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| == Issue Identification: ==
| | {{Migrating|https://smartpossdk.gitbook.io/cloudpossdk/faq/usb-serial-port/close-serial-after-disconnect}} |
| During the operation of an application that reads from a serial port, if an error message stating "Level 3 halted" appears in the log, it typically indicates that the serial port cable has been disconnected.
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| == Recommended Solution: ==
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| # '''Immediate Action upon Error Detection:'''
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| #* Upon encountering this error, the application should immediately close the serial port.
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| # '''Attempt to Reopen the Serial Port:'''
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| #* After closing, the application should try to reopen the serial port.
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| # '''Handling Persistent Connection Issues:'''
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| #* If the application fails to reopen the serial port, check and reconnect the serial port cable as necessary.
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| == Java SDK Implementation: ==
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| * '''Catching DeviceException during Serial Port Read:'''
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| ** In the Java SDK, you can handle this situation by catching the DeviceException when performing serial port read operations.
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| == Code Snippet Example: ==
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| <syntaxhighlight lang="java">
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| try {
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| byte[] readBytes = new byte[256];
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| SerialPortOperationResult serialPortOperationResult = serialPortDevice.waitForRead(readBytes.length, TimeConstants.FOREVER);
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| int resultCode = serialPortOperationResult.getResultCode();
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| if (resultCode == SerialPortOperationResult.SUCCESS) {
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| byte[] data = serialPortOperationResult.getData();
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| Logger.debug("read success:" + new String(data));
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| } else if (resultCode == SerialPortOperationResult.LEVEL_3_HALTED) {
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| Logger.debug("devices is gone, please close it first, then open it again.");
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| serialPortDevice.close();
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| }
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| } catch (DeviceException e) {
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| e.printStackTrace();
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| }
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| </syntaxhighlight >
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| This approach ensures the application can effectively manage unexpected disconnections and attempts to re-establish the serial port connection.
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