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Diffstat (limited to 'Documentation/blackfin/bfin-spi-notes.txt')
| -rw-r--r-- | Documentation/blackfin/bfin-spi-notes.txt | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/Documentation/blackfin/bfin-spi-notes.txt b/Documentation/blackfin/bfin-spi-notes.txt new file mode 100644 index 00000000..eae6eaf2 --- /dev/null +++ b/Documentation/blackfin/bfin-spi-notes.txt @@ -0,0 +1,16 @@ +SPI Chip Select behavior: + +With the Blackfin on-chip SPI peripheral, there is some logic tied to the CPHA +bit whether the Slave Select Line is controlled by hardware (CPHA=0) or +controlled by software (CPHA=1). However, the Linux SPI bus driver assumes that +the Slave Select is always under software control and being asserted during +the entire SPI transfer. - And not just bits_per_word duration. + +In most cases you can utilize SPI MODE_3 instead of MODE_0 to work-around this +behavior. If your SPI slave device in question requires SPI MODE_0 or MODE_2 +timing, you can utilize the GPIO controlled SPI Slave Select option instead. +In this case, you should use GPIO based CS for all of your slaves and not just +the ones using mode 0 or 2 in order to guarantee correct CS toggling behavior. + +You can even use the same pin whose peripheral role is a SSEL, +but use it as a GPIO instead. |