Test and verify Autoconfig working with sidecar port expansions (e.g. A590) and implement DMA bus-arbitration.

[jbilander]

Test and verify Autoconfig working with sidecar port expansions (e.g. A590).
/CFGIN is GND on the 86-pin expansion edge hence anything plugged in there will Autoconfig directly with no delay. In other words: Risk for bus-contention if the SF500 and for example an A590 Autoconfigs at the same time. However, /CFGOUT from that device should work and make it possible to connect a wire to /CFGIN of the SF500 in a daisy-chain manner (like in a A2000 zorro backplane). Need to experiment with this if/when I get my hands on an A590 or GVP.

Please don't fiddle with this unless you know what you are doing. Meaning don't plug anything into the side expansion of the A500 mobo with the SF500 installed unless you know what you are doing. Bus-contention might damage your hardware.

TODO:
Implement bus-arbitration and test sidecar expansions such as A590 and GVP HD+ to allow for DMA to the SF500 fast RAM.
https://github.com/jbilander/SF500/blob/main/ISE/SF500/rtl/main_top.v#L61

[jbilander]

I have now implemented this and it looks like everything is playing nicely with an A590.

8cf910a

The A590 can for example be set to Amnesia (jumper setting on A590 PCB) and boot from its hard drive and DMA into the Fast RAM of the SF500.

For Autoconfig to work a jumper wire has to be connected/soldered from the CFGOUT on the expansion edge to the CFGIN on the SF500, like this:

I will leave this ticket open until other sidecar expansions such as a GVP HD8+ has been tested and confirmed working as well.