[linux-dvb] Re: [Patch] Adding support for the Hauppage HVR1100

Johannes Stezenbach js at linuxtv.org
Tue Nov 29 02:42:41 CET 2005

On Mon, Nov 28, 2005, Steve Toth wrote:
> I did discover an issue with the I2C gate on the cx22702. I raised this 
> last week. Basically, the cx22702 module expects the gate to be closed 
> (blocking access to the pll from other modules). Now, by default, I 
> start the part in 'open' mode then the board specific configs (during 
> _init)  determine whether the gate is acting in open or closed mode.
> The default behavior for existing drivers has not changed... The gate 
> will be closed at all times.
> For the HVR1100, we leave the gate OPEN at all times... This approach 
> felt like a good compromise.

Hm, many digital demodulator data sheets say the i2c gate's
purpose is to isolate the PLL from the demods i2c bus
to decrease phase noise (i.e. signals on the i2c bus
may decrease signal quality due to interference). Thus the i2c
gate should be closed except when talking to the PLL.

On some parts (IIRC stv0299) it even is implemented in such
a way that a STOP condition on the I2C bus automatically
closes the I2C gate.


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