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 at intel.com>
---
tests/ddi_compute_wrpll.c | 55 +++++++++++++++++++++--------------------------
1 file changed, 25 insertions(+), 30 deletions(-)
diff --git a/tests/ddi_compute_wrpll.c b/tests/ddi_compute_wrpll.c
index c0fd08c..bdde61c 100644
--- a/tests/ddi_compute_wrpll.c
+++ b/tests/ddi_compute_wrpll.c
@@ -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,
--
1.8.1.4
