Use OsmocomBB as OpenBTS / airprobe clock generator

Steve Markgraf steve at steve-m.de
Sat Apr 10 23:28:27 UTC 2010


Hi,

interesting idea...

Harald Welte 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?

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.

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

Regards,
Steve





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