Hi,
since flashing the hh.org bootloader on my swissom cl4 did not
work, we tried to fix this using jtag.
It seems that we have found a subtle way to finally kill the
simpad.
The primary problem, while trying to jtag the pad, was that
the jtag software didn't detect the self soldered cable.
After verifying all soldered connections we figured three possible
sources for our problems:
1. My brother-in-law used higher rated resistors for the jtag
cable, since he had no correct resistors at hand.
2. Basically the mainboard layout could have been altered,
so that jtag would not work anymore, even though the soldering
points are still available. Since jtag is no official feature
and it is usually only used during development, it might
be possible, that the swisscom pads don't support it anymore.
3. Some specific problem with our simpad.
While fumbling around we realised, that the bootloader was starting
even if the jtag cable was connected.
My brother-in-law was a little bit astonished, since he expected, that
the jtag cable should keep the processor permanently in reset state.
Later on he guessed, that it might also be possible, that the jtag
interface only blocks the cpu from interaction with other peripherals.
Somehow I proposed to enforce this reset state by pressing the
reset button while the jtag cable was connected.
We later on guessed that this was the trick to kill the simpad, since
some minutes later we realised, that the cpu started to get really
hot (i.e. hot enough to burn your fingers). Furthermore the
boot messages started to get messed up (i.e. most text was
undecipherable due to strange symbols, just a few strings
remained readable) and finally the simpad didn't boot at all
anymore.
We later on figured, that the strongarm processor provides two
separate reset logics and my brother-in-law remembered, that
he had already damaged another device by triggering two reset
logics simultaneously before.
Since in this other case only a reset IC was killed, we started looking
for such an IC but we have not succeded yet and it might be even
possible, that the reset logic is not driven by an IC but just by an
RC component.
So it looks like we have really bricked the simpad, but we are not
really sure why and furhtermore we still don't know, why the
jtag cable was not detected.
My brother-in-law said, that the resistors for the jtag cable, where
technically unnecessary, but we didn't have the possibility to test
this simplified jtag cable, since we killed the pad before.
The interesting question is wether someone can verify, that the
jtag process works on swisspads.
And ofcourse if we really cannot fix the pad, the question arises
wether it is possible to somehow make use of the simpad screen
as a display. For this we would probably need a controller or at
least some specifications to program a controller, but currently
we have not yet found a model number or any other information
about the display, even the manufacturer is unclear.
So if anybody has informations about the last point, this would be quite
helpfull. On the other hand, if somebody has a simpad with a broken
display we could either buy the mainboard or sell our display.
regards
Sascha
