[Coco] More sneak peeks

RETRO Innovations go4retro at go4retro.com
Wed Jul 20 13:10:46 EDT 2016

On 7/20/2016 6:22 AM, Brett Gordon wrote:
> I finally read the cs8900 data sheet.
Stay awake now...
> Is there still the option of mapping
> in packet ram?
All of it flows through the CPLD, so it's possible, but I had actually 
planned on mapping it via IO as 16 locations in $ff40-$ff7f (any 
suggestions on where to sit it?) as that was easiest and most compact.
> I must admit that the Fuzix implications of mapping out
> 0xc000 scares me a bit...but I think there's a way to handle that - not
> sure it's worth it just for interrupts.  I can't picture the outb inb
> interface being horribly slower than mapped memory.
I had a similar concern.  Mapping it into external ROM space means that 
external ROM apps will have to copy themselves (a portion anyway) to 
RAM, and bank out the ROM so they can reach the memory mapped RAM on the 
cs8900.  That seemed a high bar to set.

So, for now, assume it's IO mapped.  Let me know the spot you'd prefer 
it sit, and I'll write the Verilog and test and send to you.


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