Replacing a Serial Cable with Bluetooth: Reliability and Recovery Tests - Yenra

Define the application’s contract before testing

The Bluetooth Serial Port Profile defines emulated serial cable connections over RFCOMM. The application still determines what the arriving bytes mean. A measurement line, barcode or command may need a delimiter, fixed length, checksum or explicit acknowledgment.

Write down electrical interface, baud rate, data bits, parity, stop bits and flow control, then follow the serial-adapter compatibility and loopback guide. Use a harmless bench setup or simulator. Equipment that controls hazardous motion or a safety function needs its own engineering validation; this generic data test cannot authorize a retrofit.

Define acceptance before running it: maximum response time, whether every record must arrive, how duplicates are recognized and what should happen after loss of the link. Distinguish “bytes sent” from “record accepted by the destination application.”

Exercise a small repeatable dataset

Create a sequence of recognizable test records, such as TEST-001 through TEST-020, each with the application’s expected terminator. Keep a sent log and a received log. Record the test rate, exact bytes or encoding, and the point at which the receiving application acknowledges or saves a record.

On small screens, scroll the table sideways to read all columns.

Run the same known input through the wired baseline and the wireless setup. Keep endpoint software and serial settings constant. If the application itself transforms identifiers, inspect its saved output as well as the terminal log.

Budget serial time before blaming radio delay

Digi’s serial-settings reference explains the 9600 8N1 notation and the need to match the connected device’s settings.

Illustrative calculation: an asynchronous 8N1 serial setting uses one start bit, eight data bits and one stop bit per byte. A 100-byte message therefore requires 1,000 serial bits. At 9,600 bits per second, the nominal serialization time at that port is 1,000 ÷ 9,600 = 0.1042 seconds, about 104 milliseconds.

This excludes buffering, radio scheduling, retransmission, peer-side serialization and application work. Some stages may overlap; adding two port times blindly is also unreliable. Measure from the event your requirement actually names, such as source record creation to destination acceptance. A 50-millisecond whole-message deadline already conflicts with the example’s source-port serialization alone.

Record timestamps on a common clock where possible. If separate clocks are used, document synchronization error before interpreting a small latency difference.

Make reconnection prove data recovery

In the isolated test, interrupt the link using the documented disconnect method. Record which test identifiers were outstanding, reconnect and compare the final application log with the sent log. Repeat a host or adapter restart only where the bench setup allows it. Verify that any partial record is rejected or handled according to the application’s specification.

Fictional result: 20 records are sent; the received log has 20 lines, but TEST-008 appears twice and TEST-009 is absent. The count matches while the data is incomplete. A useful acceptance check compares identifiers and content, not only line totals.

For commands with real effects, avoid automatic retries until the application specifies acknowledgment and duplicate protection. A lost response can mean either the command failed or it succeeded and its acknowledgment was lost. Record a clear pass/fail result for each scenario and leave unresolved behavior visible.