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ddi_compute_wrpll: Rework the logic around r2 and n2 a bit

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Let's not use the 2K variants of the frequencies it does not help
in anything here and the explanations are hopefuly more understandable
this way.

On top of that, I noticed that we can just compute the desired min/max
boundaries for r2 and n2, so use that instead of the two tests to
discard out of range values.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
This commit is contained in:
Damien Lespiau 2013-05-02 16:33:56 +01:00
parent bb1dfd5613
commit 4897ac41da
1 changed files with 25 additions and 30 deletions
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55
tests/ddi_compute_wrpll.c
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@ -12,14 +12,6 @@
#define P_MAX 64
#define P_INC 2
#define R2_MIN 5
#define R2_MAX 256
#define R2_INC 1
#define N2_MIN 5
#define N2_MAX 256
#define N2_INC 1
/* Constraints for PLL good behavior */
#define REF_MIN 48
#define REF_MAX 400
@ -189,33 +181,36 @@ wrpll_compute_rnp(int clock /* in Hz */,
}
/*
* Ref * 2000 = LC_FREQ_2K / R, where Ref is the actual reference input
* seen by the WR PLL. In particular:
* REF_MIN <= LC_FREQ_2K / (R * 2000) and
* REF_MAX >= LC_FREQ_2K / (R * 2000).
* Eliminating fractions gives:
* 2000 * REF_MAX * R >= LC_FREQ_2K >= 2000 * R * REF_MIN, R2 = 2*R
* Ref = LC_FREQ / R, where Ref is the actual reference input seen by
* the WR PLL.
*
* We want R so that REF_MIN <= Ref <= REF_MAX.
* Injecting R2 = 2 * R gives:
* REF_MAX * r2 > LC_FREQ * 2 and
* REF_MIN * r2 < LC_FREQ * 2
*
* Which means the desired boundaries for r2 are:
* LC_FREQ * 2 / REF_MAX < r2 < LC_FREQ * 2 / REF_MIN
*
*/
for (r2 = R2_MIN; r2 <= R2_MAX; r2 += R2_INC) {
if (1000 * REF_MAX * r2 < LC_FREQ_2K)
continue;
if (1000 * REF_MIN * r2 > LC_FREQ_2K)
continue;
for (r2 = LC_FREQ * 2 / REF_MAX + 1;
r2 <= LC_FREQ * 2 / REF_MIN;
r2++) {
/*
* VCO is N * Ref, that is: VCO = N * LC_FREQ_2K / (R * 2000).
* VCO = N * Ref, that is: VCO = N * LC_FREQ / R
*
* Once again, VCO_MAX >= N * LC_FREQ_2K / (R * 2000) >= VCO_MIN,
* or: VCO_MAX * R * 2000 >= N * LC_FREQ_2K >= VCO_MIN * R * 2000,
* where R2=2*R and N2=2*N
* Once again we want VCO_MIN <= VCO <= VCO_MAX.
* Injecting R2 = 2 * R and N2 = 2 * N, we get:
* VCO_MAX * r2 > n2 * LC_FREQ and
* VCO_MIN * r2 < n2 * LC_FREQ)
*
* Which means the desired boundaries for n2 are:
* VCO_MIN * r2 / LC_FREQ < n2 < VCO_MAX * r2 / LC_FREQ
*/
for (n2 = N2_MIN; n2 <= N2_MAX; n2 += N2_INC) {
if (VCO_MAX * r2 * 2000 < n2 * LC_FREQ_2K)
continue;
if (VCO_MIN * r2 * 2000 > n2 * LC_FREQ_2K)
continue;
for (n2 = VCO_MIN * r2 / LC_FREQ + 1;
n2 <= VCO_MAX * r2 / LC_FREQ;
n2++) {
for (p = P_MIN; p <= P_MAX; p += P_INC)
wrpll_update_rnp(freq2k, budget,