Having checked the datasheet in more detail, you're quite right, it does appear to be out of spec, especially as the voltage coming out is actually slightly higher than the 1.3V required in the design.
Likewise, I can't see how 1.3V instead of 1.2V on Vccint is going to stop the IO at the DAC side from working, when everything else seems fine.
Likewise, I can't see how 1.3V instead of 1.2V on Vccint is going to stop the IO at the DAC side from working, when everything else seems fine.Once you're out of spec, you're in terra incognita, and anything can happen. For all we know, FPGA might be now half brain-dead and outputting a mains voltage on its pins just for the hell of it.
1.2v is fine for your design. The overclock is way too small to need any boosting. I mentioned it as a last result.
The way I designed the core, errors from overclocking would only represent glitches in the core memory, however, since you confirmed that the Z80 reads and writes to the core memory with the RS232 Debugger, this isn't where your problem lies.
(Only the core dualport ram is running at 250MHz (Of the 240MHz limit reported by Quartus) with an AB-mux switch. And only around 8 signals are out of slack by less than 0.1ns. Everything else runs at 125MHz and report all in the green by a good margin.)
Did you check that the syncs are coming out of the right pins of the VGA connector?
Are you sending +5V to pin 9 on the VGA connector so that the monitor +Vsense pin knows it is being connected to a turned on video card?Never mind, your old development board doesn't have it.
Also, pins 5,6,7,8 and 10 should be grounded.
Did your scope show a proper HS and VS coming out of the VGA connector, when connected to a monitor? This should at least turn on the monitor.
What was the frequency of the CLK output to the DAC?
Can I have a copy of your latest Quartus project? Your GitHub has only single files and I will not download all the files individually 1 by one.
Not read the 40 pages preceding this - but it might be an idea to make the simplest 'hello world' code and start testing the basics and work up from there. Sounds like you need to establish what is working and what is not at a basic level.
I would still 'drag' solder all the pins on the sides I mentioned.
In fact, with normal leaded solder, I would blob solder the pins, then, using solder wick, wick us the excess.
You have nothing to loose at this point.
I'm waiting on some PS2 keyboard connectors - when they arrive, I can start on working on keyboard integration into the project. That'll make my computer fully stand-alone, so it's a major milestone for me. After that/while I'm waiting on the post, I'm starting to look into integrating an AY-3-8910 or YM2149 (old 80's sound chips) into the FPGA, somehow. I have spare IO to drive a stereo output, it's just a case of adapting what little I can find out there to work on my EP4CE10. I'm also giving some thought to how I'm going to give the Z80 access to an SD card via the FPGA too.
Congratulations!
If you have documentation describing how it works, I would just implement it inside FPGA too
(sound chips of that era were very simple - just a bunch of various waveform generators and a mixer to mix them together), and add an I2S DAC to actually output sound. This will also open a possibility of outputting high-quality audio too (like waveform players, which present in some audio chips of that era or maybe a bit more recent), as all I2S DACs support at least 44.1 kHz/16bit format (this used to be called "CD quality" as that's the format used on audio CDs, of course they support lower bitrates too). I2S bus is also extremely pin-efficient, requiring only 3 pins (bit clock, left/right signal and a serial data line), and it doesn't require particularly high frequencies too (unless you want to output audiophool-grade signals at insane bitrates, even though most people would never hear the difference).
Also - have you considered placing it all on a single PCB once you ensure your prototype works?
I'm definitely no audiophool - in fact I'm pretty much tone deaf. Whilst the idea of CD-quality output is nice, it's not essential - I'm working with an 8-bit processor and am looking to recreate audio capabilities of its era, generally (though any improvement would be great; I'm obviously not too concerned about being period-accurate, otherwise I wouldn't be using an FPGA in the first place!)
It'd be an expensive PCB and besides, I've made it to be as modular as possible. What you see in the previous post is a stack of five cards, from bottom to top:
Congratulations!
Too bad that over a few months gone to waste on an inverted reset input signal.
At least the RS232 debugger wasn't tied into a reset and still functioned, otherwise with nothing working at all, who knows what you would have done with what would have been almost a totally dead FPGA...
Come of think of it, I also wonder when (historically) DMA became a thing in computers, because playing waveforms off storage it real time is going to consume quite a bit of CPU time. My memory is rather fuzzy on that I was born in 84, so most of pre-IBM PC stuff went before I got into computers
I just think that having a single board (or more sensible modularity a-la computer motherboard with main board and extensions as opposed to "sandwitch-style") looks better, but it may be just me
Oh, and of course continue working on the software side for the video output. I'm tempted to start investigating the graphics modes on the FPGA/MAGGIEs and develop some graphics functions (PLOT, LINE, CIRCLE etc) in software - but I'm wondering if they could be done in hardware somehow, too?