Ensuring that both the hardware and software of a Bluetooth chip are operating correctly.
Bluetooth device manufacturing involves ensuring the quality and performance of devices. One key test that’s used to verify the functionality of Bluetooth devices is the Bluetooth PCM lookback test, which ensures that both the hardware and software of the Bluetooth chip are operating correctly.
A Bluetooth pulse code modulation (PCM) lookback test primarily verifies the functionality of the Bluetooth chip’s PCM interface. The test involves looping back the SCO/eSCO data on the Bluetooth chip side, allowing for the testing of the chip’s PCM interface without the need for external equipment (see Figure 1).
Fig. 1: Schematic of a normal path vs. Loopback-enabled Bluetooth PCM test.
As shown in Table 1, this is done by changing the vendor command Write_PCM_Loopback_Mode. The Loopback_Mode parameter can be set to either 0x00 to disable the loopback or 0x01 to enable it. The command returns a status value, which is 0x00 if the command is successful and a non-zero value if it fails.
Table 1: Command to configure Bluetooth device
| Command | OGF | OCF | Parameters | Return |
| Write_PCM_Loopback_Mode | 0x3F | 0x0024 | Loopback_Mode | Status |
Loopback_Mode:
0x00 – Disable loopback
0x01 – Enable loopback
Status:
0x00 – Success,
otherwise – Fail
To run this test, use the related PCM/I2S parameters. The following examples provided are for different configurations, including Bluetooth PCM at 8K and 16K sample rates, as well as Bluetooth I2S at 16K sample rate.
Bluetooth PCM @8K+master:
./mbt input_command 1cfc050001000101
./mbt input_command 24fc0101
Bluetooth PCM @16K+master:
./mbt input_command 7efc03010200
./mbt input_command 6dfc0400010102
./mbt input_command 1cfc050002000101
./mbt input_command 1efc050000030000
./mbt input_command 24fc0101
Bluetooth I2S @16K+master:
./mbt input_command 7efc03010200
./mbt input_command 6dfc0401010102
./mbt input_command 24fc0101
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