🚀 go-pugleaf

izumi@pinoko.berkeley.edu (Izumi Ohzawa) writes:

>In article <1992Aug26.060638.10407@ee.ubc.ca>
>  williamb@ee.ubc.ca (william burchill) writes:
>>A floating bus is not going to confuse a memory testing program, that's
>>what it's looking for.  What do you mean "didn't work well"?

>Well, at the risk of making myself look totally stupid, the following is a
>simplified version of what I am trying to do.  I do use other test patterns
>in addition to $5a5a5a.  Failure on any one pattern should break the loop.
>The program just doesn't exit the loop.  I have never written a memory
>test program, so please forgive some ignorance :-)  Thanks.

>---------------------------------------------------------------------

>ERAM_Base	equ	8192		; Start address of external DSP RAM on NeXT
>	
>	<some init stuff>

>	move	#>ERAM_Base,R0
>TestLoop
>	move	#>$5a5a5a,b		;load test pattern
>	move	b,x:(R0)		;write to a memory loc
>	move	x:(R0)+,a		;read back into A1, post-incr address.
>	cmp	a,b
>	jne	memory_fail

>	<same things with different test patterns>

>	jmp	TestLoop

>memory_fail
>	<report R0 value to host>


>--
>Izumi Ohzawa
>USMail: University of California, 360 Minor Hall, Berkeley, CA 94720
>Telephone: (510) 642-6440     Fax:  (510) 642-3323
>Internet: izumi@pinoko.berkeley.edu (NeXT Mail OK)

A better test would be to load different values in a number of locations,
then go back and verify all the locations. The idea is to seperate the
write and read operations so a floating bus doesn't "remember" the
value. And don't use the address as the data on any processor with
multiplexed address-data lines because this can also cause problems.

A good test is to use a psudo-random number generator to write all
locations, then read and verify all locations. Repeat with the inverse
of the data from the first pass. This will catch stuck bits in memory,
and address lines open or shorted.


-- 
------------------------------------------------------------------------------
Robert Wiegand - Motorola Inc.
uunet!motcid!wiegand
Disclamer: I didn't do it - I was somewhere else at the time.