[linux-dvb] STB0899 I2C bus bit rate and Skystar HD ?

Manu Abraham abraham.manu at gmail.com
Thu Oct 18 21:51:19 CEST 2007


Konstantin Dimitrov wrote:
> hello All,
> 
> the only place that i can find where I2C bus bit rate is set for the
> budget-ci driver is in:
> 
> http://jusst.de/hg/multiproto/file/096a44e6732a/linux/drivers/media/dvb/ttpci/budget-core.c
> 
> line 506:
> 
> saa7146_i2c_adapter_prepare(dev, &budget->i2c_adap,
> SAA7146_I2C_BUS_BIT_RATE_120);
> 
> with that setting i got 16 locks out of 20 tries on Astra 19.2E, 11538V
> 
> when i change "SAA7146_I2C_BUS_BIT_RATE_120" to
> "SAA7146_I2C_BUS_BIT_RATE_240", i.e. decrease the I2C bus bit rate
> then i got only 3 locks out of 20 tries on the same transponder
> 
> when i change "SAA7146_I2C_BUS_BIT_RATE_120" to
> "SAA7146_I2C_BUS_BIT_RATE_80", i.e. increase the the I2C bus bit rate
> then i got 0 locks out of 20 tries on the same transponder
> 
> as far as i know current I2C ICs can work at any I2C bus bit rate up
> to 400kHz and


The STB0899 can go up till 4MBps! Normally the private repeaters can 
go up till 66 kHz or 100 kHz at a maximum on many demods, but on the 
STB0899, behind the demodulator you have still 400k transfer!


> 
> SAA7146_I2C_BUS_BIT_RATE_80 ~= 400 kHz
> SAA7146_I2C_BUS_BIT_RATE_120 ~= 275 kHz
> SAA7146_I2C_BUS_BIT_RATE_240 ~= 135 kHz
> 
> so why STB0899 can't lock at any of these I2C bus bit rates ?

There are many things to be considered for the STB0899, it is very delicate 
according to STM, even some small things can cause allergy to it. But when 
you have a properly working driver, it shows it's true colours in performance.

When you are racing it to the limits, everything has to be perfect there, not
much of tolerances allowed in such cases.

Manu




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