[issue #914] _P053_PMSx003 Dust Sensor looses sync

[TD-er]

• Use peek instead of read, to make sure a complete packet is in the buffer.
• Flush buffer after processing a packet.
• Increased software serial buffer to the size of 3 packets.
• Peek (+ read garbage) 10 times per second to get the buffer in sync to start with start byte of packet.
• Decent delete + clean up of software serial allocation when changing settings (prevent memory leak)
• Move log String allocation to inside scope of function, not permanent allocated.
• Split into separate functions to make it better readable.

[uzi18]

It is better to check also if dummy (marker) is exactly 0x424D, if not we don't need to try calculate checksum.

Looks like problem was because always take 2 bytes from buffer and datagram has even bytes so it is impossible to find sync if miss one byte.

[TD-er]

That's a good suggestion. (it was past 2am)
Will try that later today.

[micropet]

OK, test begins.

[TD-er]

@micropet OK to merge it?

[micropet]

Unfortunately, no. There were about 60 minutes of data delivered.
Now nothing is coming out.

[TD-er]

But it is not worse than before?
When I merge it, then others can also test. Just to get an idea what's going on. (don't have one of those sensors myself, for the next few weeks)

[micropet]

Yes you are right. This version also runs longer than the old version.

[micropet]

serialReadPMValue.zip

I've been running this version on an ESP32 and STMF4 board for many months now.

She has never failed. Maybe it gives you an idea.

#include "serialReadPMValue.h"
uint16_t p01 = 0; //define PM1.0 value of the air detector module
uint16_t p25 = 0; //define PM2.5
uint16_t p10 = 0; //define PM10
#define receiveDatIndex 32
uint8_t receiveDat[receiveDatIndex];

int length = serialRead(Serial1,receiveDat,receiveDatIndex,5); //change the serial port:Serial1,Serial2..
int checkSum=checkValue(receiveDat,receiveDatIndex);

if(length&&checkSum)
{
p01=transmitPM01(receiveDat); // count PM1.0 value of the air detector module
p25=transmitPM2_5(receiveDat); // count PM2.5 value of the air detector module
p10=transmitPM10(receiveDat); // count PM10 value of the air detector module
}