pd_mon: Add iir filter to voltage readings

- analog wdg behaviour is unchanged

src/laser_diode/ld_pwr_exc_protector.rs

@@ -47,6 +47,7 @@ pub struct LdPwrExcProtector {
     calibrated_vdda: u32,
     offset: u32,
     prev_samples: [u16; 32],
+    prev_iir_sample: u16,
     ptr: u16,
 }
 
@@ -148,6 +149,7 @@ impl LdPwrExcProtector {
                 calibrated_vdda: 3300,
                 offset: offset,
                 prev_samples: [0; 32],
+                prev_iir_sample: 0,
                 ptr: 0,
             });
         }
@@ -198,7 +200,9 @@ impl LdPwrExcProtector {
                     samples += wdg.prev_samples[idx] as u32;
                 }
                 samples = samples >> 5;
-                wdg.alarm_status.v = LdPwrExcProtector::convert_sample_to_volt(samples as u16);
+
+                wdg.prev_iir_sample = (7 * wdg.prev_iir_sample + samples as u16) >> 3;
+                wdg.alarm_status.v = LdPwrExcProtector::convert_sample_to_volt(wdg.prev_iir_sample);
             }
             return wdg.alarm_status.v;
         }