Re: more cx24123

[Manu Abraham <abraham.manu@xxxxxxxxx>]

Yeasah Pell wrote:
> A few more cx24123 patches:
>
> cx24123-sdthresh.patch simply sets the soft decision threshold properly 
> for the specified FEC rate. For the DVB standard, it's very simple -- 
> it's only different for the 1/2 FEC rate. However, the spec recommends 
> this, so it should be done.
>
> cx24123-errcnt.patch changes the bit error counter configuration to be 
> actual BER (previously it was returning a ucblocks value for both 
> ucblocks and BER), and eliminates ucblocks entirely (it isn't practical 
> to get both values with this demod, and IMO BER is more important)
>
> It also replaces the BER-threshold-based SNR estimation with something 
> based on the demod's Es/No counter. It's still totally bogus, since the 
> card only gives Es/No in a raw count (of symbols observed below a 
> certain amplitude threshold) and it's not clear to me exactly how to 
> convert that into a meaningful Es/No so that it could be ultimately 
> turned into a proper SNR dB figure. But it's still better than the 
> BER-based figure, for a couple of reasons: the BER window is large 
> enough that it doesn't update very frequently (especially for lower 
> symbol rates), and you need a signal lock to get any BER data whereas 
> the Es/No does not (so you get data even when there's no signal lock) -- 
> in practical tests, the count ranges from around 32k for me with little 
> or no signal, to a very strong signal giving nearly full scale 64k. I'm 
> sure additional math can be done on this value to improve its 
> meaningfulness, but it's at least the right raw quantity to base SNR on 
> and it's much more useful even in this bogus form.
>
> cx24123-hwalgo.patch changes this card to use HW algo tuning. This has 
> been one of the driver's main problems from the beginning, and as a user 
> I've always partially gotten around the issue by changing the module 
> parameter that lets you alter swzigzag speed to some absurdly high 
> value. This demod has a very robust acquistion and carrier tracking loop 
> built into it -- you can set the acquisition and lock band to be 
> anywhere from fsamplerate/8 all the way up to 10MHz, and it tracks 
> relatively quickly. The problem is that some types of signals (low 
> symbol rates especially) can take a few hundred milliseconds to tune 
> under some circumstances, and with the software zigzag or retuning on, 
> it prevents the demod's state machine from ever reaching the tuned state 
> -- every time it does a retune it resets the whole search back to zero, 
> so it ends up searching just part of the acquisiton space over and over 
> again and never acquiring lock. (I think the AGC may be reset by a 
> retune too, which if that's true is probably most of the problem right 
> there)
>
> Given that the demod itself already has a state machine that seems to be 
> at least as good as what the swzigzag and other dvb_frontend retuning 
> does, and they conflict in ways that sometimes prevent or delay tuning, 
> I think the best thing right now is to disable SW tuning for this card. 
> It improves performance dramatically for me anyway (especially with low 
> symbol rates)
>
> Comments and/or testing welcome.

Sounds cool, i will test it out on the box that i specifically got up 
for testing DVB stuff.


