The boot strap loader (BSL) enables configuration of the device as well as programming of the device memory through a serial interface such as UART, I²C, or USB. Access to the device memory and configuration through the BSL is protected by a 256-bit user-defined password, and it is possible to completely disable the BSL in the device configuration, if desired. The BSL is enabled by default from TI to support use of the BSL for production programming.

Using the BSL can involve the following pins, depending on the method:

• UART interface: BSLRX and BSLTX signals
• I²C interface: BSLSCL and BSLSDA signals
• USB interface: BSLUSB_DM and BSLUSB_DP
• Additional methods: BSL_invoke and NRST signals may be used for controlled invokation of the bootloader by an external host

If enabled, the BSL may be invoked (started) in the following ways:

• The BSL is invoked during the boot process if the BSL_invoke pin state matches the defined BSL_invoke logic level. If the device fast boot mode is enabled, this invocation check is skipped. An external host can force the device into the BSL by asserting the invoke condition and applying a reset pulse to the NRST pin to trigger a BOOTRST, after which the device will verify the invoke condition during the reboot process and start the BSL if the invoke condition matches the expected logic level.
• The BSL is automatically invoked during the boot process if the reset vector and stack pointer are left unprogrammed. As a result, a blank device from TI will invoke the BSL during the boot process without any need to provide a hardware invoke condition on the BSL_invoke pin. This enables production programming using just the serial interface signals.
• The BSL may be invoked at runtime from application software by issuing a SYSRST with BSL entry command.

For a complete description of the BSL functionality and command set, see the MSPM0 boot strap loader user's guide.