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DEVICE FIRMWARE UPGRADE (DFU) IMPLEMENTATION IN ST7 USB DEVICES

Figure 2. DFU Mode Entry Mechanism

3.3 FLASH SECTOR MANAGEMENT

In order for the DFU mode entry mechanism described above to function correctly, it is neces-

sary to place the firmware routines in the right sectors.

Basically, Sector 0 contains all routines that must be preserved during DFU erasing and pro-

gramming. It principally contains the USB standard Library and the DFU layer routines.

Note: Application routines or constants can also be present in this sector, but in this case they

cannot be updated in DFU mode.

The Sectors 1 and 2 contain all routines and data that can be erased or changed in DFU

mode. They contain the Application routines and the “jump table” (see below).

The DFU_DETACH request decoding must also be present in these sectors. We can imagine

a “one shot DFU”, where the DFU_DETACH request decoding is not implemented in the new

firmware just downloaded (software protection). The only way to recover is by using a Hard-

ware switch (see Figure 2).

3.3.1 SECTOR 1 AND 2 INTEGRITY CHECK

As we have seen previously, we need to check if Sectors 1 and 2 are correct before calling the

main application routine. This will insure that these sectors are not corrupted due bad erasing

or bad programming. This check is not described in the DFU specification. and it can be easily

removed from the DFU protocol.

Sectors 1 & 2

DFU Process

Main Application

Main DFU

MCU Reset

are OK ?

Yes

No

DFU_Detach

Forced DFU Mode Entry

Sector 0

Sectors

1 and 2

Code, Checksum,

CRC, ...

(Controlled by hardware switch)