[riot-notifications] [RIOT-OS/RIOT] drivers/cc2538_rf: fix deadlock when receiving too fast. (#16716)

José Alamos notifications at github.com
Mon Aug 9 11:53:55 CEST 2021


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### Contribution description
This PR fixes a deadlock in `cc2538_rf` caused by frames being received too fast.
The reasons for this deadlock are:
1. While sending with CCA the RX chain should be disabled, which was not the case. When frames were received during CCA, there was a wrong state transition in the `submac` that ended with `submac->tx`  being not released. Therefore, the `submac` would always return `-EBUSY`.
2. The driver logic was always following the internal FSM states, although the Reference Manual (Section 23.11) explicitly says to not do that:

> Although it is possible to read the state of the FSM, do not use this information to control the program flow
in the application software

I was able to trigger cases were the FSM state was not defined but the radio was still fully functional. Therefore, I think we should follow the datasheet here.

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### Testing procedure
It's very hard to reproduce, but here's a way: Take a RIOT BR, a `cc2538_rf` and another node (I used a `nrf52840dk`). When all nodes get prefix, ping from the CC2538 to the other non-BR node (use 1024 kB and short intervals such as 200 ms). Every now and then reset the target node. At some point, the `cc2538_rf` won't be able to send more frames and the TX counter will be increasing non-stop, although no frames get out of the radio. The pktbuf will be full of garbage frames.

With this PR, it's not possible to reproduce this scenario.
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### Issues/PRs references
None so far.
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You can view, comment on, or merge this pull request online at:

  https://github.com/RIOT-OS/RIOT/pull/16716

-- Commit Summary --

  * drivers/cc2538_rf: disable RX detection during CCA
  * drivers/cc2538_rf: don't poll internal FSM state

-- File Changes --

    M cpu/cc2538/include/cc2538_rf.h (2)
    M cpu/cc2538/radio/cc2538_rf_radio_ops.c (61)

-- Patch Links --

https://github.com/RIOT-OS/RIOT/pull/16716.patch
https://github.com/RIOT-OS/RIOT/pull/16716.diff

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