N. Coesel schrieb:
At 23:12 08-11-07 +0100, you wrote:
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.
Actually, you'll need to compensate for the number of devices in that chain
to position the data correctly.
yep
> It has been a while since I wrote a jtag
implementation, but the first thing my routine did was probing the number
of devices in the chain in order to determine the amount of padding bits
required to get the right data in and out of a device.
using the known value for the JTAG ID of the MSP430 this should be quite
easy. as Grant has the necessity he might be willing to add such a
detection to libMSP430mspgcc? ;-)
jtag/msp430/JTAGfunc.c::GetDevice() might be a good place to do that
(around line 155 adding a loop, maybe).
and adding an option in jtag/msp430/MSP430mspgcc.c::MSP430_Configure
to enable automatic detection or force a certain value? i'd probably
leave the the default to "force 0 clocks" (just to not break any
existing systems) and "-1" for auto detection which must then be enabled
by the user with a call to MSP430_Configure
maybe there is also the possibility to set all devices incl MSP430 into
pass-trough and just count the delay of a simple pattern shifted trough.
and i don't know how to ensure that the seconds device is in pass-trough
mode, which would be good if it were when testing the MSP430 ID.
chris
