DocID017068 Rev 4

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AN3156

DFU_DNLOAD request commands

25

5.1

Write memory

The Write memory operation is selected when wValue > 1.

The host requests the device to receive a specified number of data bytes (wLength) to load

them into valid memory addresses (see note) in internal Flash memory, embedded RAM or

option bytes.

Note:

Refer to Section 4: DFU_UPLOAD request commands for more details about the valid

memory addresses for the device you are using.

The allowed number of bytes to be written depends on the memory target:

•

For the internal Flash memory and embedded RAM: write size can be from 2 to 2048

bytes

•

For the option bytes: write size should be equal to the option byte block size

•

For other memory locations, refer to the section "Important considerations” depending

on the product in AN2606.

Note:

A different write size is possible for the option bytes but it is recommended to write the entire

block at a time in order to ensure data integrity. When the target is the option byte area, the

address pointer must always be the start address of the option bytes, otherwise, the request

is not performed.

The Write memory operation is effectively executed only when a DFU_GETSTATUS request

is issued by the host. If the status returned by the device is not dfuDNBUSY, then an error

has occurred.

A second DFU_GETSTATUS request is needed to check if the command has been correctly

executed, except when the destination is the option byte area (in this case the device is

immediately reset after the write operation completion). If the received address is wrong or

unsupported, the device status is then (Status = dfuERROR, State = errTARGET).

The address, to which the host requests to write data, is computed using the value of

wBlockNumber (wValue) and the address pointer according to the same formula as for an

upload request:

Address = ((wBlockNum – 2) × wTransferSize) + Addres_Pointer, where:

–

wTransferSize: length of the data buffer sent by the host

–

wBlockNumber: value of the wValue parameter

If the Flash Read Protection is enabled, the Write memory operation is not performed and

the returned device status is (Status = dfuERROR, State = errVENDOR) whatever the target

(internal Flash, embedded RAM or option 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 bytes.

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.