Amit,
I have a document titled "Universe II Manual Addendum" (#
8091142_AD001_05). In section 1.2.7 on page 6 it says:
DTACK* and AS* release
When performing IACK cycles and coupled 8- or 16-bit cycles as a VME
master, the Universe II waited for the VME slave to release DTACK*
before it removes AS*. If the slave card links release of DTACK* to the
release of AS*, a deadlock condition may result because both master and
slave wait for each other to end the cycle. The ANSI VME64 Specification
specifies no slave relationship between DTACK* and AS*, therefore no
assumptions on its behavior should be made by the
slave.
The Universe IIB/IID does not wait for DTACK* to be negated before
negating AS*.
The conditions for this behaviour seem to be quite specific in
several parameters which could vary between your cases. Could case 3
differ from cases 1 and 2 in being an interrupt cycle, for example?
> 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.
>
Regards,
Andy
P.S. I don't know where I got my copy of the addendum from but you can
search online for "8091142_AD001_05".
IDT bought out Tundra Semiconductor and keep some of the
documentation behind a registration wall. Even after I gave their
marketing department my details I couldn't find documents describing old
versions of the chip on their website, they only document the stuff
they're currently selling :-(
P.P.S. This email probably won't thread properly with the originals,
apologies.
--
Andy Cousins
[email protected]
01235 778050
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