Dr. Logicprobe (or: How I learned to stop worrying and love the HAMCOP)

Hi all,

Today on IRC, I was discussing JTAG with Spyro, and he suggested that I
used boundary scan on the HAMCOP. I explained that we did not have the
scan order, but his response was simple: "So?" (Well, maybe not stated
just like that.) He then patiently explained to me that I should keep
pumping bits through the boundary scan until I found the magic bit, so
I'll try that.

There's one problem, though.. the output enable bit for the bits that
are inouts. I came up with the following thought:

1) Pump every bit as a 1. Make sure the pin on the flash turns on.
2) Pump half the bits as a 1, half as 0.
2a) If the pin turns on, go to step 1 using the 'half' that we're using
right now.
3) If it doesn't turn on now, then there are two cases remaining: The
enable bit and the out bit are split between the enabled side and the
disabled side, or they are both on the 0 side.
4) Invert the pattern tested in step 2.
4a) If the pin turns on, go to step 1 using the 'half' that we're using
right now.
5) Go one by one through the zeros, setting them to ones. Wait until the
pin turns on.
6) Now go one by one through the ones, setting them to zeros. Wait until
the pin turns off.
7) ???
8) Profit!

Now, the obvious way that this will break is if there is a pull-up on
the pin. In that case, we're sort of screwed and it'll be a bit more
difficult. But in the mean time we will hope.

joshua
Received on Wed Sep 1 17:50:21 2004