LPUART causing deadlock

[Chris H]

Hi guys,

I am experiencing some issues with the LPUART implementation: it seems that when using the setup with hci_lpuart (with LE Coded PHY) bluetooth connection isn't stable. Every now and then the whole program stops working either when connecing to a remote BLE device or when discovering a device' services and characteristics. Like there is a deadlock, because other threads don't get scheduled anymore. And its random. Sometimes it works (connection establishment, service discovery, data transmission), sometimes there is this deadlock situation. From reading the (program specific) logs I guess that a callback isn't responding as expected, but that is just a guess. I am not having this issue with the regular hci_uart connection.

The setup I am using:

• Actinius Icarus (nRF9160) connected via lp_uart to
• Particle Xenon (nRF52840) running hci_lpuart (with additional settings for LE Coded PHY)
• nRF Connect SDK v1.5.1
• LE Coded PHY enabled
• 115200 baud rate (happens also with 1000000 baud rate).

Any suggestion what triggers this issue?

Kind regards!
Christian

[Krzysztof Chruscinski]

Hi,

the problem is with GPIOTE interrupt level, by default zephyr is using level 5 for it and `NRF_DEFAULT_IRQ_PRIORITY` for others. There is no clear reason for that but it's just been like this for ages. Low power UART assumes that GPIOTE and UARTE interrupts are on the same level and have no protection mechanisms. There is PR with fixes for that https://github.com/nrfconnect/sdk-nrf/pull/4418.

You can try to apply overlay change in hci_lpuart app https://github.com/nrfconnect/sdk-nrf/pull/4418/commits/4dc8fc024d318c47d7c66abc070a513fff846af6

And similar change in nrf9160ns application: github.com/.../267f4410eaecc870e08bc6c1b0cb00b8fd20bc63

[Simon]

Check out this PR as well https://github.com/zephyrproject-rtos/zephyr/pull/36366, which should make LPUART more stable.

[Chris H]

Hi,

thank you very much for answering! It seems to work stable with the version you provided, but anyway I will also try the version with the pullups added.

Kind regards,
Christian