From 34c070ed426e529b0cac9c8e3c26b2b69947a156 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20Hamal=20Dvo=C5=99=C3=A1k?= <mordae@anilinux.org>
Date: Sat, 24 Feb 2024 22:26:09 +0100
Subject: [PATCH] Fix max amplitude formula and DC bias removal
---
src/main.c | 34 +++++++++++++++++++++++++---------
1 file changed, 25 insertions(+), 9 deletions(-)
diff --git a/src/main.c b/src/main.c
index 645ef36..3ffd53a 100644
--- a/src/main.c
+++ b/src/main.c
@@ -551,7 +551,11 @@ static void rf_rx(void)
int64_t dcI = 0, dcQ = 0;
- const int amp_max = (float)CLK_SYS_HZ / BANDWIDTH * DECIMATION * 3.0 / 4.0 / 2.0;
+ /*
+ * CLK / BW for oversampling, but 1/2 for the -1/0/0/1 PIO outcomes.
+ * Signal can get outside due to DC offset compensation.
+ */
+ const int amp_max = CLK_SYS_HZ / 2 / BANDWIDTH * DECIMATION;
while (true) {
if (multicore_fifo_rvalid()) {
@@ -619,16 +623,28 @@ static void rf_rx(void)
I = lpIa3 / LPF_SIZE;
Q = lpQa3 / LPF_SIZE;
- int64_t I64 = (int64_t)I << 32;
- int64_t Q64 = (int64_t)Q << 32;
-
- dI += (I64 - dcI) >> 32;
- dQ += (Q64 - dcQ) >> 32;
-
- dcI = ((dcI << 20) - dcI + I64) >> 20;
- dcQ = ((dcQ << 20) - dcQ + Q64) >> 20;
+ dI += I;
+ dQ += Q;
}
+ dcI = ((dcI << 13) - dcI + (dI << 19)) >> 13;
+ dcQ = ((dcQ << 13) - dcQ + (dQ << 19)) >> 13;
+
+ dI -= dcI >> 19;
+ dQ -= dcQ >> 19;
+
+ if (dI > amp_max)
+ dI = amp_max;
+
+ if (dI < -amp_max)
+ dI = -amp_max;
+
+ if (dQ > amp_max)
+ dQ = amp_max;
+
+ if (dQ < -amp_max)
+ dQ = -amp_max;
+
*blockptr++ = 127 * dI / amp_max;
*blockptr++ = 127 * dQ / amp_max;
}