-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 18.04.2014 09:49, Maarten Brock wrote: > Hello Georg, > > Is this behaviour true for all 16 bit SFR's? Or is it different for > every other SFR? If it's always the same then maybe SDCC could take > this into account. > > Maarten > >> hi all, >> >> it might be common knowledge in the community, but it sure was >> new to me (and took me some time to debug)… >> >> As you know the STM8 is and 8-bit uC, so reading from or writing >> to 16b peripheral registers (SFR) takes place in 2 steps. And I >> found that the sequence of access matters for 16b peripheral >> registers (SFR), and is different for read and write: write: >> byteH+byteL is ok, but byteL+byteH (or word write in C) fails >> read: byteL+byteH (and word read in C) is ok, but byteH+byteL >> fails >> >> I observed this behavior for SDCC v3.4 RC2, and also for Cosmic >> C-compiler 4.3.7. Hope this note helps avoiding bugs, and saving >> debugging time.
For which sfrs did you test? >> Have a nice day, :-) Georg > Unfortunately, AFAIK, this is not the same for all 16-bit sfrs. In particular, some of the timer-related registers we always need to access the high byte first, followed by the low byte (both on reads and write): Examples from the STM8L101: For the TIM_CNTR register, the high byte must be read first, followed by the low byte. For the TIM_AAR register, the high byte must be written first, followed by the low byte. But I think it is only the timer registers that are high byte first. Philipp P.S.: If we can, we often want to read / write the low byte first, since ldw is faster than to ld, and ldw reads / writes the low byte first. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Icedove - http://www.enigmail.net/ iEYEARECAAYFAlNQ/qIACgkQbtUV+xsoLprUBwCfUUh7FOFi2ZIEXKlVCMAII6+u VWQAnRZQxexrultGGmr3UYDlC+IF7Cq3 =/xOR -----END PGP SIGNATURE----- ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. Written by three acclaimed leaders in the field, this first edition is now available. Download your free book today! http://p.sf.net/sfu/NeoTech _______________________________________________ Sdcc-user mailing list Sdcc-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/sdcc-user
