I'm having some problems with my gumstix that I'm not sure are related
to the ram refresh rate issues. Maybe someone has some ideas.
Here's the sequence of events that I've followed:
* First I blew up one gumstick. Completely and utterly. I had the
voltages mixed up on the pinout.
* Then I took my waysmall apart and followed the traces to get the
layout correct. I made a small breakout board that had an SMT
pressure connector on it to connect to my little circuit that
contains some MAX 3233 chips on it. I took the stick out of the
waysmall at that stage to use with my new breakout board. That
worked fine. It would talk to both rs232 ports.
* It was time to do some work with the thing, so I put it back into
the waysmall so I could use both serial ports and work via a USB
network connection. At that stage, I started receiving double
echos via the terminal emulator. I figured this was transmit and
receive lines cross on the pressure connector. Jiggling it didn't
stop this and after a little while it wouldn't take any input at
all anymore on the original waysmall.
The stick still worked on my little chassis however.
* Time to upgrade the uboot. First I wanted to simply upgrade the
linux as it seemed less ominous. I was able to flash the linux,
but the waysmall didn't boot. Craig informed me that this was due
to changed environment variables in the eeprom. I changed these
and it booted successfully. However, I only booted it about twice,
then it failed to come up to even a uboot stage. Now, I still
haven't upgraded the uboot yet, so it's conceivable that it is the
ram refresh rate bug kicking in I suppose. I guess it needs this
to be correct to even boot the uboot, surely. It's not using
non-volatile ram as part of the uboot after all right?
* Time to make a jtag cable. I made a circuit based on this one:
and soldered this onto the waysmall's jtag connector. But no go.
Nothing. The ocd commander software stated that the cable was
disconnected. Well, the last time I used the waysmall, I had some
problems with the pressure connector, so maybe this was the cause.
* So I made another chassis computer, with some max3233's for the
rs232 ports, an ldo regulator so make sure that the 74HC244's
would provide 3.3V outputs. Another new pressure connector and a
14 pin connector that would take a ribbon cable connection to the
jtag board (But providing the same signals to the same places as
the 20 pin connections). Still no go.
* I then received a new (Old-style) gumstick. I plugged this into my
own original computer board and I saw it booting linux, so the
stick works. I turned off the power and on again, this time it
only booted to the uboot prompt. Off and on again and nothing. I
never saw it boot again, no matter how much pressure connector
jiggling I did.
* I tried this new gumstix in the waysmall chassis. Also no go.
* At this point I'm thinking that the pressure connectors must get
out of alignment after a certain amount of use or abuse and it's
not possible to see the connections properly on the inside when
the board is in place. So I took the second gumstix that died
during the flash experments and soldered a pressure connector onto
the stix with a hot air rework iron. I then soldered little wires
onto this and connected soldered them onto the similar pressure
connector on my new harness that also contain the jtag connectors.
So right now I'm at a loss. What are the possibilities:
1. Maybe I'm blowing the stixs up with ESD? But I doubt this. I don't
have an ESD clean room. There is some carpet next to me. But I'm
not wearing sneakers (In which case, I would generate ESD) and
I've never actually blown anything up with ESD before.
2. Maybe when the pressure connector jiggles and cross adjacent pins
it damages the stix? I think this one is a definate possibility,
because apart from the stix that died during the flash
experiments, all of the others do experience a little bit of
pressure connector shorting. However, I can't see how it would
cause problems, as the VCC and GND are on opposite sides of the
connection and I don't see the other lines having a problem with
some voltage on them. But maybe they do? A fully charged li-poly
is about 4.2V and one chap earlier stated that the jtag pins on
the xscale chip can take up to 4V inputs. If vcc slipped, it would
also not have any current limiting there either. However, in a
connector slips, vcc would go to rts and gnd would go to nreset.
The rest would be signal shorts. I doubt that that is a problem.
What do you think Gordon?
3. Maybe my stix are not broken but are simply suffering from the ram
refresh rate problem. Because I don't have a genuine mcgraigor
cable I can't eliminate this as a possibility yet. Though I
thought that the circuit that I was using was essentially the same
circuit as Benny is using and he *is* able to talk to his stick.
Because no amount of pressure sensor jiggling can get a new gumstix
working again, I think that they are breaking. I don't want to break any
more if that's the case.
Does anyone have any ideas? Does it appear to others also that my stix
are probably fried, or does the above still leave the possibility of a
jammed, but otherwise still functioning gumstix?
PS. I do have one new module gumstix available here. But I have only two
connectors for them and hence two shots to get them soldered right. I
only have a rework hot air gun to do this with. I think there will be
two problems. The biggest I think is getting the solder paste at exactly
the right thickness to solder correctly. This will be very hard because
the pins are so close together that the chance of two much paste is
quite high. The second problem is simply seeing the correct placing of
the connector before blasting it with air. Once the solder paste is in
place, you can't see the connectors clearly anymore. I'm currently also
making my own boards. I can make tracks down to 0.1mm no problems, and I
do chemically tin place them. But they don't have solder mask on them
nor to I have a solder paste template.
Does anyone have any tips or suggestions of how to get this right first
time or at worst, the second time :) ?