From 9a7e710a2c7d4ba01b303e242edb56fdf1715c4f Mon Sep 17 00:00:00 2001
From: dakkar <dakkar@thenautilus.net>
Date: Sun, 27 Mar 2022 13:20:10 +0100
Subject: low power pm

---
 pm.h | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/pm.h b/pm.h
index 634c1b4..9c8a508 100644
--- a/pm.h
+++ b/pm.h
@@ -4,11 +4,27 @@
 
 #include "data.h"
 
+/*
+start measuring
+
+read once, stop, sleep
+
+ready?
+   if (now-last measurements) < read_interval, no
+   else: start measuring, return ready status
+ */
+
 class PM {
 private:
   uint8_t auto_clean_days;
+  unsigned long last_measurment_millis;
+  unsigned long read_interval_millis;
 public:
-  PM(uint8_t acd=4) :auto_clean_days(acd) {}
+  PM(uint8_t acd=4, unsigned long ri=30000) :
+    auto_clean_days(acd),
+    last_measurment_millis(0),
+    read_interval_millis(ri)
+  {}
 
   void start() {
     // this will try to re-init Wire, emit a warning, and carry on
@@ -37,6 +53,16 @@ public:
     uint16_t data_ready;
     int16_t ret;
 
+    // have we read recently?
+    unsigned long now=millis();
+    // that first check is in case of overflow & rollover
+    if (now > last_measurment_millis && (now - last_measurment_millis) < read_interval_millis) {
+      return false;
+    }
+
+    sps30_wake_up();
+    sps30_start_measurement();
+
     ret = sps30_read_data_ready(&data_ready);
     if (ret < 0) {
       Serial.print("PM reading data-ready flag error: ");
@@ -58,6 +84,11 @@ public:
     if (ret <0) {
       Serial.print("PM reading measurement error: ");
       Serial.println(ret);
+      return;
     }
+
+    last_measurment_millis = millis();
+    sps30_stop_measurement();
+    sps30_sleep();
   }
 };
-- 
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