A501 memory card detection

[kamiga]

Does anyone know, besides PIN 32 on CNX (aka /EXRAM on Agnus), what checks the A500 performs to consider the A501 online and available for use?

Does the boot sequence include writing a byte/word out to the memory, and then reading it back in? Prior to making it available for use?

I've got pin 32 grounded, and booted off a workbench disk, "avail" still shows only the initial onboard 512k.

Thanks
kamiga

[kamiga]

Detection of Chip RAM and $C0 memory works by (crudely) testing it. The _EXRAM signals Gary to map the $C00000 memory accordingly (ie. generate chip select for Agnus, link busses, etc.).

@ACR: Sent you a PM. I could definitely use one.

@Zac67: Thanks for this. I was thinking, "man, it would be nice to see the actual code for this, and I thought, hrrrmmmm, where would that code is located....right...in kickstart rom" ....and then I remembered this link!

http://wandel.ca/homepage/execdis/exec_disassembly.txt

        ; $C00000 Expansion RAM Checker
        ; -----------------------------

        ; The following routine checks for the presence of memory
        ; in the $C00000 - $DC0000 area.  This is a nontrivial exercise,

Looks like the relevant code is around line number 859.

Very cool.

Thanks guys.
kamiga