AN3155 datasheet(18/37 Pages) STMICROELECTRONICS

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Bootloader command set

AN3155

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DocID17066 Rev 6

The host sends bytes as follow to the STM32:

3.6

Write Memory command

The Write Memory command is used to write data to any valid memory address (see note

below) i.e. RAM, Flash memory, option byte area...

When the bootloader receives the Write Memory command, it transmits the ACK byte to the

application. After the transmission of the ACK byte, the bootloader waits for an address (4

bytes, 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 avoid writing inopportunely in this area.

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:

•

gets a byte, N, which contains 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 the STM32 is 256 bytes.

If the Write Memory command is issued to the Option byte area, all options are erased

before writing the new values, and at the end of the command the bootloader generates a

system Reset to take into account the new configuration of the option byte.

Note:

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

by the bootloader firmware.

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

returned when the start address is invalid.

Byte 1:

0x21

Byte 2:

0xDE

Wait for ACK

Byte 3 to byte 6: start address

byte 3: MSB

byte 6: LSB

Byte 7:

checksum: XOR (byte 3, byte 4, byte 5, byte 6)

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