We have had a bit of a spotty history with getting reliable JTAG bit-
file programming going on our iBOBs using IMPACT and the USB Xilinx
platform cable. Recently the chain seem to have broken completely,
and we wonder if anyone has any hints. Early on we figured out that a
number of our iBOB boards being built with 4.7k pull-ups on TD0
instead of the recommended 200 ohms. We checked all our boards and
corrected this, and things improved dramatically, although we found
from time to time we needed to fiddle with the little adapter board
attached to our platform cable to get the JTAG to restart. We
recently expanded the chain from 4 iBOBs to 6 (i.e. 12 devices in the
chain) and IMPACT basically stopped running. We had built this chain
with longer wire, about 2 feet between boards, to allow for neater
routing. On reverting to the four board chain and our old shorter
cable it stayed broken, we're in a bit of a crunch and could use a tip
here.
Can someone help? Some of our thoughts in the form of questions:
Are there jumper settings on the iBOB we should know about?
Are there any differences on the last board in the chain? The first?
What is the longest wire length allowable between boards?
How many devices in the chain are supported?
We have just one platform cable, trying a second would be good. Could
anyone offer a loan briefly?
Usually TDO goes to TDI as one goes from board to board down the
chain. According to the Xilinx docs, however, when connecting to the
platform adapter, TDI goes to TDI on the first board in the chain, and
the last board has TDO going to TDO on the platform cable to close the
daisy chain. Is this correct?
Any other thoughts or experiences appreciated.
Jonathan & Rurik
