tokalash wrote:Update: There's a C025913-38 inside. So, time to start hunting for a good one, or maybe a more recent STE.
In the meantime, I'll just continue to use it until I see some sign of malfunction (doing frequent backups of the card of course).
exxos wrote:ACK is at 5 volts.. At this time I am not sure if Gigafile or DMA is driving the ACK line, I would assume its the DMA as its at 5volts. Even so , it seems like ACK is not in sync with the data. Sometimes it is, sometimes its close, other times its "out" totally.
Another problem occured with the DMA-chip (see my other post). A long time ago, in this computer the two ROM chips were replaced by six EPROMs with TOS1.4. Later, I added a FPU board. Addition of this Alt-RAM board seems to have been too much on the data bus for the poor DMA chip which obviously does not have enough bus-driving power and started producing data errors (btw. this is the CO25913-38 chip which was reported to produce disk errors in STe computers). I found out that by removing either the new TOS 2.06 EPROMs or any two (out of six) of the old TOS 1.4 EPROMs, the errors disappear.
Further tests showed that the frequency of disk errors was significantly reduced (but not completely eliminated) if I placed a very large (several uF) decoupling capacitor immediately next to DMA chip, and reduced even more if power supply voltage was increased to cca 5.10 V.
Checking the part number of the DMA chip, I found out that it was the CO25913-38, which was reported to produce exactly this type of errors in some STEs (and MegaSTEs?).
My conclusion is that the CO25913-38 version of DMA chip simply does not have enough bus-driving capacity and is thus producing erroneous data on the bus. It seems that it was running near its limits from the start, so that in the original state of my MegaST this made no problems, but since then the data bus in this computer has been loaded more and more with:
- replacing the original two ROM chips with six-chip TOS 1.4;
- adding the FPU;
- adding the TOS 2.06 EPROMs;
- adding the bus transcievers for Alt-RAM;
which, apparently, was just too much for the DMA chip. I suspect that a STe, having a different hardware design than a ST, presents an even higher bus load which he CO25913-38 chip can not handle.
Perhaps putting a buffer between the DMA chip and the CPU data lines might be an alternative fix for the STE DMA issue?
exxos wrote:Thats the thing though, the STE does have DMA buffers.. Its what made me think Atari thought there was bus problems and added the buffers on the STE, but as everyone knows, it didn't work, so Atari produced a updated DMA.
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