volkmarnissen
commented
9 months ago I just found out, that the work around is not really working.
Whenever a call to readHoldingRegister terminates with ETIMEDOUT and you close the connection afterwards, the resource is still locked. If you do a successful readHoldingRegister after ETIMEDOUT Exception, you can close it without locking the resource. So, The ETIMEDOUT exception doesn't unlock the port properly.
import ModbusRTU from 'modbus-serial'
import Debug from "debug"
import { ReadRegisterResult } from 'modbus-serial/ModbusRTU';
const debug = Debug("modbusreopen");
Debug.enable('modbusreopen')
const client = new ModbusRTU();
let count = 0;
connect()
function open() {
debug("closed " + (client.isOpen ? "is open" : "is closed"))
if (count++ < 4) {
debug("open")
client.connectRTU("/dev/ttyUSB0", { baudRate: 9600 }).then(read).catch((e) => {
debug("Error connected" + e)
});
}
else {
debug("exit()");
process.exit()
}
}
function read() {
debug("opened " + (client.isOpen ? "is open" : "is closed"))
client.setID(7)
client.setTimeout(100)
debug("reading")
client.readHoldingRegisters(1, 1).then(close).catch((e) => {
debug("failed to read " + JSON.stringify(e))
if (e.errno && e.errno == "ETIMEDOUT") {
client.setID(2)
debug("read from existing device " + count)
if (count == 0)
client.readHoldingRegisters(1, 1).then((r) => {
debug("read result: " + JSON.stringify(r))
close()
}).catch((e) => {
debug("failed to read from existing device" + JSON.stringify(e))
close()
})
else {
debug("No successful read after timeout")
close()
}
}
})
}
// open connection to a serial port
function close(result?: ReadRegisterResult) {
if (result)
debug(JSON.stringify(result))
debug("will close " + (client.isOpen ? "is open" : "is closed"))
if (client.isOpen) {
debug("call close")
client.close(open)
}
else {
debug("read again")
open()
//setTimeout(open, 10)
}
}
function connect() {
client.connectRTU("/dev/ttyUSB0", { baudRate: 9600 }).then(read).catch((e) => {
debug("Error connected")
console.log(e)
});
}
this produces this output:
modbusreopen opened is open +0ms
modbusreopen reading +1ms
modbusreopen failed to read {"name":"TransactionTimedOutError","message":"Timed out","errno":"ETIMEDOUT"} +101ms
modbusreopen read from existing device 0 +1ms
modbusreopen read result: {"data":[1],"buffer":{"type":"Buffer","data":[0,1]}} +41ms
modbusreopen will close is open +0ms
modbusreopen call close +0ms
modbusreopen closed is closed +8ms
modbusreopen open +0ms
modbusreopen opened is open +2ms
modbusreopen reading +0ms
modbusreopen failed to read {"name":"TransactionTimedOutError","message":"Timed out","errno":"ETIMEDOUT"} +100ms
modbusreopen read from existing device 1 +1ms
modbusreopen No successful read after timeout +0ms
modbusreopen will close is open +0ms
modbusreopen call close +0ms
modbusreopen closed is closed +0ms
modbusreopen open +0ms
modbusreopen Error connectedError: Error Resource temporarily unavailable Cannot lock port +2ms
teddy1565
When you execute ModbusRTU.open/ModbusRTU.close multiple times, it will work only for the first open call. The second open call will fail with "Error Resource temporarily unavailable Cannot lock port".
You can see in the debug log, that second open call does not trigger "Creating poller". May be this is the reason.
As a work around, you can always create a new ModbusRTU and call connectRTU instead of calling ModbusRTU.open.
Here is how to reproduce it:
This is the debug output