nrf52840 serial

If I put too many characters into a serial using IRQ mode, it stops reading input.

I haven't tried polling or DMA yet.


  • nRF5_SDK_15.0.0_a53641a
  • gcc-arm-none-eabi 6.3.1 and I also tried segger
  • nRF52840-DK with a PCA10056 1.0.0
  • examples/peripheral/serial.

I can't get the onboard USB serial to work with flow control enabled(works with it disabled), so I'm doing testing with an FTDI breakout.

The serial example works consistently and correctly if I just type characters on the keyboard, but if I paste a chunk of text larger than 47 characters, the serial port reads between 20 and 40 characters, and then stops reading.

If I connect  a gps unit that emits NMEA sentences, it will read some of them, and then stop reading. ~47 characters every second, and it was getting like 3-10 seconds.

Looking at what it does with gdb (I have not yet followed too closely) it seems that nrf_serial_read function just returns nothing, and everything else keeps working.

It does this with and without the hardware flow control.

I tried increasing the buffer size, but it didn't seem to change the issue.

If I change the timeout parameter on nrf_serial_read to 0 (as documentation says it really should be in IRQ contexts), it actually reads less characters when you paste data.

Am I using the example wrong, or is this a bug?