AN4286 datasheet(18/38 Pages) STMICROELECTRONICS

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AN4286

Bootloader command set

2.6

Go command

The Go command is used to execute the downloaded code or any other code by branching

to an address specified by the application. When the bootloader receives the Go command,

it transmits the ACK byte to the application. After transmission of the ACK byte, the

bootloader waits for an address (4 bytes, byte 1 being the address MSB and byte 4 the LSB)

and a checksum byte, then it checks the received address. If the address is valid and the

checksum is correct, the bootloader transmits an ACK byte; otherwise it transmits a NACK

byte and aborts the command.

When the address is valid and the checksum is correct, the bootloader firmware performs

the following.

•

Initializes the registers of the peripherals used by the bootloader to their default reset

values.

•

Initializes the user application’s main stack pointer.

•

Jumps to the memory location programmed in the received ‘address + 4’ (which

corresponds to the address of the application’s reset handler). For example, if the

received address is 0x08000000, the bootloader jumps to the memory location

programmed at address 0x08000004.

In general, the master should send the base address where the application to jump to is

programmed.

Note:

The jump to the application works only if the user application sets the vector table correctly

to point to the application address.

The master sends bytes as follows to the STM32.

•

Start Of Frame: 0x5A

•

Byte 1: 0x21

•

Byte 2: 0xDE

•

Wait for ACK (as described in section 1)

•

Byte 3 to byte 6: start address

–

byte 3: MSB

–

byte 6: LSB

•

Byte 7: checksum: XOR (byte 3, byte 4, byte 5 and byte 6)

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