50.1.2 Bootloader Entry Mechanisms
Default Entry Mechanism:
- The Bootloader will run automatically if there is no valid application firmware. Firmware is considered valid if the first word at the application start address is not 0xFFFFFFFF.
- Normally this word contains the initial stack pointer value, so it will never be 0xFFFFFFFF unless the device is erased
Trigger Entry Mechanism:
- External trigger:
- The Boot pin should be used to trigger the Bootloader after reset (See the following table)
- Drive the respective Boot pin to a low state, then reset the device. Upon reset, the Bootloader runs and checks the status of the Boot pin. If the status of the pin is low, the Bootloader enters the firmware upgrade mode.
- Bootloader Trigger Pattern in
SRAM:
- The application can trigger the Bootloader by writing a Bootloader trigger pattern to the first four words (1 word = 4 bytes) of SRAM (0x20000000), then resetting the device
- Upon reset, the Bootloader runs and checks the first four words of the SRAM for the presence of the Bootloader trigger pattern. If found, the Bootloader enters the firmware upgrade mode.
- To invoke the Bootloader, the trigger pattern is 0x5048434D
| Trigger mode | Trigger method |
|---|---|
| Boot pin | PA27 = Active low (Internal pull-up is enabled. No hardware/software de-bouncing is implemented.) |
| SRAM trigger pattern (0x20000000) | SRAM Word[0] = 0x5048434D SRAM Word[1] = 0x5048434D SRAM Word[2] = 0x5048434D SRAM Word[3] = 0x5048434D |