Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Mon, 28 Aug 2006 09:18:25 -0500

Kate Feng wrote:

Andrew Johnson wrote about mvme6100:
The only sure-fire way around this problem is to check
the Tempe chip's VMEbus Exception Attributes Register after every
write operation and every read that returns an all-1s bit pattern

This can be implemented at the level of the Tsi148 driver
instead of the EPICS driver, right ?

All the EPICS VME drivers that I know assume that they have memory
mapped I/O to the VME card and thus do not make an OS or BSP call to
perform read or write cycles on the VME bus. If they *did* call an OS
or BSP routine then it would be possible for a Tsi148 driver to
intercept all such I/O operations and perform the necessary checks
afterwards. However since they don't (most EPICS drivers create a
struct that directly maps to the board registers and use a pointer to
that struct to calculate the register address) the above requirement
would need major changes to every driver to properly handle the issue of
getting a bus error.
This doesn't mean that the existing drivers won't work; the vast
majority of the time they will be fine. They will not be robust in the
presence of unexpected bus errors though.
- clearly not something conducive to good I/O
performance, and not compatible with any existing EPICS drivers.

At least, only the VME devices implemented with the 2eSST protocols
are eight times faster than the regular one, which somehow compensate
the overhead. The only possible performance gain over the Universe
on the VME backplane lies at the MBLT  via the DMAs of the tempo chip
using the 2eSST protocols, which will be confirmed by Timo.

2eSST is not relevent to the programmed I/O operations I was talking
about above. The issue of bus errors occurring during a DMA transfer
are dealt with using a different mechanism which should be fine on the
Tempe chip.
- Andrew
--
There is considerable overlap between the intelligence
of the smartest bears and the dumbest tourists.
  -- Yosemite National Park Ranger

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System