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Re: CB030, A 68030 SBC for hobbyists [message #6944 is a reply to message #6941] Mon, 20 January 2020 20:39 Go to previous messageGo to previous message
plasmo is currently offline  plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA
Senior Member
Alan,
The BDOS/CCP for CB030 already has the 68010 patch as described here:
https://www.retrobrewcomputers.org/doku.php?id=builderpages: rvumbaca:start
I do enable the instruction cache in the monitor before starting up CP/M68K. The curious thing about the privilege violation is it is flagged when cache is enabled going into CP/M68K, but if I disabled the cache before starting up CP/M, the CP/M program would run just fine. The instruction that's flagged with privilege violation is "move.w ccr,d0", but that is actually not a privileged instruction.

To accommodate 68010, the exception handler supooses to "dynamically change the "move from SR" instruction to the non-privileged "move from CCR" instruction. I need to investigate how that's done, perhaps it is a self modifying instruction that need to flush the cache first...

Thanks for the heads up about 32-bit I/O write that may actually be cache regardless of the CIIN pin. Must be one of those race conditions involving write back of data when the data is also immediately read back. I do use CIIN signal to disable I/O caching, but all my I/O ports are 8-bit wide, so I shouldn't have that problem.

I do plan to turn on 030's synchronous termination along with burst mode filling feature. I'm interested to see what kind of performance improvement possible with that.
Bill
 
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