exxos's Atari, Amiga & retro forum

ijor wrote: 16 Aug 2024 18:41

Badwolf wrote: 16 Aug 2024 10:39 It seems that the blitter drives the data quite early during a write and doesn't hold it very long.

Hi Dave,

As I said in my previous message, I'm not sure that is the problem. Unless you changed the code, it seems the problem is the opposite, your SDRAM controller is too fast.

As I mentioned in my previous message, your "ACTIVE" logic at the DRAM controller is level triggered. And since you are too fast for Blitter, you start a second SDRAM write access. I performed a quick simulation. This is the simulation waveform:

Oh gosh! Sorry I overlooked that in the general confusion of losing my code.

I have changed the code (I found the old code -- hurrah! -- I simply don't know how to use git properly). But I think I was seeing the same problem and the active signal remains level driven.

The current code is here -> https://github.com/dh219/DSTB/tree/altramwork2

At one point in the codebase it was impossible to get back to STATE_IDLE until DS were deasserted, so I thought ACTIVE was safe, but I see I've tried to shortcut things in an effort to speed the process up that I've allowed it to return to IDLE early on a write now -- your theory certainly fits!

I did find another similar bug recently where it was going around the cycle twice, but that was an error in the DTACK logic at the time.

I'll give it another look.

Many thanks for the analysis!

BW

@ijor, I'm such a fool.

That appears to be exactly what it was and I completely looked past your comment previously.

I can't believe how many days I've spent on that. Including writing test programs and adapting blitfix. :oops:

What a plonker.

Obviously I can't be sure it's 100% stable yet, but I'll give it a bit of a hammer now.

Thanks again Ijor.

:dizzy:

BW

https://github.com/dh219/DSTB/commit/7b ... 263027d0f1

Badwolf wrote: 16 Aug 2024 21:54 That appears to be exactly what it was and I completely looked past your comment previously.

I'm just glad we (apparently) found the problem.

@ijor, I'm such a fool.

Only smart people say that, really.