Bus_Parallel8/16 (ESP32-S3): never queue a zero-length DMA chunk - #332
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The copy path splits a transfer into chunks whose first four bytes go out as LCD command cycles and the rest by DMA. For some lengths (for example 257 to 260 bytes) a chunk was only four bytes long, so the DMA descriptor had no payload; Bus_Parallel16 then waited forever for its TX FIFO to fill. These lengths reach the copy path more often now that DMA-inaccessible sources are copied. Bus_Parallel16 now fills each chunk up to the buffer size (one byte less when a byte is pending from an odd length) and sends a five-byte remainder as four command bytes plus the pending byte. Bus_Parallel8 enlarges a four-byte chunk so that it carries a payload.
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Brings the ESP32-S3 parallel bus fix of 0.2.32 (#330) to develop.
The copy path of
Bus_Parallel8/Bus_Parallel16on the ESP32-S3 splits a transfer into chunks whose first four bytes go out as LCD command cycles and the rest by DMA. For some lengths (for example 257 to 260 bytes, or 5 bytes with no pending byte) a chunk was only four bytes long, so the DMA descriptor had no payload;Bus_Parallel16then waited forever for its TX FIFO to fill. DMA-inaccessible sources (#324) take this path, so the lengths are reached more often.Bus_Parallel16fills each chunk up to the buffer size (one byte less when a byte is pending from an odd length) and sends a five-byte remainder as four command bytes plus the pending byte.Bus_Parallel8enlarges a four-byte chunk so that it carries a payload.Checked on the host by running the chunking code over every length from 1 to 2000 (and both pending-byte states for
Bus_Parallel16) under ASan / UBSan: every DMA payload is non-empty and stays within the buffer.