Solve race condition with arduino IDE monitoring serial port
I encountered a race condition upon which, even though the udev rules were working and uploads succeed, the serial monitor can not re-establish communications. If the serial monitor is left open when doing an upload the error shown is: [...] Copying data from PC to DFU device Starting download: [##################################################] finished! state(8) = dfuMANIFEST-WAIT-RESET, status(0) = No error condition is present Done! Resetting USB to switch back to runtime mode Waiting for /dev/ttyACM0 serial...Done processing.app.SerialException: Error opening serial port '/dev/ttyACM0'. Try consulting the documentation at http://playground.arduino.cc/Linux/All#Permission at processing.app.Serial.<init>(Serial.java:145) at processing.app.Serial.<init>(Serial.java:82) at processing.app.SerialMonitor$4.<init>(SerialMonitor.java:101) at processing.app.SerialMonitor.open(SerialMonitor.java:101) at processing.app.AbstractMonitor.resume(AbstractMonitor.java:104) at processing.app.Editor.resumeOrCloseSerialMonitor(Editor.java:2218) at processing.app.Editor.access$2200(Editor.java:79) at processing.app.Editor$DefaultExportHandler.run(Editor.java:2196) at java.lang.Thread.run(Thread.java:748) Error opening serial port '/dev/ttyACM0'. Try consulting the documentation at http://playground.arduino.cc/Linux/All#Permission I traced it to the device being opened prior to the permissions/ownership changes. When testing via -c the upload script waits for the character device creation, but at that point the udev rules have not changed the permissions. By testing the readability of the device via the -r test, we wait until the new permissions have been applied. I imagine this is specific to the Linux kernel and the speed of the machine being used. In my case: arduino-1.8.5 Linux 4.4.0-98-generic #121-Ubuntu SMP but the change should work on any system with proper udev rules / permissions.
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@ -42,7 +42,7 @@ fi
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echo -n Waiting for ${dummy_port_fullpath} serial...
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COUNTER=0
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while [ ! -c ${dummy_port_fullpath} ] && ((COUNTER++ < 40)); do
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while [ ! -r ${dummy_port_fullpath} ] && ((COUNTER++ < 40)); do
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sleep 0.1
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done
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