[Gta04-owner] GTA04A5: you will hate and you will love this mail

H. Nikolaus Schaller hns at goldelico.com
Wed Feb 10 20:27:44 CET 2016


Hi all,
you might wonder what the status of the GTA04A5 is.

Unfortunately there has not been much progress since I had to spend much
more time on making the Pyra (OMAP5) hardware working and verifying that
it is indeed mass production ready than anticipated. This was really exhausting
because it was squeezing a phase that would normally need several months
into just some weeks.

There had been a lot of details to be fixed. Not much if you see the result,
but each issue needed 110% attention for several days until a reliable
fix was found (and some are still open). For example, there were boot problems,
where the Linux did sometimes start to boot, but suddenly stopped. Sometimes
it reported CRC errors.

This turned out to be a 15pF capacitor to attenuate the MMC
clock signal since it may disturb the GPS receiver (63th harmonic of the
25 MHz clock). A lesson we learned twice for the GTA02 and GTA04.

But this time the 15pF was good for GPS but too much for the MMC.
It made the MMC interface of the OMAP5 to fail spuriously. Such bugs
make grey hair and need a lot of time - and can't be parallelised by
having more people to work on it.

But now, we are almost through and the OMAP5 is starting to work reliably.

This has a nice side-effect, which is very important for the GTA04A5 project
and the reason why I report it today.

The GTA04A5 needs some replacement components because the old
ones used in the GTA04A3 and A4 are no longer available. Even for
money.

One of them is the WLAN/BT combo W2CBW003.

So the plan is to replace it by a modern WL1835 module [1] which adds
more WLAN frequencies, speed and adds Bluetooth BLE 4.0.

But it would be risky to throw it into the schematics, make a PCB
layout and build the ~100 GTA04A5 we have on plan. The risk is
that it does not work and we have no chance and money to fix.

Fortunately, the Pyra also has such a module :) And yesterday, I was
able to get it alive for WLAN and today for Bluetooth. This means that
the way it is wired up to the OMAP5 MMC4 interface and UART2 is working!

And, the way the setup is done in the Device Tree also works.

Since the OMAP3 is not different for these interfaces, I am now sure
that we will not make a mistake if we throw in the WL1835 into the
GTA04A5. This is the good thing! It simply will work with the 4.5-rc3
kernel (and slightly different commands in user space).

The other decision blocking the GTA04A5 production is the 1GB RAM/NAND chip.
Before deciding to solder them all on the ~100 GTA04A5 boards, I would

like to test it a little with some old (partially broken) GTA04 board. This means
desoldering the original 512 MB PoP (Package on Package) RAM/NAND
chip. But without damaging the DM3730 CPU. And then solder the different
PoP chip on top [2].

Desoldering is easy (since we now have a new vapour phase machine
with BGA desoldering tools). But soldering a new chip, especially
Package on Package is really tricky. First experiments did make the
new chip swim away so that it was soldered in a wrong position :(

Therefore we have aborted that to find a solution. There are ideas,
but this needs more experimentation time (i.e. days) until it becomes
successful. Unfortunately another topic queued up behind making
the Pyra handheld production ready.

So I have to apologize that we can't keep the availability date, but
it is really not much missing. Except time to do what is needed.

I am really sorry for that delay which might come a little unexpected
since I did not even give some status updates in the last weeks.
This is something I promise to change again.

There is also something on the horizon: a Kernel and QtMoko hacking
weekend. The plan is to meet in some cosy place and have some core
hackers just work in two teams to fix remaining kernel issues on one
side and overhaul QtMoko to run on top of stock Debian Jessie. Replicant
will also be represented, and we hope that we can then even use our Letux
standard kernel for Replicant.

Please let me know if you want to participate/contribute.

And of course if you have questions about the GTA04A5.

A final note: we have a new mailing list for Letux kernel development [3]
so that this list does no longer need to be cluttered by tiny details and patch
discussions.

Sorry again for the delay and thanks for your patience.

-- Nikolaus

[1]: http://www.ti.com/product/WL1835MOD
[2]: https://en.wikipedia.org/wiki/Package_on_package
just a note: we have the "or less" variant in the picture: 0.5mm on top and 0.4mm on bottom
[3]: http://lists.openphoenux.org/mailman/listinfo.cgi/letux-kernel



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