MS/BS Power Control Loop: Fix downscaling averaging bug

The bug showed up in previous commit and is fixed in this commit. It can
be seen how rounding error is carried over time in the average
measurement, and affects final values.

Change-Id: I680d1c94bd4bae179b14b26662a819fa1462a5c8

3 files changed, 7 insertions, 7 deletions

diff --git a/tests/power/ms_power_loop_test.c b/tests/power/ms_power_loop_test.c
index b9d68670..5f833290 100644
--- a/tests/power/ms_power_loop_test.c
+++ b/tests/power/ms_power_loop_test.c
@@ -204,11 +204,11 @@ static void test_pf_algo_ewma(void)
 	/* Avg[t] = (0.2 * 40) + (0.8 * 29.60) = RXLEV 31.68 (-78.32 dBm),
 	 * but due to up-/down-scaling artefacts we get the following:
 	 *   Avg100[t] = Avg100[t - 1] + A * (Pwr - Avg[t] / 100)
-	 *   Avg100[t] = 2960 + 20 * (40 - (2960 / 100))
-	 *   Avg100[t] = 2960 + 20 * (40 - 29)
-	 *   Avg[t] = 3180 / 100 = 31.80 */
+	 *   Avg100[t] = 2960 + 20 * (40 - ((2960+50) / 100)) <- HERE we lose 0.1: (2960+50) / 100) = 30.1
+	 *   Avg100[t] = 2960 + 20 * (40 - 30) <- HERE we lose 20*0.1 = 2.0! (upscaled, hence we lose finally 2.0/100=0.2)
+	 *   Avg[t] = (3160) / 100 = 31.60*/
 	apply_power_test(lchan, -70, good_lqual, 1, 9); /* RXLEV 40 */
-	CHECK_RXLEV_AVG100(31.80);
+	CHECK_RXLEV_AVG100(31.60);
 
 	mp->ewma.alpha = 70; /* 30% smoothing */
 	lchan->ms_power_ctrl.current = 15;
diff --git a/tests/power/ms_power_loop_test.err b/tests/power/ms_power_loop_test.err
index 8ab64198..8f588821 100644
--- a/tests/power/ms_power_loop_test.err
+++ b/tests/power/ms_power_loop_test.err
@@ -23,8 +23,8 @@
 (bts=0,trx=0,ts=0,ss=0) Lowering MS power control level 14 (2 dBm) => 15 (0 dBm): ms-pwr-lvl[curr 14, max 0], RSSI[curr -40, avg -47, thresh -75..-75] dBm, C/I[curr 14, avg 14, thresh 12..16] dB
 (bts=0,trx=0,ts=0,ss=0) Keeping MS power at control level 15 (0 dBm): ms-pwr-lvl[curr 15, max 2], RSSI[curr -75, avg -75, thresh -75..-75] dBm, C/I[curr 14, avg 14, thresh 12..16] dB
 (bts=0,trx=0,ts=0,ss=0) Raising MS power control level 15 (0 dBm) => 13 (3 dBm): ms-pwr-lvl[curr 15, max 2], RSSI[curr -90, avg -78, thresh -75..-75] dBm, C/I[curr 14, avg 14, thresh 12..16] dB
-(bts=0,trx=0,ts=0,ss=0) Raising MS power control level 13 (4 dBm) => 11 (8 dBm): ms-pwr-lvl[curr 13, max 2], RSSI[curr -90, avg -81, thresh -75..-75] dBm, C/I[curr 14, avg 14, thresh 12..16] dB
-(bts=0,trx=0,ts=0,ss=0) Raising MS power control level 11 (8 dBm) => 9 (12 dBm): ms-pwr-lvl[curr 11, max 2], RSSI[curr -70, avg -79, thresh -75..-75] dBm, C/I[curr 14, avg 14, thresh 12..16] dB
+(bts=0,trx=0,ts=0,ss=0) Raising MS power control level 13 (4 dBm) => 11 (8 dBm): ms-pwr-lvl[curr 13, max 2], RSSI[curr -90, avg -80, thresh -75..-75] dBm, C/I[curr 14, avg 14, thresh 12..16] dB
+(bts=0,trx=0,ts=0,ss=0) Raising MS power control level 11 (8 dBm) => 9 (11 dBm): ms-pwr-lvl[curr 11, max 2], RSSI[curr -70, avg -78, thresh -75..-75] dBm, C/I[curr 14, avg 14, thresh 12..16] dB
 (bts=0,trx=0,ts=0,ss=0) Keeping MS power at control level 15 (0 dBm): ms-pwr-lvl[curr 15, max 2], RSSI[curr -50, avg -50, thresh -75..-75] dBm, C/I[curr 14, avg 14, thresh 12..16] dB
 (bts=0,trx=0,ts=0,ss=0) Keeping MS power at control level 15 (0 dBm): ms-pwr-lvl[curr 15, max 2], RSSI[curr -50, avg -50, thresh -75..-75] dBm, C/I[curr 14, avg 14, thresh 12..16] dB
 (bts=0,trx=0,ts=0,ss=0) Raising MS power control level 15 (0 dBm) => 13 (4 dBm): ms-pwr-lvl[curr 15, max 2], RSSI[curr -110, avg -92, thresh -75..-75] dBm, C/I[curr 14, avg 14, thresh 12..16] dB
diff --git a/tests/power/ms_power_loop_test.ok b/tests/power/ms_power_loop_test.ok
index 8c92b037..27992b14 100644
--- a/tests/power/ms_power_loop_test.ok
+++ b/tests/power/ms_power_loop_test.ok
@@ -62,7 +62,7 @@ lchan_ms_pwr_ctrl(RxLvl=-90 dBm) returns 1 (expected 1)
 	Avg[t] is RxLev 29.60 (expected 29.60)
 lchan_ms_pwr_ctrl(RxLvl=-70 dBm) returns 1 (expected 1)
 	MS current power 11 -> 9 (expected 9)
-	Avg[t] is RxLev 31.80 (expected 31.80)
+	Avg[t] is RxLev 31.60 (expected 31.60)
 lchan_ms_pwr_ctrl(RxLvl=-50 dBm) returns 0 (expected 0)
 	MS current power 15 -> 15 (expected 15)
 	Avg[t] is RxLev 60.00 (expected 60.00)