nrf52840 SPI clock line contention causing SPI driver to hang

RE: nrf52840 SPI clock line contention causing SPI driver to hang

droberson — Thu, 23 Aug 2018 18:48:13 GMT

Thanks for the feedback! I will implement some sort of timer interrupt to power cycle the SPI peripheral in case this happens again.

RE: nrf52840 SPI clock line contention causing SPI driver to hang

droberson — Thu, 23 Aug 2018 18:43:17 GMT

Daniel,

Unfortunately I do not have captures of my SPI clock waveforms. I was still seeing the clock line toggling but the voltage range was 0V to something small like 50 mV.

RE: nrf52840 SPI clock line contention causing SPI driver to hang

awneil — Thu, 23 Aug 2018 15:33:15 GMT

[quote userid="73492" url="~/f/nordic-q-a/37732/nrf52840-spi-clock-line-contention-causing-spi-driver-to-hang"]Should there be some sort of safety timeout here? [/quote]

Not really.

In SPI, the Clock line should only ever be driven by the master - never by any slave.

RE: nrf52840 SPI clock line contention causing SPI driver to hang

Kenneth — Thu, 23 Aug 2018 12:58:39 GMT

Hi,

This is due to internal design. In short:

The clock line is looped back through the pin to the SPI peripheral to ensure that timing of MISO and MOSI are identical, as a side effect this also means that the internal circuitry will not see the clock if the pin is forced low externally, and thereby "hang" until valid clock is present. I guess a serial resistor on the clock line could solve this and/or start an timer that can timeout and application can power cycle the SPI peripheral to recover.

Best regards,
Kenneth

RE: nrf52840 SPI clock line contention causing SPI driver to hang

Daniel Sullivan — Wed, 22 Aug 2018 22:50:06 GMT

Just a note to add to this: I've also had this same issue when using an external SPI display. When the display was connected incorrectly and its own MCU wasn't booting correctly, it would load the SPI lines in strange ways causing transfers to fail / the driver to stop in the same place.

droberson: Do you have a logic analyser result you can add to this post? I was finding very long rise times when SPI was being held down by the peripheral.