> The following restructuring and optimisations increase the SPI > read performance from 1.3MiB/s (on da850) to 2.87MiB/s (on da830): > > Remove continual revaluation of driver state from the core of the > copy loop. State can not change during the copy loop, so it is > possible to move these evaluations to before the copy loop. > > Cost is more code space as loop variants are required for each set > of possible configurations. The loops are simpler however, so the > extra is only 128bytes on da830 with CONFIG_SPI_HALF_DUPLEX > defined. > > Unrolling the first copy loop iteration allows the TX buffer to be > pre-loaded reducing SPI clock starvation. > > Unrolling the last copy loop iteration removes testing for the > final loop iteration every time round the loop. > > Using the RX buffer empty flag as a transfer throttle allows the > assumption that it is always safe to write to the TX buffer, so > polling of TX buffer full flag can be removed. > > Signed-off-by: Nick Thompson <nick.thomp...@ge.com> > --- > da850 and da830 are similar devices. The SPI module is common to > both, but da850 uses DDR and da830 uses SDRAM. The EVM's might > not actually be comparable, but they appear to be at least similar. > > The speed was tested with a 8MiB transfer from SPI FLASH using: > > sf read 0xc0008000 0 0x800000 > > drivers/spi/davinci_spi.c | 195 +++++++++++++++++++++++++++++-----------
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