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Topic: Arduino Zero - SoftwareSerial library (Read 11650 times) previous topic - next topic


Jan 17, 2017, 06:13 pm Last Edit: Jan 17, 2017, 06:23 pm by MartinL
Hi AloyseTech,

I'm not sure it is possible as is. if you take a look at HardwareSerial.h, you'll see that the 9N1 config doesn't exist.
You're right, I didn't notice that 9 bits worth of data isn't an option in hardware serial.

Although, it might be possible to disable the UART, set the number of bits to 9 and then restart. I haven't tested it though:

Code: [Select]
Serial1.begin(115200);                                          // Set-up Serial1 at 115200bps
while(SERCOM0->USART.SYNCBUSY.bit.ENABLE);                      // Wait for synchronization
SERCOM0->USART.CTRLB.reg |= SERCOM_USART_CTRLB_CHSIZE(1);       // Set CHSIZE to 1 = 9 bits per character
while(SERCOM0->USART.SYNCBUSY.bit.ENABLE);                      // Wait for synchronization


yes, my understanding is that for 9N1, I would have to patch the libraries - those patches exist, but would force me to go back to 1.5.x or I will have to port the patches over. SoftwareSerial is available, just has the dependency on AVR.. Any plans to support ARM targets?


Jan 17, 2017, 11:31 pm Last Edit: Jan 17, 2017, 11:33 pm by MartinL
Hi mzayats,

I believe that a Software Serial library exists for Arduino.org's M0 PRO, (essentially the same as an Arduino Zero). It was included in Arduino.org's IDE from version 1.7.9 onwards: https://github.com/arduino-org/Arduino/releases.

Not sure if it supports 9 bit data, but might be worth a look?


Indeed - https://github.com/arduino-org/Arduino/tree/d110edbbfdf48d1b6ffc116ed1e58e742be4cf6e/hardware/arduino/samd/libraries/SoftwareSerial



Hey guys, So using this arduino.org library I can use software serial on a M0?

I am trying to compile a sketch on a adafruit feather M0, I dont understand enough to be able to port a software serial to an actual hardware serial.

Can can I go about using this arduino.org software serial library?



I needed a serial port for output and the only available pin (PA3) didn't have access to a SERCOM, so I gave the M0 library a shot.  I can confirm that the SoftwareSerial library works on the Zero and its derivatives.

NB: I ran into an error compiling the example sketch:

Code: [Select]
In member function 'void SoftwareSerial::setTX(uint8_t)': ../libraries/SoftwareSerial/SoftwareSerial.cpp:169:25: error: cannot convert 'volatile uint32_t* {aka volatile long unsigned int*}' to 'volatile PORT_OUT_Type*' in assignment
   _transmitPortRegister = portOutputRegister(port);
In member function 'void SoftwareSerial::setRX(uint8_t)':
../libraries/SoftwareSerial/SoftwareSerial.cpp:182:25: error: cannot convert 'volatile uint32_t* {aka volatile long unsigned int*}' to 'volatile PORT_IN_Type*' in assignment
    _receivePortRegister = portInputRegister(port);

The fix for this is to change the following lines in SoftwareSerial.cpp:


Code: [Select]
169:  _transmitPortRegister = portOutputRegister(port);
182:  _receivePortRegister = portInputRegister(port);


Code: [Select]
169:  _transmitPortRegister = (volatile PORT_OUT_Type*)portOutputRegister(port);
182:  _receivePortRegister = (volatile PORT_IN_Type*)portInputRegister(port);

This allows the arduino.cc IDE to process the library files and then the examples all work fine.  I have confirmed it working at 31250 baud for MIDI, I can only imagine that it would also work at other baud rates.

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