PDM: fix setGain() for dfsdm

facchinm · facchinm · commit 2bb5b88d82bd · 2024-09-02T16:00:20.000+02:00
If the gain was too high, the right bit shift RecBuff[i] >> attenuation would result in undefined behaviour https://www.iso-9899.info/n1570.html#6.5.7 Take the chance to also fix the (approximate) conversion from gain (in dB) to bit shift
diff --git a/libraries/PDM/src/STM32H747_dfsdm/audio.c b/libraries/PDM/src/STM32H747_dfsdm/audio.c
@@ -391,7 +391,10 @@ int py_audio_init(size_t channels, uint32_t frequency)
 
 void py_audio_gain_set(int gain_db)
 {
-  attenuation = 8 - gain_db;
+  attenuation = 8 - (gain_db / 3);
+  if (attenuation < 0) {
+    attenuation = 0;
+  }
 }
 
 void py_audio_deinit()

Original file line number	Diff line number	Diff line change
`@@ -391,7 +391,10 @@ int py_audio_init(size_t channels, uint32_t frequency)`
`391`	`391`
`392`	`392`	`void py_audio_gain_set(int gain_db)`
`393`	`393`	`{`
`394`		`- attenuation = 8 - gain_db;`
	`394`	`+ attenuation = 8 - (gain_db / 3);`
	`395`	`+ if (attenuation < 0) {`
	`396`	`+ attenuation = 0;`
	`397`	`+ }`
`395`	`398`	`}`
`396`	`399`
`397`	`400`	`void py_audio_deinit()`