[linux-dvb] Re: Another NAPI question

[Johannes Stezenbach <js@convergence.de>]

Steve Brown wrote:
> 
> What are the plans for the AFC function?
> There seems to be no way to activate this through NAPI.
> Is it planned to remain a user-space function in DVB.cc and leave the
> driver?
> If so, do you plan to pass the afc error term back from the VES (or
> equiv) chip?

The AFC register of the VES chip *currently* can be read like so:
  struct qpskRegister reg;
  reg.chipId = 0x20; /* decoder */
  reg.address = 0x0a; /* vafc */
  ioctl (qpskfrontend, QPSK_READ_REGISTER, &reg);

But unfortunately, my experiments showed that this value is
unreliable and the decoder sometimes loses sync when the frequency
correction is performed. Most of the time the frequency correction
does nothing (e.g. no improvement in S/N or signal strength).

What libdvb does for "AFC" is a trial-and-error scanning of the
frequency range around the desired frequency, until the decoder
reports full sync.

If you have different experiences or more info regarding
AFC, please let us know.

Johannes


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