Description
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Basic Infos
I have a MT681 power meter with an IR output connected to the UART. The meter sends bursts of 500 bytes every 1200ms @9600bps. So one burst lasts about 500ms.
Hardware
Hardware: WemosD1 mini
Core Version: 2.4.0rc2
Description
When the RX bursts are present upon boot, the ESP fails to connect to wifi. It does connect eventually but it takes it a unpredictable amount of time, mostly about 10min.
Obviously the watchdog kicked in. There is some output:
ets Jan 8 2013,rst cause:4, boot mode:(3,6)
wdt reset
load 0x4010f000, len 1384, room 16
tail 8
chksum 0x2d
csum 0x2d
v0c897c37
~ld
Workaround:
Set UART mode to tx only, RXbuffersize =0. Wait for connect , then adjust the buffer size and the uart mode according to your needs.
Settings in IDE
Module: Wemos D1mini
Flash Size: 4MB
CPU Frequency: 80Mhz
Flash Mode: ?qio?
Flash Frequency: ?40Mhz?
Upload Using: SERIAL (tried OTA too)
Reset Method: power cycle
Sketch
The sketch makes the ESP send itself some bytes over the serial. RX1 sends to swapped RX0.
You need a wire between D4 (TX1) and D7 (swapped RX0) for this.
If the wire is present the watchdog will kick in.
If you remove the wire, the ESP will start.
Observation 1: yield(); while receiving helps a lot. But how can you yield() if you do not know when bytes are coming ?
Observation 2: If the size of the RX buffer is left at the default value, things don't work either.
#include <ESP8266WiFi.h>
//#include <WiFiClient.h>
//#include <ESP8266WebServer.h>
const char* ssid = "...";
const char* password = "...";
unsigned long startuptime;
void setup(void){
Serial.setRxBufferSize(400);
Serial.begin(115200);
Serial.println("\n\nstart...");
pinMode(D4,OUTPUT); // check the wire bridge
digitalWrite(D4,0);
if (digitalRead(D7)==0)
Serial.println("D4 D7 wire bridge detected.");
else
Serial.println("NO wire bridge detected. Put it between D4 and D7");
Serial.flush(); // force ouput
delay(100); // wait for output
Serial.swap(); // route the RX pin to D7
Serial1.begin(115200);
for (int i = 0; i<500; i++)
{
Serial1.write(i);
//yield(); // this fixes the issue (and breaks the example)
// but this is not the point. Trouble occurs when recieving, not sending.
// sending here is only done for the sake of simplicity.
// besides: sending 500 bytes takes 39ms
// now: pull the wire and watch the ESP run ;-)
}
startuptime=millis();
WiFi.begin(ssid, password); // now try to connect
while (WiFi.status() != WL_CONNECTED) {
delay(1);
Serial1.write(0x55);
}
Serial.swap();
}
void loop(void){
Serial.println("Wifi connected. Startup time: " + String(millis()-startuptime) +"ms");
Serial.println("Bytes in buffer: " + String(Serial.available()));
for (;;) delay(1000);
}Output:
start...
D4 D7 wire bridge detected.
ets Jan 8 2013,rst cause:4, boot mode:(3,6)
wdt reset
load 0x4010f000, len 1384, room 16
tail 8
chksum 0x2d
csum 0x2d
v0c897c37
~ld
edit 2017-12-22:
- added wdt output
- added example