jankae/LibreVNA
1
0
Fork 0
mirror of https://github.com/jankae/LibreVNA.git synced 2026-04-07 15:33:51 +00:00
Code Issues Projects Releases Packages Wiki Activity

Basic DFT spectrum analysis working

Browse source
This commit is contained in:
Jan Käberich 2020-11-07 00:50:59 +01:00
parent f889ec854b
commit ce475fa042
27 changed files with 1313 additions and 563 deletions
Download patch file Download diff file Expand all files Collapse all files

48
Software/VNA_embedded/Application/Drivers/Si5351C.cpp
View file

@ -315,29 +315,31 @@ void Si5351C::FindOptimalDivider(uint32_t f_pll, uint32_t f, uint32_t &P1,
// see https://www.silabs.com/documents/public/application-notes/AN619.pdf (page 3/6)
uint32_t a = f_pll / f;
int32_t f_rem = f_pll - f * a;
uint32_t best_b, best_c;
uint32_t best_deviation = UINT32_MAX;
for (uint32_t c = (1UL << 20) - 1; c >= (1UL << 19); c--) {
uint32_t guess_b = (uint64_t) f_rem * c / f;
for (uint32_t b = guess_b; b <= guess_b + 1; b++) {
int32_t f_div = (uint64_t) f * b / c;
uint32_t deviation = abs(f_rem - f_div);
if (deviation < best_deviation) {
best_b = b;
best_c = c;
best_deviation = deviation;
if (deviation == 0) {
break;
}
}
}
if (best_deviation == 0) {
break;
}
}
LOG_DEBUG(
"Optimal divider for %luHz/%luHz is: a=%lu, b=%lu, c=%lu (%luHz deviation)",
f_pll, f, a, best_b, best_c, best_deviation);
// always using the highest modulus divider results in less than 1Hz deviation for all frequencies, that is good enough
uint32_t best_c = (1UL << 20) - 1;
uint32_t best_b = (uint64_t) f_rem * best_c / f;
// uint32_t best_deviation = UINT32_MAX;
// for (uint32_t c = (1UL << 20) - 1; c >= (1UL << 19); c--) {
// uint32_t guess_b = (uint64_t) f_rem * c / f;
// for (uint32_t b = guess_b; b <= guess_b + 1; b++) {
// int32_t f_div = (uint64_t) f * b / c;
// uint32_t deviation = abs(f_rem - f_div);
// if (deviation < best_deviation) {
// best_b = b;
// best_c = c;
// best_deviation = deviation;
// if (deviation <= 3) {
// break;
// }
// }
// }
// if (best_deviation <= 3) {
// break;
// }
// }
// LOG_DEBUG(
// "Optimal divider for %luHz/%luHz is: a=%lu, b=%lu, c=%lu (%luHz deviation)",
// f_pll, f, a, best_b, best_c, best_deviation);
// convert to Si5351C parameters
uint32_t floor = 128 * best_b / best_c;
P1 = 128 * a + floor - 512;