Software serial query

paulskirk53 · February 1, 2021, 9:54pm

I am using an atmega328p chip and need two extra serial ports, so was thinking to use a software serial library such as the arduino software serial. So my question is: is it possible to use the Arduino softwareSerial outside of the Arduino coding environment, and if so, how would I set this up in platformio?

If not the arduino softwareserial, is there a different serial library which could provide two extra ports (they’re not used simultaneously).

I’ve programmed arduino for a few years, but now looking to program the 328 without the arduino platform.

thanks for help,
Paul

maxgerhardt · February 1, 2021, 10:04pm

A bit of googling turns up the project GitHub - blalor/avr-softuart: Software UART implementation for the AVR platform which supports ATMega328P chips. The implementation is just two files, softuart.c and .h. It has code to support one further serial port at PD1 and PD2 (configurable though), but not two, and uses up the TIM0_COMPA_vect interrupt, so TIM0 is used for that. So you have to slightly re-code it. If the two software UARTs are never used at the same time, you might get away with just making some constants to variables, e.g. regarding the pin and port macros, and exchange their value at the right time in the code.

Otherwise, rewrite ArduinoCore-avr/libraries/SoftwareSerial/src at master · arduino/ArduinoCore-avr · GitHub to not use Arduino functions (or copy the needed ones into the code). From what I see it just uses some conversion functions like digitalPinToPort to map a pin number to the needed port and pin register macros, and a digitalWrite and pinMode. You can substitute that with your implementation or copy the Arduino one.

normandunbar · February 1, 2021, 10:22pm

Unfortunately, it also does using Print::write which is the Arduino class that provides all the serial output stuff.

That might be a pain to rewrite.

Cheers,
Norm.

maxgerhardt · February 1, 2021, 10:25pm

Hmm the way I see it it does that to auto-include the other implementations of the Print class which do e.g. a write with a buffer. The class then does however only implement the fundamental primitive, the write-single-byte, which all other derivatives use

github.com

arduino/ArduinoCore-avr/blob/9f8d27f09f3bbd1da1374b5549a82bda55d45d44/libraries/SoftwareSerial/src/SoftwareSerial.cpp#L415-L416


      
          size_t SoftwareSerial::write(uint8_t b)

          {

github.com

arduino/ArduinoCore-avr/blob/9f8d27f09f3bbd1da1374b5549a82bda55d45d44/cores/arduino/Print.h#L51-L59


      
          virtual size_t write(uint8_t) = 0;
          size_t write(const char *str) {
            if (str == NULL) return 0;
            return write((const uint8_t *)str, strlen(str));
          }
          virtual size_t write(const uint8_t *buffer, size_t size);
          size_t write(const char *buffer, size_t size) {
            return write((const uint8_t *)buffer, size);
          }

github.com

arduino/ArduinoCore-avr/blob/9f8d27f09f3bbd1da1374b5549a82bda55d45d44/cores/arduino/Print.cpp#L33-L42


      
          /* default implementation: may be overridden */
          size_t Print::write(const uint8_t *buffer, size_t size)
          {
            size_t n = 0;
            while (size--) {
              if (write(*buffer++)) n++;
              else break;
            }
            return n;
          }

So that should not be the dealbreakinger, since it’s not calling into implementations of the Print::write functions – it implements them.

normandunbar · February 2, 2021, 6:21am

Ah, yes, of course. Bit of a brain fadebthere I think, sorry.

Thank @maxgerhardt.

Cheers,
Norm.

paulskirk53 · February 2, 2021, 11:06am

thanks for replies. I might be better off finding a pin compatible chip which has two uarts perhaps. I could use spi as one of the three comm links I need.

Paul

paulskirk53 · February 2, 2021, 11:25am

is there a good place to look for pin compatible alternatives? I found 328PB which has 2 uarts, but as far as I can find googling its not available as a dip…

Perhaps there’s a features comparison site?? I’ll see what I can find.
thanks
Paul

schallbert · February 2, 2021, 9:56pm

Just had a quick look at the files (I started programming Attiny82 years ago before switching to the Arduino framework. In the End, I converted to follow the Arduino road, saving myself from re-writing libraries to my special application all the time…). Max’ choice looks like it would be working pretty much out of the box for you. All you need to do, is to wrap the contents in two classes (one “worker class” which does the bit-banging and one “config” class where you’ll finally construct the objects with…) But be reminded that this will be some evenings worth of work; if you want to go down that path, off you go