Display stops responding above 32 byte writes

[andrewcharnley]

More than 32 characters crashes the display. I've not had a chance to investigate further but it is consistent. This is a problem for those of us doing DMA writes of the entire screen.

[nseidle]

Sorry, I need to get an issue template on this repo:

What micro or processor are you using to drive the display? What interface (I2C, serial, or SPI)? What driver (our Arduino library, probably your own)?

Code to replicate the issue would be immensely helpful.

Can you be more specific about the crash? Unit freezes until power cycle, unit displays garbage, etc.

I suspect you're hitting the 32 byte I2C buffer limit used in Arduino (the limit is in our peripheral. Not knowing your setup I can only guess that you might as well). Again, without knowing how you're interfacing to the display, I'm really just guessing.

[andrewcharnley]

Sounds plausable. I2C using a NRF52.

I work around it by DMA'ing a row in 4 goes with a timer and counter. You should be able to easily replicate it, just write/print more than a line (line and a half will do it) and the display will lock up.

[nseidle]

What is the size of the I2C buffer on nRF52?

I can replicate with an Artemis. Unit stops responding to I2C commands until power cycle.

 lcd.print("1234567890123456789012345678901"); //Good
//lcd.print("12345678901234567890123456789012"); //Good
//lcd.print("123456789012345678901234567890123"); //Good
//lcd.print("1234567890123456789012345678901234"); //Fails

Curiously 33 bytes works. It's not immediately clear to me why the I2C ISR is going off into never never land but I do believe it's Arduino core / I2C 32 byte buffer related.

Thanks for reporting. We won't be hacking the arduino core to support larger I2C buffers. For now your best solution is to limit your writes to 32 bytes. Let me know if you're using our Arduino library. If you are, we can modify the write function to break large transfers into I2C buffer sized chunks.

[andrewcharnley]

I generally use Arduino as a last resort, but since the firmware is embedded I don't see why you can't implement and include a patch file (in the rare case someone really wants to apply it manually). Personally I just want it working out the box, which I guess is the same for most people. Is the 32 byte referring to the circular buffer? I believe the Arduino is servicing the I2C buffer by interrupt but my experience with the HD controller used in the display is it uses a 50us delay between characters, so it's probably a race between completing those and the buffer filling up at 100kbs.

The I2C buffer on the NRF52 is limited only by RAM as it's DMA based. I wired up a timer to write chucks of 20 bytes one after the other with a little delay to allow the display/arduino code to recover. It works well enough.

[fourstix]

I believe the 32 byte limitation is a limitation of the Wire library.