Re: ZIP Chip Heartbreak

[gtolar@blkbox.com (Glynne Tolar)]

Todd P. Whitesel (toddpw@frappe.ugcs.caltech.edu) wrote:
: gtolar@blkbox.com (Glynne Tolar) writes:

: >supported by all //e accelerators) couldn't the CPU when it detects a DMA 
: >signal (that I know makes it to the CPU!) just flush its cache?  I know 
: >you'ld have some speed loss.  Just a thought.

: If you could get the DMA signal to the CPU, sure.

: However the Zip8 would need a test clip for that, and that's more trouble
: during installation than many customers want to deal with.

: On the 8 bit Apple CPU socket, the only way to detect DMA is to watch for
: a suspiciously long delay in the main input clock, and this is not easy
: to do reliably without some tricky analog circuitry. I think Zip did the
: right thing to not tackle it.

Now I don't have the 6502 pinout in front of me but I seem to remember a 
DMA signal line to the CPU.  Otherwise how would the CPU know to stop 
when a DMA cycle is occourring?