DFU_DNLOAD request commands

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DocID017068 Rev 4

The DFU Leave operation is effectively executed only when a DFU_GETSTATUS request is

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

has occurred. After this operation, the device performs the following:

•

it disconnects itself

•

it initializes the registers of the peripherals used by the bootloader to their default reset

values

•

it initializes the user application’s main stack pointer

•

it jumps to the memory location programmed in the received ‘address pointer + 4’,

which corresponds to the address of the application’s reset handler

For example if the received address is 0x0800 0000, the bootloader will jump to the

memory location programmed at address 0x0800 0004.

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

programmed.

The address pointer has to be set (using the Set Address Pointer command) before

launching the Leave DFU routine, otherwise, the bootloader will jump to the default address

(internal Flash memory start address: 0x08000000).

The address pointer can also be set through the last Write Memory operation: if a download

operation is performed, the address pointer used for this download will be stored and used

later for the jump.

Note:

If the address pointer points to an address that does not contain executable code, then the

device is reset and, depending on the state of the boot pins, may re-enter the bootloader

mode.

Since the bootloader DFU application is not manifestation-tolerant, the device will not be

able to respond to host requests after a manifestation phase is completed.

A second DFU_GETSTATUS request may also be issued (if the device is still connected) to

check if the command has been correctly executed. If the device fails to execute the

command it returns an error status (depending on the error type).

Note:

1

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

point to the application address.

2

When performing a jump from the bootloader to a loaded application code which uses the

USB IP, the user application has to disable all pending USB interrupts and reset the core

before enabling interrupts. Otherwise, a pending interrupt (issued from the bootloader code)

may interfere with the user code and cause a functional failure. This procedure is not

needed after exiting the system memory boot mode.