AN3262

Bootloader command set

Doc ID 17845 Rev 2

19/27

Figure 21.

3.6

RAM, Flash memory or Option byte area.

the application. After sending the ACK byte, the bootloader waits for an address (4 bytes,

where Byte 1 is the address MSB and Byte 4 is the LSB) and a checksum byte, it then

checks the received address. For the Option byte area, the start address must be the base

address of the Option byte area (see note) to prevent unwanted writing to this area.

Note:

1

Write operations to Flash memory/SRAM must be word (32-bit) aligned and data should be

in multiples of four bytes. If less data are written, the remaining bytes should be filled by

0xFF.

If the received 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:

●

receives a byte (N) containing the number of data bytes to be received,

●

receives the user data ((N + 1) bytes) and the checksum (XOR of N and of all data

bytes),

●

programs the user data to memory starting from the received address,

●

at the end of the command, if the write operation was successful, the bootloader

transmits the ACK byte; otherwise it transmits a NACK byte to the application and

aborts the command.

The maximum length of the block to be written for STM32W devices is 96 bytes.

before writing the new values.

Note:

1

When writing to the RAM, you should take care not to overlap the first RAM memory used by

the bootloader firmware.

2

No error is returned when performing write operations on write-protected sectors.

3

No error is returned when the start address is invalid.