nRF52840 (Sense) hangs on this line on the last retry when Trellis isn't connected about adafruit_seesaw

[ladyada]

@hathach will try to replicate when there's some time :) a lot i2c changed recently

[ladyada]

if the i2c is disconnected, it will cause undefined behavior so while this is worth looking at...plz do not disconnect cables :)

[adrienp]

Haha good to know! I just assumed that because of the following code in the basic example I should expect trellis.begin() to return and not hang even if the cable is disconnected, and then print the appropriate message.

  if (!trellis.begin()) {
    Serial.println("Could not start trellis, check wiring?");
    while(1);
  } else {
    Serial.println("NeoPixel Trellis started");
  }

But interesting to know that if i2c is disconnected it could cause undefined behavior, thanks for explaining that!

[hathach]

I will try to reproduce it and post update

[hathach]

@adrienp could you confirm the issue still exists with Arduino IDE and also post your Arduino compile log as attached txt here for analysis. Since I only test and familiar with Arduino, I would like to make sure we are testing with the same setup as well as same version of BSP and used libraries.

[adrienp]

@hathach Yes this issue also exists with Arduino IDE. When the trellis is properly connected, the "basic" example compiles and uploads and I get the expected message NeoPixel Trellis started in the Serial Monitor. When the trellis is not connected, it compiles and uploads, but nothing is printed to the serial monitor because it seems to hang on trellis.begin().
Apologies for the long copy-pastes below, but here's my compile log:

60_upload.txt
60_compile.txt

[hathach]

thank for the confirmation and log, please post it as attached txt, should you have to do it again for readibility.

[hathach]

@adrienp sorry for late response, I got my time to try this out. Device is not actually hanged, the Serial.print() does not appear because of while(1) ; blocking 100% CPU. TinyUSB stack run in the background and requires a delay()/yield() in order to send/receive data from/to USB bus. This is quite typical pitfall when using with TinyUSB. I will update the example to also add delay(1).

Note: You could also force serial immediately by using Serial.flush().

void setup() {
  Serial.begin(9600);
  while(!Serial) delay(1);
  
  if (!trellis.begin()) {
    Serial.println("Could not start trellis, check wiring?");
    while(1) delay(1);
  } else {
    Serial.println("NeoPixel Trellis started");
  }

PS: will be fixed by #62

[adrienp]

Oh wow! Thanks for digging into this and responding @hathach !

[hathach]

no problem at all, I am glad it makes sense to you.