Merge pull request #8 from dok-net/resp_timeout

Employ total response timeout (fix #7)

library.json

@@ -1,6 +1,6 @@
 {
     "name": "esp_sds011",
-    "version": "1.0.0",
+    "version": "1.0.1",
     "description": "ESP8266/ESP32 library for the SDS011 particulate matter sensor",
     "keywords": [
       "sds011"

library.properties

@@ -1,5 +1,5 @@
 name=esp_sds011
-version=1.0.0
+version=1.0.1
 author=Dirk O. Kaar
 maintainer=Dirk O. Kaar <[email protected]>
 sentence=ESP8266/ESP32 library for the SDS011 particulate matter sensor.

src/Sds011.cpp

@@ -129,10 +129,6 @@ bool Sds011::query_data_auto(int& pm25, int& pm10) {
     return true;
 }
 
-bool Sds011::timeout() {
-    return _timeout;
-}
-
 bool Sds011::crc_ok() {
     uint8_t crc = 0;
     for (int i = 2; i < 8; ++i) {
@@ -170,18 +166,15 @@ void Sds011::_send_cmd(enum Command cmd, const uint8_t* data, uint8_t len) {
     _out.write(_buf, sizeof(_buf));
 }
 
-int Sds011::_read_byte(long unsigned deadline) {
-    uint32_t start = millis();
-    while (!_out.available()) {
-        if (millis() - start < deadline) {
-            delay(1);
-            continue;
-        }
-        _timeout = true;
-        return -1;
+// _read_byte returns timeout (-1) regardless of pending data
+// if _read_response_deadline has expired.
+int Sds011::_read_byte() {
+    for (;;) {
+        const uint32_t deadlineExpired = millis() - _read_response_start;
+        if (deadlineExpired >= _read_response_deadline) return -1;
+        if (_out.available()) break;
+        delay(1);
     }
-
-    _timeout = false;
     return _out.read();
 }
 
@@ -193,22 +186,25 @@ void Sds011::_clear_responses() {
 
 bool Sds011::_read_response(enum Command cmd) {
     uint8_t i = 0;
-    const long unsigned deadline = 1000;
+    int recv;
+    _read_response_start = millis();
     while (i < 3) {
-        _buf[i] = _read_byte(deadline);
-        if (timeout()) { break; }
+        recv = _read_byte();
+        if (0 > recv) { break; }
+        _buf[i] = recv;
         switch (i++) {
         case 0: if (_buf[0] != 0xAA) i = 0; break;
         case 1: if (_buf[1] != ((cmd == CMD_QUERY_DATA) ? 0xC0 : 0xC5)) i = 0; break;
         case 2: if (cmd != CMD_QUERY_DATA && _buf[2] != cmd) i = 0; break;
         }
     }
     for (i = 3; i < 10; i++) {
-        if (timeout()) { break; }
-        _buf[i] = _read_byte(deadline);
+        if (0 > recv) { break; }
+        recv = _read_byte();
+        _buf[i] = recv;
     }
 
-    bool succ = !timeout() && _buf[9] == 0xAB;
+    bool succ = !(0 > recv) && _buf[9] == 0xAB;
     return succ;
 }
 
@@ -288,7 +284,7 @@ bool Sds011Async_Base::query_data_auto_async(int n, int* pm25_table, int* pm10_t
             query_data_auto_start = millis();
             query_data_auto_deadline = (rampup_s - dataAutoCnt) * 1000UL;
             onReceive([this](int avail) {
-                unsigned long deadlineExpired = millis() - query_data_auto_start;
+                uint32_t deadlineExpired = millis() - query_data_auto_start;
                 if (deadlineExpired < query_data_auto_deadline) {
                     _get_out().flush();
                     return;

src/Sds011.h

@@ -69,7 +69,6 @@ class Sds011 {
     bool query_data(int& pm25, int& pm10);
     bool query_data(int& pm25, int& pm10, int n);
     bool query_data_auto(int& pm25, int& pm10);
-    bool timeout();
     bool crc_ok();
 
     bool filter_data(int n, const int* pm25_table, const int* pm10_table, int& pm25, int& pm10);
@@ -85,14 +84,15 @@ class Sds011 {
     };
 
     void _send_cmd(enum Command cmd, const uint8_t* buf, uint8_t len);
-    int _read_byte(long unsigned deadline);
+    int _read_byte();
     String _buf_to_string(uint8_t size);
     void _clear_responses();
     bool _read_response(enum Command cmd);
 
     Stream& _out;
     uint8_t _buf[19];
-    bool _timeout = false;
+    uint32_t _read_response_start;
+    static constexpr uint32_t _read_response_deadline = 1010;
 
     unsigned rampup_s = 10;
 };