PBI R:Fi - Project Design/Build Log

[TangentAudio]

Here's a schematic of the RAM, MMU and decode logic that I drew up. It was partly an exercise to follow through the logic myself, and also partly to create a nice little one page reference for future use.

 

800xl_ram_mmu_decode.pdf

[Mathy]

Hello TangentAudio

 

As far as I know, Atari used three different MMU's:

 

1) 1200XL/1400XL/1450XLD

2) 600XL/800XL/65XE/130XE/800XE

3) XEGS

 

Sincerely

 

Mathy

 

 

[Joey Z]

My theory above doesn't make much sense now that I've looked at the schematic again after a cup of coffee. Of course /EXTSEL=0 should inhibit /CAS regardless of the state of EXTENB, so it doesn't seem likely U1MB+ or anything else is an issue, and I probably have something screwy on my prototype. What seeing this logic possibly does help confirm is why I have proper functionality in the D800-DFFF window even if I may have a non-functional /EXTSEL on my board. It looks like the EXTENB logic includes D800-DFFF, so it's entirely likely the MMU has actually been the thing inhibiting /CAS for D800-DFFF, all the while masking an issue on my prototype until I started testing outside of that window. I'll go hunting tonight and I bet I will find a dumb wiring error.

If your /EXTSEL pulsing is actually making it to the atari, maybe your timing is wrong. If you don't get /EXTSEL low at the right time, /CAS will go low, and the RAM will output it's data. EXTSEL should probably be combinationally decoded from the address and little else. That's how the Atari decodes EXTENB (which, though internally produced, accomplishes the same thing as you've noticed). Also, keep in mind EXTSEL can only disable the RAM, not OSROM, or BASIC/cartridge ROM, or the I/O region. You can of course disable the math pack, but only with MPD, not EXTSEL....

 

Also, to answer your question about EXTENB, it will go low any time the atari is accessing an address that shouldn't be RAM. This means I/O address (D000-D800), OS ROM if it's enabled (D800-FFFF), BASIC ROM if it's enabled or a cartridge if inserted (8000-9FFF, A000-BFFF), and lastly, self test if it's enabled (5000-5800 IIRC).

[TangentAudio]

If your /EXTSEL pulsing is actually making it to the atari, maybe your timing is wrong.

 

This seems the most likely, since I just pulled it up on the scope and it seems I am only activating it on the latter half of the bus cycle when PHI2=1 ... I'll have to fix the VHDL.

 

[TangentAudio]

Changed /EXTSEL (and /MPD for good measure, even though it seemed fine only being active with PHI2=1) to simple combinatorial logic and it's all good now. My ANTIC/SPI-DMA/Dual Port RAM passthrough test now works without pre-filling the Atari RAM with FF's.

 

Another good catch, it's good to have another set of eyes helping. Thanks!

 

 

[foft]

I've found the freddie data sheet helpful for timing of these signals.

[TangentAudio]

I've found the freddie data sheet helpful for timing of these signals.

 

I've never seen this, can you post it?

[foft]

I've never seen this, can you post it?

http://www.atarimuseum.com/ahs_archives/archives/pdf/computers/8bits/freddie-mcu.pdf

[Mathy]

Hello guys

 

You can of course disable the math pack, but only with MPD, not EXTSEL....

 

That would be a problem in the XEGS, as it does not have MPD.

 

Sincerely

 

Mathy

[TangentAudio]

Hello guys

 

 

That would be a problem in the XEGS, as it does not have MPD.

 

Sincerely

 

Mathy

 

That's OK, I am not initially intending this for XEGS. It's going to start out as an external PBI (and probably ECI) device. I've had some daydreams of rolling in a lot of the functionality of a SIDE2 and a U1MB+ and making an internal upgrade, but that would be down the road.

[Dropcheck]

Progress?

[TangentAudio]

Progress?

 

Bits and pieces. I put some hours in over the weekend doing some boring work towards getting the handshaking working, which is a combination of FPGA work, and code on both the Atari and ESP32. I also put some time in on the schematic, inching that closer to being ready for a PC board layout.

 

As I knew would happen with the arrival of nice weather, I'm spending more of my free time outdoors and haven't been as available to put in long hours down in my lab... but I am hoping to keep the project moving forward over the summer, even if it goes slowly.

[TangentAudio]

Finally, it's actually doing something related to the project title... Just a simple test of everything so far, executing a command/response protocol over the PBI->SPI FPGA link to implement a few of the most rudimentary wifi commands like initializing and scanning. Just a quick demo that shows a scan with just my main two access points visible, then I turn on a test router and re-scan so a third one shows up.

 

 

[Kyle22]

Looking good. Are you considering adding WiFi printing capability?

[TangentAudio]

Looking good. Are you considering adding WiFi printing capability?

 

Printing is something I'd like to do eventually... Not sure when it will happen - still a ton of work to do to make this useful.

[Dropcheck]

How's it coming?

[TangentAudio]

Nothing to report, sadly. Between outdoor adventures and work being busy, it hasn't left much time for Atari stuff.

[Dropcheck]

Nothing to report, sadly. Between outdoor adventures and work being busy, it hasn't left much time for Atari stuff.

 

 

Just checking in to see how things are going.

[Dropcheck]

 

 

Just checking in to see how things are going.

 

Bump.

[TangentAudio]

Outdoor activities have pretty much taken over my attention lately, which is great for the soul but bad for productivity on projects like this. I haven't forgotten about it, though, and still hope to get back to it when my free time and attention span allow!

 

Hope everyone is enjoying their summer as well.

 

-Steve

[HiassofT]

Maybe you should jump on the plane then for a quick trip to Austria. Summer took a break here, currently 12°C and constantly raining. No distractions from outdoor activities and sitting in front of a warm soldering iron is looking like a really good option :-)

 

Weather forcast says we should be back to normal temperatures by the end of the week. Let's hope they are not lying to us!

 

Edit: forgot to add: #winterishere

 

so long,

 

Hias

Edited July 26, 2017 by HiassofT

[w1k]

whats new?

[Dropcheck]

Any new progress on this?

[massiverobot]

This looks amazing. Just reading about this because of the bump... it's the last missing piece for a 1088XEL.

 

And how would this work on a 1088XEL even if I could get the PBI/WIFI today?

[TangentAudio]

Any new progress on this?

 

Sadly, no. I haven't even powered up any of my Atari stuff in well over a year. With so many things competing for my attention these days, it's been perpetually stuck on the back burner. No promises, but maybe I'll be able to get back to it this fall/winter, as that is when I usually get wrapped up in these kind of projects.

 

cheers,

Steve