Here is my successful story, I hope this info will be helpful for all Oric fans.
In short I found that Cumulus doesn't make good initial reset pulse to CPU -
the reason can be not enough time holding reset line low or not good TTL level
compatibility or the CPLD output can't discharge the famous capacitor C21.
Or maybe combination of all this possibilities...
Following this steps Cumulus works always on my 2 Atmoses with any of the 6 ULA's:
- connect Cumulus and insert good SD Card, formatted as fat32 with diskimages;
- power-on - don't pay attention to 'zebra' picture on the monitor;
- select any diskimage from Cumulus menu in virtual drive 'A:';
- now the trick - get metal tweezers and connect
shortly pins 1 and 4 of the Cumulus power connector - your Oric should boot!
Interesting side effect: if you connect above pins
shortly for second time - Oric resets in BASIC as there is no Cumulus.
I already soldered simple push button to the connector and everything works fine for me.
After having stable working Cumulus I made some additional tests, here are results and some conclusions:
1.
Power supply - I bought (thanks Chema for advice) an universal PSU 3/5/6/7.5/9/12V and 1.5A.
Cumulus works perfect with 7.5V, 9V and 12V. Additionally I tested with all my other PSU's - everything works again.
Recommended is 7.5V - less heat in 7905.
2.
40 pin cable - I tested with no cable (as on picture in my previous post), with 2x long cables (40pin/80 wires) and
with 3x standard IDE cables - everything works!
Conclusion: type and length of the cables are actually not so critical.
3.
PROM/EPROM - when I replace the standard BASIC PROM with EPROM - nothing works.
4.
Pravetz can be fixed to work with Cumulus too - replace the resistor network RP1 (1kOhm) with 2.2 kOhms,
and C21 (100uF) with 1uF - this makes Pravetz to be an Atmos.
5.
CPLD/PIC firmware - I programed the Xilinx CPLD with the sources from DF svn (of course fixed as
previously discussed) - Cumulus works.
The same is with PIC sources. Conclusion: all sources are OK to be used in future Cumulus batches.
That's all!
.
