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SPI bit order on Tiva?


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Tracking down the reason why my SHARP Memory LCD library does not work on Tiva and C3200 LaunchPads, I noticed that Energia's SPI.setBitOrder is not implemented for these platforms. Digging a bit deeper (i.e. TivaWare and datasheet) I can't see a register to control SPI bit order.

 

Two questions:

- Did I miss something or does the SSI peripheral not support LSB bit order?

- If not, ARM has an RBIT instruction that would be helpful in a workaround. Any way to invoke this with GCC on a variable without resorting to inline assembly?
 

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Nope, same for Tiva.

 

Energia did not recognize the ARM or CMSIS intrinsics for RBIT and REV, but this works:

asm("rbit %0, %1" : "=r" (rxtxData) : "r" (rxtxData));    // reverse order of 32 bits
asm("rev %0, %1" : "=r" (rxtxData) : "r" (rxtxData));    // reverse order of bytes to get original bits into lowest byte

Will try with CC3200 next and then post a patch to the SPI libraries that emulates bit order.

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