Experimental Physics and Industrial Control System
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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.
- CPU asserts AS* and DS*
signals.
- Slave board responds with
DTACK*
- CPU removes AS* and DS*
- In turn slave also
removes DTACK* thereby ending the cycle.
Case-2:
CPU runs under vxWorks and performs A16 cycle.
- CPU asserts AS* and DS* signals.
- Slave board responds with DTACK*.
- CPU then removes AS* and DS*
- In turn slave also removes DTACK* thereby
ending the cycle.
Case-3:
CPU runs under vxWorks and performs A24
cycle.
- CPU asserts AS* and
DS* signals.
- Slave board
responds with DTACK*,
- CPU removes only
DS* and not AS*. It expects the slave to
remove DTACK*.
- 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.
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ANJ, 16 Dec 2015 |
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