Manu


> -y
>
>
> ------------------------------------------------------------------------
>
> diff -r 265f2c767b45 linux/drivers/media/dvb/frontends/cx24123.c
> --- a/linux/drivers/media/dvb/frontends/cx24123.c	Mon Jul 24 15:19:37 2006 -0300
> +++ b/linux/drivers/media/dvb/frontends/cx24123.c	Wed Jul 26 02:43:51 2006 -0400
> @@ -332,6 +332,12 @@ static int cx24123_set_fec(struct cx2412
>  	if ( (fec < FEC_NONE) || (fec > FEC_AUTO) )
>  		fec = FEC_AUTO;
>  
> +	/* Set the soft decision threshold */ 
> +	if(fec == FEC_1_2)
> +		cx24123_writereg(state, 0x43, cx24123_readreg(state, 0x43) | 0x01);
> +	else
> +		cx24123_writereg(state, 0x43, cx24123_readreg(state, 0x43) & ~0x01);	
> +
>  	switch (fec) {
>  	case FEC_1_2:
>  		dprintk("%s:  set FEC to 1/2\n",__FUNCTION__);
>
>
> ------------------------------------------------------------------------
>
> diff -r 265f2c767b45 linux/drivers/media/dvb/frontends/cx24123.c
> --- a/linux/drivers/media/dvb/frontends/cx24123.c	Mon Jul 24 15:19:37 2006 -0300
> +++ b/linux/drivers/media/dvb/frontends/cx24123.c	Wed Jul 26 04:17:46 2006 -0400
> @@ -45,9 +45,6 @@ struct cx24123_state
>  
>  	struct dvb_frontend frontend;
>  
> -	u32 lastber;
> -	u16 snr;
> -
>  	/* Some PLL specifics for tuning */
>  	u32 VCAarg;
>  	u32 VGAarg;
> @@ -234,7 +229,7 @@ static struct {
>  	{0x44, 0x00}, /* Constellation (default) */
>  	{0x45, 0x00}, /* Symbol count (default) */
>  	{0x46, 0x0d}, /* Symbol rate estimator on (default) */
> -	{0x56, 0x41}, /* Various (default) */
> +	{0x56, 0xc1}, /* Error Counter = Viterbi BER */
>  	{0x57, 0xff}, /* Error Counter Window (default) */
>  	{0x67, 0x83}, /* Non-DCII symbol clock */
>  };
> @@ -806,29 +801,13 @@ static int cx24123_read_ber(struct dvb_f
>  {
>  	struct cx24123_state *state = fe->demodulator_priv;
>  
> -	state->lastber =
> -		((cx24123_readreg(state, 0x1c) & 0x3f) << 16) |
> +	/* The true bit error rate is this value divided by
> +	   the window size (set as 256 * 255) */
> +	*ber = ((cx24123_readreg(state, 0x1c) & 0x3f) << 16) |
>  		(cx24123_readreg(state, 0x1d) << 8 |
> -		cx24123_readreg(state, 0x1e));
> -
> -	/* Do the signal quality processing here, it's derived from the BER. */
> -	/* Scale the BER from a 24bit to a SNR 16 bit where higher = better */
> -	if (state->lastber < 5000)
> -		state->snr = 655*100;
> -	else if ( (state->lastber >=   5000) && (state->lastber <  55000) )
> -		state->snr = 655*90;
> -	else if ( (state->lastber >=  55000) && (state->lastber < 150000) )
> -		state->snr = 655*80;
> -	else if ( (state->lastber >= 150000) && (state->lastber < 250000) )
> -		state->snr = 655*70;
> -	else if ( (state->lastber >= 250000) && (state->lastber < 450000) )
> -		state->snr = 655*65;
> -	else
> -		state->snr = 0;
> -
> -	dprintk("%s:  BER = %d, S/N index = %d\n",__FUNCTION__,state->lastber, state->snr);
> -
> -	*ber = state->lastber;
> +		 cx24123_readreg(state, 0x1e));
> +
> +	dprintk("%s:  BER = %d\n",__FUNCTION__,*ber);
>  
>  	return 0;
>  }
> @@ -846,19 +825,13 @@ static int cx24123_read_snr(struct dvb_f
>  static int cx24123_read_snr(struct dvb_frontend* fe, u16* snr)
>  {
>  	struct cx24123_state *state = fe->demodulator_priv;
> -	*snr = state->snr;
> +
> +	/* Inverted raw Es/N0 count, totally bogus but better than the
> +	   BER threshold. */
> +	*snr = 65535 - (((u16)cx24123_readreg(state, 0x18) << 8) |
> +			 (u16)cx24123_readreg(state, 0x19));
>  
>  	dprintk("%s:  read S/N index = %d\n",__FUNCTION__,*snr);
> -
> -	return 0;
> -}
> -
> -static int cx24123_read_ucblocks(struct dvb_frontend* fe, u32* ucblocks)
> -{
> -	struct cx24123_state *state = fe->demodulator_priv;
> -	*ucblocks = state->lastber;
> -
> -	dprintk("%s:  ucblocks (ber) = %d\n",__FUNCTION__,*ucblocks);
>  
>  	return 0;
>  }
> @@ -960,8 +933,6 @@ struct dvb_frontend* cx24123_attach(cons
>  	/* setup the state */
>  	state->config = config;
>  	state->i2c = i2c;
> -	state->lastber = 0;
> -	state->snr = 0;
>  	state->VCAarg = 0;
>  	state->VGAarg = 0;
>  	state->bandselectarg = 0;
> @@ -1014,7 +985,6 @@ static struct dvb_frontend_ops cx24123_o
>  	.read_ber = cx24123_read_ber,
>  	.read_signal_strength = cx24123_read_signal_strength,
>  	.read_snr = cx24123_read_snr,
> -	.read_ucblocks = cx24123_read_ucblocks,
>  	.diseqc_send_master_cmd = cx24123_send_diseqc_msg,
>  	.diseqc_send_burst = cx24123_diseqc_send_burst,
>  	.set_tone = cx24123_set_tone,
>
>
> ------------------------------------------------------------------------
>
> diff -r 265f2c767b45 linux/drivers/media/dvb/frontends/cx24123.c
> --- a/linux/drivers/media/dvb/frontends/cx24123.c	Mon Jul 24 15:19:37 2006 -0300
> +++ b/linux/drivers/media/dvb/frontends/cx24123.c	Wed Jul 26 01:57:22 2006 -0400
> @@ -933,6 +933,29 @@ static int cx24123_set_tone(struct dvb_f
>  	return 0;
>  }
>  
> +static int cx24123_tune(struct dvb_frontend* fe,
> +			struct dvb_frontend_parameters* params,
> +			unsigned int mode_flags,
> +			int *delay,
> +			fe_status_t *status)
> +{
> +	int retval = 0;
> +
> +	if (params != NULL)
> +		retval = cx24123_set_frontend(fe, params);
> +
> +	if (!(mode_flags & FE_TUNE_MODE_ONESHOT))
> +		cx24123_read_status(fe, status);
> +	*delay = HZ/10;
> +
> +	return retval;
> +}
> +
> +static int cx24123_get_algo(struct dvb_frontend *fe)
> +{
> +	return 1; //FE_ALGO_HW
> +}
> +
>  static void cx24123_release(struct dvb_frontend* fe)
>  {
>  	struct cx24123_state* state = fe->demodulator_priv;
> @@ -1019,6 +1042,8 @@ static struct dvb_frontend_ops cx24123_o
>  	.diseqc_send_burst = cx24123_diseqc_send_burst,
>  	.set_tone = cx24123_set_tone,
>  	.set_voltage = cx24123_set_voltage,
> +	.tune = cx24123_tune,
> +	.get_frontend_algo = cx24123_get_algo,
>  };
>  
>  module_param(debug, int, 0644);
>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
>
> linux-dvb@xxxxxxxxxxx
> http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb


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