Free board offer to OBB developer with a CMU200

Craig Comstock craig at unreasonablefarm.org
Tue Apr 9 03:51:29 UTC 2019


On Sat, Apr 06, 2019 at 09:39:25PM -0800, Mychaela Falconia wrote:
> > So at this point I have some work that others did to transmit a burst on a
> > specific ARFCN.
> 
> What you are describing sounds like a low-level RF test mode,
> transmitting a burst by itself, without any synchronization with a BTS,
> a test mode provided in most GSM modem implementations (FreeCalypso
> has it too) for exercising the RF Tx hardware by itself, without a GSM
> network connection - this test mode is typically used in factory
> production line processes when doing Tx calibration.

It is code which someone else wrote based on I think the available data sheet 
and possibly the sources that you reference (and other versions of similar). I 
have been digging through several of these sources for about a year or so and 
have been working through the existing txburst code. It involves manipulating 
the baseband interfaces that the MCU (mtk6235) provides. There is an immediate 
mode which is used in this case where in a typical case a buffered/programmed 
mode would be used. I don't think it's that far from dealing with the DSP and 
likely is the level needed in order to do a significant part of the work needed 
for layer1.

> > This is a very part-time endeavor for me so I do what I can.
> 
> I am part-time too, I am NOT independently wealthy to where I could
> work on FreeCalypso full-time.  Yet having a limited time budget is
> not an excuse for making poor judgments as to what is realistically
> doable and what isn't, deluding yourself and misleading others into a
> land of false hopes.

I have enjoyed all of the time I have spent on this project and am excited to 
learn as I go. It doesn't feel like wasted time at all. :)

I hope I am clear to those on this list and elsewhere: I'm just working on 
this. I have no idea if or when I will ever complete my goal. You can call it 
slow-ware or something if you like but it isn't exactly vaporware because I am 
making real things work.

> If you really wish to have a shot at working GSM functionality on an
> MTK platform, the only way you might be able to achieve something
> functional would be if you start with MTK's official firmware:
> 
> ftp://ftp.freecalypso.org/pub/GSM/MTK/

Yes. I downloaded that source now just in case it has some missing pieces. I 
already have say 2-5 other source trees available for mostly 62xx chips but 
also 67xx and 68xx chips. Much of the 2G layer1 code is very similar in all 
these source trees.

> You won't have any realistic chance of bringing up any GSM functionality
> on any MTK platform until you get MTK's official fw running on that
> platform in a configuration which you compile yourself from semi-src
> and thoroughly study that MTK official fw and its architecture, just
> like how the people who did OBB on Calypso in 2010 made critical use of
> Openmoko's semi-src as a working reference for the Calypso+Iota+Rita
> chipset.

I may end up doing that if it seems like the right choice. For now I have been 
happy and have made progress without using any semi-src. I have focused on 
gathering "facts" from the source code, data sheets and existing open source 
software.

> Meanwhile, for anyone who needs a working GSM+GPRS modem with full
> source code *right now*, my FreeCalypso offering is the only working
> solution that is available *today*.  In another few years I will
> hopefully also have a self-contained "dumbphone" handset product to
> complement the already-available modem offering, whereas with the
> approach taken by Craig, it is highly unlikely that his approach will
> result in any kind of usable product (be it a phone or a modem) any
> sooner than 2035 at the earliest, and would probably be more like
> year 2050.

Agreed. I can't predict when any stage of my desired end-goal of a usable 
device will occur. I am quite certain I have never mentioned any timeframes 
other than what I would ~like~ to achieve.

> M~

As always I am very grateful for your attention, knowledge and detailed 
responses. They help me immensely in my endeavors.

Be well,
Craig
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