Use OsmocomBB as OpenBTS / airprobe clock generator

[Harald Welte]

Hi Steve,

On Sun, Apr 11, 2010 at 01:28:27AM +0200, Steve Markgraf wrote:

> >Ideally, we would even use the Calypso-internal PLL (for ARM or DSP) to
> >multiply it up to the required 52 MHz.  However, neither the Openmoko
> >nor the Compal/Motorola phones expose any of the 3 clock output pads :(
> 
> Hmm, 3 output pads? I only see DPLLCLK and CLKOUT_DSP, the third one
> would be CLKX_SPI, but can that one be used for this purpose?

The third one is MCLK, i.e. the clock that the Calypos PLL feeds into
the ARM core.

> I looked at the Motorola W220, which uses the DPLLCLK-pin as TSPACT5
> wired through a buffer to GSM900_TX of the antenna switch.
> 
> see:
> http://www.steve-m.de/projects/osmocom/w220_dpllclk.jpg
> 
> The pin on the buffer is quite well accessible, so we could tie it
> to low (and disable TX with that, but we don't need that anyway,
> right?) and use VC1B as clock output.

Yes, I agree, this should work just fine.  However, using the Altera
internal PLL to multiply from 13 to 52 sounds even better!

> Our code already runs on the W220, but we would need a driver for
> the Si4210 GSM transceiver.

That doesn't sound hard.  Didn't you say that you have documentation?

-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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