[fpc-pascal] Reversing bit-order of byte
fpascal at brouwerij.homelinux.net
Fri May 4 14:53:24 CEST 2012
On 04-05-12 14:31, Thomas Schatzl wrote:
> It might be good to compile with -Cparmv6 (or -Cparmv7, do not know what
> type the processor you use is), this generates a "better" return
> instruction ("bx lr") - and for the rbit instruction you need armv6
>> Wouldn't it be possible to do
>> rbit r0, r0, lsr #23
>> When reading the ARM programming manual I believe it should.
> No, rbit does not allow the "flexible operand" encoding.
>> But do I gain something ?
> If it were possible, at most a few cpu cycles.
> Compared to the other variants (e.g. with the multiplies, except for the
> table lookup) you already save a lot of cycles - although I guess they
> would be sufficiently fast anyway, considering the typical uart speeds.
My processor flags : -Wpstm32f103rb -Cparmv7m.
The #23 is no typo, I need to reverse 9 bits. I'm using 9 bit
synchronous transmission. My first usart-tests were at 4Mbps. The person
that made the driver recommends max. 6Mbps.
If I need more spare time I'll have to see what DMA can do.
Thanks for all information.
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