[linux-dvb] Re: [RFC][ANNOUNCE] blindscan: auto search everything

[Holger Waechtler <holger@qanu.de>]

Roberto Ragusa wrote:
> Third idea: create our own hw independent ranges and define the
> meaning of the bits (we could use 16 bit, for example).
> Better, let decide that bit 31 means auto-sr and use 16 or 24
> or 30 bits for ranges.That is:
>   if (bit31==0) (bit29-bit0)=symbol rate in baud
>   if (bit31==1) (bit29-bit0)=symbol rate range mask
>   bit30 reserved for future use, must be 0
>
> Yes, I like it.
> We could define the ranges directly or in relation to sr_min and
> sr_max, but with 30 bits I'd avoid this extra complication.
>
> We could have ranges coded this way
>   SR_SEARCH_RANGES      1<<31
>   SR_RESERVED_MUST_BE_0 1<<30
>   SR_RANGE_30M_25M      1<<29
>   SR_RANGE_25M_20M      1<<28
> ...
>   SR_RANGE_6M_5M        1<<12
>   SR_RANGE_5M_4M        1<<11
> ...
>   SR_RANGE_500k_300k    1<<0
> and use (SR_AUTO|SR_30M_25M|SR_6M_5M) in apps.
sounds hard to use. I would prefer the approach similiar to thy Zarlink 
Evalsoftware: pass the frequency and symbol rate ranges to the driver 
and then get interrupted/notified as soon something is found, thenafter 
continue there.

A scan looks like this from the userspace application point of view:

ioctl(PREPARE_SCAN, &setup_range_spec);
ioctl(START_SCAN);

while (1) {
	/* we get notified by poll() */
	wait until status changes and read current parameters;
	select(fe_fd, ...);
	ioctl(fe_fd, FE_GET_STTAUS, &s);
	ioctl(fe_fd, FE_GET_PARAMETERS, &p);

	if (end of range)
		bail out;

	if (channel found)
		store parameters;

	if (weak channel)
		mark channel as weak;

	ioctl(CONTINUE_SCAN);
}

an additional ioctl(CANCEL_SCAN) allows to interrupt running scans and 
to bring back the hardware into a sane state for normal tuning.

discontinous scan ranges should be handled by the application. The 
setup_range_spec struct might look like this for DVB-S scans:

struct dvb_fe_scan_spec {
	unsigned freq_start;
	unsigned freq_end;
	unsigned srate_start;
	unsigned srate_end;
}

A similiar approach works for the mt352 DVB-T demod, there the srate 
fields are not required but bandwidth and the scan_weak_channels bit 
have to be configured. What do you think?

Holger