[fpc-devel] Problem with bitpacked records and STM32F107 Controller

Sergei Gorelkin sergei_gorelkin at mail.ru
Wed Dec 11 10:03:06 CET 2013

11.12.2013 12:28, Sven Barth пишет:
> Am 11.12.2013 08:43, schrieb Michael Ring:
>> The strb command seems to be the problem, documentation from STM states:
>> Each I/O port bit is freely programmable, however the I/O port registers have to be accessed as
>> 32-bit words (half-word or byte accesses are not allowed).
>> So, is there some way to make the bitset operations word-aligned?
> Better say 32-bit aligned to avoid confusion. Words in Pascal are 16-bit although I know that you
> are talking about the CPUs word size...
>> Are there any good reasons for not doing so?
> What when you really have a byte that you want ot access? Then using 32-bit writes/reads could(*)
> result in unnecessary cycles.
> * I don't know about ARM especially, but I know that for e.g. the m68k a 32-bit store is more
> expensive than a 16-bit or 8-bit store
> That said I don't have a solution for your specific problem except by doing it by hand.
Maybe size of memory access must be guided by size of record? For ARM the record will be 32-bit, and 
for m68k it can be 8 or 16-bit.


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