MVME-5500 Universe II

[Amit Chauhan <amit@rrcat.gov.in>]

Hi All,

This is regarding the working of Tundra Universe II on VME based MVME-5500 CPU Board.

Three of the important signals on VMEbus are Address Strobe (AS*), Data Strobes (DS0* & DS1*) and Data Acknowledgement (DTACK*).

In a normal VMEbus data transfer cycle, the master asserts AS* and DS* signals. When a slave board responds with DTACK*, the master removes AS* and DS* and in turn slave also removes DTACK* thereby ending the cycle.

Two common types of addressing (for slave boards)are :
A16 (16-bit addressing) and
A24 (24-bit addressing).

On a MVME-5500 CPU,we have observed following three cases:

Case-1:
CPU runs under MOTload (native bootloader) and performs A24 cycle.

1. CPU asserts AS* and DS* signals.
2. Slave board responds with DTACK*
3. CPU removes AS* and DS*
4. In turn slave also removes DTACK* thereby ending the cycle.

Case-2:
CPU runs under vxWorks and performs A16 cycle.

1. CPU asserts AS* and DS* signals.
2. Slave board responds with DTACK*.
3. CPU then removes AS* and DS*
4. In turn slave also removes DTACK* thereby ending the cycle.

Case-3:
CPU runs under vxWorks and performs A24 cycle.

1. CPU asserts AS* and DS* signals.
2. Slave board responds with DTACK*,
3. CPU removes only DS* and not AS*. It expects the slave to remove DTACK*.
4. Only on finding the DTACK* removed by slave, the master removes AS* ending the cycle.
   

Case-3  (A24, vxWorks) is the most used cycle type.
It is causing the problem as not every slave follows the sequence expected.
Some slave boards do not use DS* to derive DTACK*.  They derive DTACK* using AS* only.
In such cases CPU's AS* and Slave's DTACK* remain asserted causing a deadlock.

It seems the vxWorks BSP programs the Tundra Universe II chip for Case-3  in such a way that it behaves differently from Case-1 (MOTLoad) for A24 cycles.

Can we make any changes somewhere in vxWorks BSP or initialization-codes for Universe II so that CPU removes AS* when it finds DTACK* asserted by slave for A24 cycles also, which it is doing for A16 cycles .

Regards,
Amit.