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authorMarek Vasut <marex@denx.de>2012-08-31 16:08:00 +0000
committerStefano Babic <sbabic@denx.de>2012-09-06 14:17:55 +0200
commite9f7eafd3cc932d5d6e7e8acd96d5f15679e4a86 (patch)
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MX28: SPI: Fix the DMA chaining
It turns out that in order for the SPI DMA to properly support continuous transfers longer than 65280 bytes, there are some very important parts that were left out from the documentation. Firstly, the XFER_SIZE register is not written with the whole length of a transfer, but is written by each and every chained descriptor with the length of the descriptors data buffer. Next, unlike the demo code supplied by FSL, which only writes one PIO word per descriptor, this does not apply if the descriptors are chained, since the XFER_SIZE register must be written. Therefore, it is essential to use four PIO words, CTRL0, CMD0, CMD1, XFER_SIZE. CMD0 and CMD1 are written with zero, since they don't apply. The DMA programs the PIO words in an incrementing order, so four PIO words. Finally, unlike the demo code supplied by FSL, the SSP_CTRL0_IGNORE_CRC must not be set during the whole transfer, but it must be set only on the last descriptor in the chain. Signed-off-by: Marek Vasut <marex@denx.de> Cc: Fabio Estevam <festevam@gmail.com> Cc: Otavio Salvador <otavio@ossystems.com.br> Cc: Stefano Babic <sbabic@denx.de>
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