Re: Apple II DMA for free.

["Bryan Parkoff" <nospam@nospam.com>]

<georg.bieling@gmail.com> wrote in message 
1174756767.117188.109360@l75g2000hse.googlegroups.com">news:1174756767.117188.109360@l75g2000hse.googlegroups.com...
> Hello,
>
> I have tried to write down a way to get a free (in terms of memory
> cycles) and easy to implement DMA channel on the Apple II.
> It has to do with the "6502 trashed memory cycles".
> Would you (more hardware-oriented guys) like to read and comment about
> it ?
>
> <http://homepage.mac.com/jorgechamorro/a2things/a2gratisDMA/
> index.html>

Jorge,

    I am not sure I understand your question.  It looks like what you want 
to reduce wasted 6502 CPU cycles by removing un-needed trash cycles per 6502 
instruction, but it will refresh RAM incorrectly.  You can go to use DMA 
without depending on 6502 CPU.  To do this.  Set high on Phase 1 signal to 
control RAM directly by using DMA.  You may be able to trace how data is 
retreived or stored from / into RAM each ONE cycle out of 1 MHz.  It might 
screw video processor because it uses DMA at phase 1 signal.
    You can try to disable 6502 CPU and use your own secondary CPU according 
to your design to do DMA at phase 0 siginal while video processor runs at 
phase 1 signal.  It might give you the big difference.

Bryan Parkoff