N. Coesel schrieb:
At 21:48 08-11-07 +0100, you wrote:
Grant Edwards schrieb:
Can anybody confirm that the JTAG applications work when there
are other devices besides the MSP430 in the TJAG chain?
i can't. ;-)
as i understand, even disabled devices in the change add one cycle delay
when shifting data through the registers of the JTAG. so the JTAG code
talking to the MSP430 would need to know that additional delay when reading.
This is strange. The JTAG specification is very clear on this point. An
unused device should be loaded with a pass-through command which sets the
'delay' to 1 bit.
that's what i meant. the MSP430 also does this on command or fuse check
failure.
but doesn't that say that you need one additional clock when reading a
register? compared to the msp430 alone without the other device in pass
through. so for example reading the msp430 JTAG identification will be
one bit position off when reading 8 bits as usual.
> But there is a problem though... JTAG is often
implemented in a rather stupid way which changes the data and the clock at
the same time. If the clock is loaded heavely by a longer string of
devices, the clock will start to run late causing the chain to fail because
the setup time isn't met any more. Adding an RC delay to the TDI and TMS
sometimes solves these sort of problems.
the msp430 jtag implementations on the PC i looked at do one after the
other. but of course a big enough capacity on one signal still kills the
sync. though the JTAG speeds of the parallel port adapter is usually
moderate. they do not read back the signals, the PC just generates the
clock as fast as possible.
chris
