cpu/stm32: Fix reception bug in periph_eth [backport] #15319
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This backport only contains the second commit of #15318, the improved debug output is not relevant for the bug fix. |
The reception code hands RX DMA descriptors back to the DMA right after its contents were copied into the network stack internal buffer. This increases the odds that the DMA never runs out of DMA descriptors to fill, even under high load. However, the loop fetching the Ethernet frame stops to iterate at the end of the frame. If the DMA used one more descriptor to store the FCS, this was not returned back to the DMA. This commit fixes it.
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This PR fixes the issue I had. Using scapy I tested:
and all from 14 to 1500 byte in framesize adressing 3 different destinations that are all received by the node
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Partial backport of "cpu/stm32: Fix reception bug in periph_eth #15318"
Contribution description
The reception code hands RX DMA descriptors back to the DMA right after its contents were copied into the network stack internal buffer. This increases the odds that the DMA never runs out of DMA descriptors to fill, even under high load. However, the loop fetching the Ethernet frame stops to iterate at the end of the frame. If the DMA used one more descriptor to store the FCS, this descriptor was not returned back to the DMA.
Testing procedure
Send an Ethernet frame that has a size n in bytes with n % 256 > 252, e.g. 765 bytes. In master, the driver will stop receiving frames after one such frame. E.g.
produces an Ethernet frame of the correct size for me. With this PR, the issue is fixed.
Issues/PRs references
Reported by @kfessel via email.