Fix stopBit = false mode in nRF51 Wire library

[dsanders11]

The changes in #137 don't work with trying to use stopBit = false. Minor change to allow doing a requestFrom in multiple parts. This is necessary due to limited buffer sizes.

Example usage of what this allows (which doesn't currently work):

uint8_t buffer[20];

Wire.requestFrom(address, 10, false);
for (uint8_t i=0; i < 10; i++) {
    buffer[i] = Wire.read();
}

// Do something else, then finish reading

Wire.requestFrom(address, 10);
for (uint8_t i=0; i < 10; i++) {
    buffer[10 + i] = Wire.read();
}

@carlosperate, any thoughts on this PR? It's tested and works, but it's kind of quick and dirty as I needed it working ASAP.

[dlabun]

@sandeepmistry Do you think this is a serious enough issue to include in v0.4.0?

[sandeepmistry]

@dlabun yes, I think so.

@dsanders11 thanks for submitting! Do we need a similar change for endTransmission(bool stopBit)?
Apart from that, your changes look good to me (although I haven't tried them on a physical board yet).

[dsanders11]

@sandeepmistry, probably needed in endTransmission(bool stopBit) as well, yea. I'm testing this on the nRF52832 Breakout Board from Sparkfun, and using Wire_nRF51.cpp despite it being nRF52 since that file was most recently improved and fixed, and works just fine since that API is available on nRF52. These changes could be applied to Wire_nRF52.cpp as well, but that file is still using the interrupt version which Wire_nRF51.cpp switched off of, so it may not cleanly apply.

[sandeepmistry]

Ok, this looks good to me!

I've tested with the micro:bit:

#include <Wire.h>

void setup() {
  Serial.begin(9600);
  Wire.begin();

  int address = 0x0E;

  Wire.beginTransmission(address);
  Wire.write(0x11);
  Wire.write(0x0f);
  Wire.endTransmission(false);

  Wire.beginTransmission(address);
  Wire.write(0x11);
  Wire.write(0x0e);
  Wire.endTransmission(false);

  Wire.beginTransmission(address);
  Wire.write(0x11);
  Wire.endTransmission();

  Serial.println("requestFrom false");
  Serial.println(Wire.requestFrom(address, 1, false));
  Serial.println((byte)Wire.read(), HEX);

  Serial.println("requestFrom true");
  Serial.println(Wire.requestFrom(address, 1, true));
  Serial.println((byte)Wire.read(), HEX);

  Serial.println("done");
}

void loop() {
}

It was a built-in MAG3110 compass sensor on I2C address 0x0E. Without these changes the sketch hangs, with them it works!

I haven't used a logic analyzer, but a TX with stop bits seems to work as is.

[sandeepmistry]

@dsanders11 thanks!

It would be awesome if you could spend some time on seeing what's wrong with the nRF52 Wire file. Maybe a combination of this PR and #137 need to be applied?