FPGAARCADE minimig compatible board, comments?

[freqmax]

It might be useful to have a 68020 + 68841-MMU. When your at it anyway..
A single 68030 does the same job too.

Do you have any idea on the peak di/dt of the FPGA?, it has relevance on the latancy response of the buck converter especially for the 1,2V rail.

I see you use 2,5V with linear regulator for the VTT to DDR memory. I been pondering if one can drive this with an buck converter aswell, or if the noise problems would be too great.

Guess the Minimigs get an incentive to go dynamic ram now that the fpgaarcade-replay board has 32 MB, and the Minimig has 2 MB

(your board name is FpgaArcade-Replay v0.0 ?)

[mikej]

I expect the DDR terminator and all the resistors can be not fitted on the production board to save cost. I'll see what it does to the memory timing window.

The board will be v1.0 when it is released to production.

I have a 68030 on my desk but it is a huge PGA version.... The 68020 is needed to get the A1200 core up and running.
/Mike

[yssing]

Did I miss something?? Is AGA supportet?
Sorry for the dumb question.

[tonyyeb]

AGA not supported yet but I would think it is only a matter of time, especially as WinUAE has good AGA support already.

[freqmax]

Here's an Amiga graphics roadmap:
1985 OCS  (A1000, A2000, A500)
19~~ Ranger
1990 ECS  (A3000, A500+, A600, A2000)
1992 AGA  (A1200, A4000, CD32)
1993 AAA  -  
1993 Hombre -

It should be possible to implement them all given enough hackertime

So you could select to have an A500 with AAA and SID sound.. or whatever mutation gone wrong test you want that day :-D

Ofcourse there's also the options of Picasso, or some selfdesigne graphics subsystem.

Edit: ECS/A2000

[Darrin]

You missed the later A2000 off the ECS machines.

[jkonstan]

freqmax,

DDR VTT (1.25V) termination regulator can be linear or a buck switching regulator that was especially designed for DDR termination use.

 :-)

[freqmax]

Ie you can't use an ordinary buck converter for DDR VTT ?

[jkonstan]

Ordinary buck regulators are not really designed for DDR VTT use. You may find a few that can meet the specs to be a supply for DDR VTT and for VREF on DDR. However, semiconductor companies make special regulators for VTT termination & VREF.

[freqmax]

What are the special VTT requirements?

As a sidenote, buck regulated power won't do for A/D either?

[jkonstan]

-Ultra-fast transient response

-VTT must sink and source current

-Low (switching noise for buck) noise on VTT

-etc ...

[jkonstan]

Check out this NSC app note for Linear VTT regulator.

http://www.national.com/an/AN/AN-1254.pdf

[freqmax]

Reminds me of the nasty situation where pull-up to higher voltage supply may cause lower supply rails to have higher than designed for level.
I recall Xilinx had some app-note on how to solve it. But one might be a resistor and zener in series that just burns it away (hopefully ).

(I think it's related to the exploit that uses the builtin protection diodes to attach a 3,3V pullup to get an 3,3V-TTL compatible i/o)

[mikej]

yes, this is what R86 is doing on the 2V5 rail - providing some load. Some of the configuration pins are 2V5, current limited with a resistor but driven from a 3V3 source. You get some leakage through the IO cell protection diodes which try and raise the 2V5 supply. Most DC-DC converters can only source, not sync current (that's why I use a linear for VTT) so your 2V5 gets driven upwards...

/Mike

[AJCopland]

@freqmax, jkonstan, mikej:
Wow, now I know how my girlfriend feels when I'm talking about programming! :-D

Andy

[tonyyeb]

@ AJC

Lol! A moment of self realisation has just hit me!