[En-Nut-Discussion] SPI MSB/LSB transfers, was Platform independent HD4478

[Uwe Bonnes]

Hi Ole,

    Ole> Hi Uwe, Am 11.09.2014 11:45, schrieb Uwe Bonnes:
    >> The LSB SPI transfer is needed for the LS013.  Thiago, could you
    >> perhaps provide LSB transfer for AVR32?  Any SAM7 user: Does Sam7
    >> allow SPI LSB transfers? A short scan through the AT91SAM7 datasheets
    >> gives me the impression that the SPI peripheral doesn't provide that
    >> capability.

    Ole> If some platform does not provide bit reversal during transfers,
    Ole> how about adding code to do this in software? This would not be
    Ole> very fast, but perhaps should be enough to implement some generic
    Ole> routines for LCDs etc.

Adding such bit reversal code introduces some questions:
- What include file should be used?
- Should the generic code be cycle- or Flash optimized?

Otherwise I noticed all pure SPI mikrocontroller peripherals use MSB
transfers as default. However the STM32 USART in SPI mode send LSB first
with no mean to switch to MSB modes. Ugly...
-- 
Uwe Bonnes                bon at elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
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