Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Thu, 30 Aug 2001 16:01:48 -0500

We have just tracked down a problem in the EPICS code that drives the
National Instruments NI-1014 board when used with a RISC CPU such as the
PowerPC.  A struct containing a pointer and a short was used to define a
6-byte DMA chaining table entry which is directly accessed in memory by
the DMA hardware.  On RISC CPUs like the PowerPC the size of this
structure is 8 bytes rather than 6 due to CPU alignment rules, thus DMA
chaining on the 1014 card didn't work and the device support would always
timeout.  This problem does not occur with 68K-based CPU cards.

There was also a bug in the driver's check for message length.  The
maximum length of a GPIB message through the NI-1014 driver is 65534
characters, but the code would only reject requests for exactly 65535
characters (check the integer length argument, not the unsigned short
variable it was copied into...).

New versions of the GPIB support that works with PowerPC hardware will be
in the next release of EPICS 3.13.  This support code is unbundled in
EPICS 3.14; the relevent changes will be passed to the maintainer.

- Andrew
-- 
The world is such a cheerful place when viewed from upside-down
It makes a rise of every fall, a smile of every frown

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System