Bunsen
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Wow, that's disappointing You're a bit familiar with AVRs iirc; would a faster AVR help there at all?
I have a few of the CURIO SCSI ICs, but no docs
I have a few of the CURIO SCSI ICs, but no docs
Is there such a thing as a general-purpose bus arbitration IC which can be configured to a specific bus?a bus handler in hardware which isn't a hard to find EOL IC
That would be a pretty magical thing if it existed. I'm sort of picturing a gigantic DIP package with a knob on it marked "SCSI/HIPPI/EPP/ISA/..."Is there such a thing as a general-purpose bus arbitration IC which can be configured to a specific bus?
by: Andrew LynchI have posted another very minor S2I firmware update on the Wiki (0.3B). The main difference is that the ROM automatically starts the SCSI Target Mode Command Processor automatically at boot. You can press to access the Zapple prompt.
Here are some more testing observations:
I pushed the CPU speed to 12MHz successfully. I was unsuccessful at 16MHz. My Z80 is rated for 20MHz. I would guess the limiting component is now the EEPROM which is rated at 150ns. Any thoughts on this? I don't see a faster version of the 28C256 available...
DOS 6.22 FDISK now working!!! It definitively started working when I increased the CPU speed to 12MHz combined with pseudo-DMA. Interestingly, it appears that newer host controllers are MORE tolerant of slower SCSI devices. My older controller (TMC-860) defnitely struggles more as the SCSI2IDE runs slower. Running the SCSI2IDE at 12MHz w/ pseudo-DMA has resolved all remaining compatibility issues I can determine.
The IDE interface is substantially faster than the SD Card interface. I strongly recommend sticking with the IDE interface if possible.
I believe the firmware is definitely ready for serious testing in other environments.
If anyone is building/testing, please keep us posted here!
Thanks,
Thanks Wayne! Wow that is an interesting discovery! Great news on fixing the MSDOS 6.22 anomaly! I imagine the SCSI host firmware might have some timing dependencies built in that are getting tripped up by the slower response of the S2I.
What sort of logic chips are you using on your S2I prototype? If speed has become an issue it is probably time to move from 74LSxxx to 74Fxxx or 74ALSxxx or 74HCTxxx or 74ACTxxx or 74AHCTxxx. Especially the 74LS139 has slow propagation. Typically the 74LSxxx is good up to 20 MHz but when connected as a circuit the propagation delay can add up significantly and break the design. What speeds are your UART, PPI, SRAM, etc? I am a big fan of 74Fxxx but they can be power hogs. Unfortunately the only real ways to find the broken link is to substitute parts or use a logic analyzer to isolate the breakage. Neither is going to be much fun though…
There are some faster ROMs available:
29C256 (Flash drop in replacement) can get as low as 90ns. Probably difficult to source though.
http://www.digikey.com/product-detail/en/AT29C256-90PI/AT29C256-90PI-ND/399193
There are 28C256 as fast as 120ns.
http://www.digikey.com/product-detail/en/CAT28C256LI12/CAT28C256LI12-ND/1631037
Digikey has 27C256 EPROMs as low as 45 and 55 ns but they are UV eraseable EPROM which will be a PITA to use.
http://www.digikey.com/scripts/dksearch/dksus.dll?FV=fff40027%2Cfff80434%2C401985%2C4021d4%2C4022f5&k=27C256&vendor=0&mnonly=0&newproducts=0&ptm=0&fid=0&quantity=0&PV143=30&PV143=16
I am thinking the IDE will be the primary interface for the drive and the SD will act like a big local ROM for modules, disk images, utilities, and other things. It would be nice if it were faster but SD is inherently serial in nature and slow by design. The later SDHC are faster and are nibble wide which helps a lot but we don’t have the spare GPIO pins to drive it. Maybe in S2I V2.
Thanks and have a nice day!
Andrew Lynch