sysBusTas problem

[rab@csg.lbl.gov (Robert Belshe)]

 I am debugging an application which has two VME crates 
 connected by a Bit3 413-1 bus coupler.   This coupler 
 allows processors in each VME crate to transparently access 
 memory which is in the other crate, and also has 2MB of 
 on-board memory which can be accessed by either crate.
 
 We use EPICS 3.11.1 and vxWorks 5.1, the processors are Motorola
 MVME166s and MVME167s.

 I am using sysBusTas() to test semaphores in each memory
 which are used to prevent access conflicts across the Bit3
 coupler.  This is necessary because the Bit3 is essentially
 a half-duplex device.

 The problem is that, occasionally, one of the tasks will get a
 bus error accessing the memory on the Bit3 coupler, and at the
 same time, another task will hang in  _vxTas, trying
 to access the semaphore in the other VME crate.  _vxTas 
 is the kernel routine called by sysBusTas.  The Bit3
 documentation states that RMW instructions between the
 two VME busses are supported.

 If anyone else has experienced test-and-set problems,
 with Motorola cpus or problems with the Bit3 bus coupler, 
 I would appreciate your suggestions.

 Thanks,  
 Bob Belshe
 Gammasphere Data Acquisition