferedSoftSerial device(PB_14, PB_15);  // tx, rx

int main() {
device.baud(9600);
while(1) {
    if(pc.readable()) {
        device.putc(pc.getc());
    }
    if(device.readable()) {
        pc.putc(device.getc());
    }
}
}

But, I’m unable to get it work. Can someone please show me a working example.

Hello Kumar,

I not have this board but how I see, you try to use the SoftSerial library.

You can check these topics and maybe you will found the reason.
SoftSerial problem L432KC
TimerEvent behavior is wrong on STM32 Mbed boards

BR, Jan

Thanks Johnny for referring the links.

They are helpful indeed.
Seems like there is certainly some issue with STM regarding SoftSerial.

Regards,
Anurag