Progressive Peripherals & Software (PP&S) A2000/040 memory question

[wmaciv]

Is there any data on the importance of refresh rates for this card? I am currently using two chip, 60ns rated 4MB SIMMS, 4K refresh from what I can tell. Is there any speed or stability advantage of going to a 1K / 2K refresh SIMM with this hardware? Nothing in the user manual makes any distinction about refresh rates. I am asking because the PP&S memory autoconfig function only works to configure memory within the Zorro II address range; all other memory is added via an "AddMem" type utility at boot time. This auto config function stops working above about 37 Mhz, but if I boot with the autoconfig disabled, I can easily boot at 40mHz and maybe above. I have an L88M mask 40 MHz rated 040 that runs cool in use at these frequencies. Something in the auto config circuitry or bus does not like the higher clock frequencies at boot time. What is the limiting factor here? Thanks for any help you can provide.

Mac

 

[BLTCON0]

In theory lower-K SIMMs should be preferable.
Say, e.g., a memory chip has 1048576 words (1MxW where W is word width and isn't of particular interest here).
Since addressing is multiplexed in RAM chips and 1048576 = 2^20, the internal organisation of the chip can be:

2^10 rows x 2^10 columns (= 2^20 addresses in total) or
2^11 rows x 2^9 columns (= 2^20 addresses in total) or
2^12 rows x 2^8 columns (=2^20 addresses in total)

The chip markings *will* be different for each case

Now recall refresh is done on a per-row basis.
So with 2^10 = 1024 rows, we have 1K refresh "events"
With 2^11 = 2048 rows, we have 2K refresh "events"
With 2^12 = 4096 rows, we have 4K refresh "events"

The RAM controller still refreshes a row every Z ns, the question now is how high it can count, so you can generally say that using lower-K RAM is preferable.

Obviously you don't get any speed gains, that's determined by the ns rating of the RAM and the CPU's frequency. If the controller e.g. only considers the worst case of 80 ns RAM, you won't get any speed increase using 70 or 60 ns RAM.

If you suspect the card is limited to 2K refresh empty the second RAM bank and see if you get any stability gains - but I doubt this has anything to do with your problem.