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r82xx: improve tuner precision 

Improve tuner precision by calculating the VCO divisor at full precision, not
at kHz resolution. Also replace the manual divison loop with a simpler
fixed-point calculation.
This commit is contained in:
Oliver Jowett 2014-08-23 22:08:23 +01:00 committed by Sultan Qasim Khan
parent af33886796
commit f5978e8871
1 changed files with 24 additions and 21 deletions
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45
src/tuner_r82xx.c
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@ -429,12 +429,11 @@ static int r82xx_set_pll(struct r82xx_priv *priv, uint32_t freq)
int rc, i;
unsigned sleep_time = 10000;
uint64_t vco_freq;
uint32_t vco_fra; /* VCO contribution by SDM (kHz) */
uint32_t vco_min = 1770000;
uint32_t vco_max = vco_min * 2;
uint32_t freq_khz, pll_ref, pll_ref_khz;
uint16_t n_sdm = 2;
uint16_t sdm = 0;
uint64_t vco_div;
uint32_t vco_min = 1770000; /* kHz */
uint32_t vco_max = vco_min * 2; /* kHz */
uint32_t freq_khz, pll_ref;
uint32_t sdm = 0;
uint8_t mix_div = 2;
uint8_t div_buf = 0;
uint8_t div_num = 0;
@ -446,7 +445,6 @@ static int r82xx_set_pll(struct r82xx_priv *priv, uint32_t freq)
/* Frequency in kHz */
freq_khz = (freq + 500) / 1000;
pll_ref = priv->cfg->xtal;
pll_ref_khz = (priv->cfg->xtal + 500) / 1000;
rc = r82xx_write_reg_mask(priv, 0x10, refdiv2, 0x10);
if (rc < 0)
@ -495,8 +493,24 @@ static int r82xx_set_pll(struct r82xx_priv *priv, uint32_t freq)
return rc;
vco_freq = (uint64_t)freq * (uint64_t)mix_div;
nint = vco_freq / (2 * pll_ref);
vco_fra = (vco_freq - 2 * pll_ref * nint) / 1000;
/* We want to approximate:
* vco_freq / (2 * pll_ref)
*
* in the form:
* nint + sdm/65536
*
* where nint,sdm are integers and 0 < nint, 0 <= sdm < 65536
*
* Scaling to fixed point and rounding:
*
* vco_div = 65536*(nint + sdm/65536) = int( 0.5 + 65536 * vco_freq / (2 * pll_ref) )
* vco_div = 65536*nint + sdm = int( (pll_ref + 65536 * vco_freq) / (2 * pll_ref) )
*/
vco_div = (pll_ref + 65536 * vco_freq) / (2 * pll_ref);
nint = (uint32_t) (vco_div / 65536);
sdm = (uint32_t) (vco_div % 65536);
if (nint > ((128 / vco_power_ref) - 1)) {
fprintf(stderr, "[R82XX] No valid PLL values for %u Hz!\n", freq);
@ -511,7 +525,7 @@ static int r82xx_set_pll(struct r82xx_priv *priv, uint32_t freq)
return rc;
/* pw_sdm */
if (!vco_fra)
if (sdm == 0)
val = 0x08;
else
val = 0x00;
@ -520,17 +534,6 @@ static int r82xx_set_pll(struct r82xx_priv *priv, uint32_t freq)
if (rc < 0)
return rc;
/* sdm calculator */
while (vco_fra > 1) {
if (vco_fra > (2 * pll_ref_khz / n_sdm)) {
sdm = sdm + 32768 / (n_sdm / 2);
vco_fra = vco_fra - 2 * pll_ref_khz / n_sdm;
if (n_sdm >= 0x8000)
break;
}
n_sdm <<= 1;
}
rc = r82xx_write_reg(priv, 0x16, sdm >> 8);
if (rc < 0)
return rc;