michallenc opened a new pull request, #15801: URL: https://github.com/apache/nuttx/pull/15801
## Summary The message RAM does not behave correctly if lower 16 bits of buffer address overflow (upper 16 bits are set once in matrix driver for the entire CAN driver). For example message RAM starting at `0x2040fc20` would not work for buffers that go beyond `0x20410000` and MCAN would sent data located at `0x20400000` to the network. The same issue would occur even if TX buffers would start directly at `0x20410000`. The upper 16 bits would still have `0x2040` value because of RX buffers located in `0x2040ffff` range. This commit ensures the RAM is always located at the beginning of the data section and thus the overflow mentioned above should never occur. The alternative would be to use larger alignment, but the message RAM can have up to 4352 words and this would cause a significant padding. The RAM is also initialized to zero to ensure valid parity/ECC checksums. The address issue is not described anywhere in the manual, so it is possible this is caused by some incorrect configuration, but the context of the registers looks valid. This commit also fixes the compilation errors when the driver is run without data cache - `MCAN_ALIGN_UP` was undefined. ## Impact This fixes possible faults in SAMv7 MCAN driver. The error occurred only in the situations mentioned above, so it is not easily reproducible. Putting `.mcan` section before `.data` is a better solution than bigger alignment, as it avoids unnecessary padding and RAM usage. This also fixes compile errors when the driver is run without data cache - `MCAN_ALIGN_UP` was undefined. ## Testing Tested on SAMv7 custom board. Before the fix, I had two TX buffers inside `0x2040ffff` range and two inside `0x2041ffff` range. The first two buffers worked as expected, but other two took data from `0x20400000` address instead of `0x20410000`. Locating the message RAM at the beginning of `.data` section solves this as overflow can never occur. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: commits-unsubscr...@nuttx.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
