RAM access via JTAG may interfere with CPU

[GoogleCodeExporter]

Currently when SRAM is accessed by JTAG, CPU may receive completely wrong
data thus crashing the program. Bus hold should be used to suspend the CPU
during JTAG access.

Original issue reported on code.google.com by svof...@gmail.com on 17 Dec 2007 at 8:39

[GoogleCodeExporter]

USB API is evil.

So far I could make it set HOLD signal upon iRxD_Ready, this way it manages to 
get
HLDA before actual RAM request needs completion. There's no flow control of any 
sort
so it's hard to interfere.. It works now, transparently, but it's far from 
being elegant.

Probably, it is possible to improve on it. In CMD_Decode, if oHOLD is set upon
RxD_Ready, iHLDA sets in time. The only problem, it seems, is that there are
different sorts of commands coming from Control Panel and they seem to lock this
simplistic circuit. 

Original comment by svof...@gmail.com on 19 Dec 2007 at 1:38

• Changed state: Started

[GoogleCodeExporter]

Setting hold upon iRxD_Ready chronically doesn't work.. Having really no desire 
to
struggle with mostly a PC-side software issue (poorly written "Control Panel" 
demo),
this should pass for a fix.

 * Read/write of SRAM via USB API Control Panel works flawlessly.
 * Just for a case, manual bus hold switch added: SW7

Original comment by svof...@gmail.com on 19 Dec 2007 at 8:18

• Changed state: Verified