epicsMMIO.h macrized ioread causes multiple accesses

[mdavidsaver]

Andrew Johnson and Shifu Xu of ANL report a nasty bug with epicsMMIO.h effecting all targets except RTEMS/powerpc. This is known to cause incorrect behavior with mrfioc2 on vxWorks, though this particular issue won't manifest on other targets.

On 07/01/2016 05:51 PM, Andrew Johnson wrote:
> ...
> Register reads from the MRF230 are done by calling READ32.
>
> In mrfCommonIO.h:
>
> #define READ32(base,offset) NAT_READ32(base,offset)
> #define NAT_READ32(base,offset) \
> nat_ioread32 ((epicsUInt8 *)(base) + U32_ ## offset)
>
> In epicsMMIO.h:
>
> #define nat_ioread32(address) bswap32(sysPciInLong((UINT32 *)(address)))
>
> For a PowerPC:
>
> #define bswap32(value) ( \
> (((epicsUInt32)(value) & 0x000000ff) << 24) | \
> (((epicsUInt32)(value) & 0x0000ff00) << 8) | \
> (((epicsUInt32)(value) & 0x00ff0000) >> 8) | \
> (((epicsUInt32)(value) & 0xff000000) >> 24))
>
> Expanding out the bswap32() macro in nat_ioread32 results in
>
> #define nat_ioread32(address) ( \
> (((epicsUInt32)(sysPciInLong((UINT32 *)(address))) & 0x000000ff) <<
> 24) | \
> (((epicsUInt32)(sysPciInLong((UINT32 *)(address))) & 0x0000ff00) << 8) | \
> (((epicsUInt32)(sysPciInLong((UINT32 *)(address))) & 0x00ff0000) >> 8) | \
> (((epicsUInt32)(sysPciInLong((UINT32 *)(address))) & 0xff000000) >> 24))
>
> i.e. four actual reads for every call to READ32. If the register is a
> FIFO, that's probably going to throw away entries.
> ...

[mdavidsaver (mdavidsaver)]

This is also https://github.com/epics-modules/devlib2/issues/1

[mdavidsaver (mdavidsaver)]

Fix committed. http://bazaar.launchpad.net/~epics-core/epics-base/3.15/revision/12775