On 10/05/11 18:57, Michel JAOUEN wrote:
Hello,
For supporting optimized jtag chain length, you should look at CJTAG
specification, with star topology support.
CJTAG is not yet supported by openocd.
Best regards
Hello Michel,
I had a look at the 1149.7 standard which seemed very promising at first.
However, a couple of issues give me the impression that 1149.1 is the
safest approach :
1- No support in OpenOCD. I guess this should't be too much of an issue
since only the JTAG driver would need to be rewritten. The ZBS is
already implemented (simply a special "pathmove" sequence). Therefore,
only the escape sequences where TMS is used as a clock while holding TCK
at '1' really needs to be added.
2- JTAG adapter lack of support for 1149.7 features. I currently have a
JLink adapter, and I'm afraid the 'TMS as clock' feature is not handled
as efficiently as a normal TDI/TMS scan (a separate command is necessary
to change the value of TMS, whereas a scan operation can be performed in
bulk). However, I don't know how much of a performance hit I should
expect from this...
Can you comment on this ?
Do you know if other adapters would handle this better ?
Do you think those issues justify sticking with 1149.1 or am I being too
conservative ?
Kind regards,
Sébastien.
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