53.1.2 Bootloader Entry Mechanisms
Default Entry Mechanism:
- The Bootloader will run
automatically if there is no valid application firmware. The 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
0xFFFFFFFFunless the device is erased
Trigger Entry Mechanism:
- External trigger:
- The Boot pin must be used to trigger the Bootloader after reset, refer to the table below.
- 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 with a length of four
words (1 word = 4 bytes) to the SRAM location
0x20001000, then resetting the device. The Bootloader will not be using the initial 4 KB of SRAM as it will be cleared by the BOOTROM at reset. Therefore, the bootloader trigger pattern has to be stored at0x20001000of the SRAM. - Upon reset, the Bootloader
runs and checks the first four words of the SRAM location
0x20001000for 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.
- The application can trigger
the Bootloader by writing a Bootloader trigger pattern with a length of four
words (1 word = 4 bytes) to the SRAM location
| Trigger mode | Trigger method |
|---|---|
| Boot pin | PB08 = Active-low (Internal pull-up is enabled. No hardware or software debouncing is implemented.) |
SRAM trigger pattern
(0x20001000) | SRAM Word[0] = 0x5048434D
|