nRF5 DFU over serial

[Phil]

We are implementing a DFU controller to perform DFU over serial for the nRF52832.

Our reference is the nRF5 SDK v15.3.0 DFU Serial documentation (Nordic/SDK/nRF_SDK_15.3.0_docs/nrf5/lib_dfu_transport_serial.html).

The documentation has a message sequence chart that describes Transfer of an Init Packet, and Transfer of a firmware Image.

I'm find the description regarding transfer of a firmware image a bit ambiguous. It says the firmware image is split up into several data objects that are transferred consecutively.  For example if the image is 10k and the maximum object size is 4k, then 3 data objects must be transferred.   Presumably two 4k objects followed by a 2k object.

1) Is the Select command required at the start of each data object, or just once when the firmware image transfer is started?

2) Is the execute command sent at the end of each data object, or just once at the end of the entire firmware image transfer?

2) Once all the data has been transferred (3 data objects in the example) is it necessary to do one more Select command immediately followed by an execute command?

3) At what point does the boot-loader know the entire image has been downloaded and start the application.  Does it attempt to do this on every execute command?

In our case we have found the Select response returns a maximum object size of 4096 bytes.  Our firmware image is not a multiple of 4096 bytes, so I my difficulty is understanding what happens when the last data object, which is less than the maximum object size,  is transferred.

[Phil]

Yes, thanks.  I had found that after looking through the boot-loader.  Your code sets the data object length of the last object to the length of the remaining firmware image bytes.  It also looks like the code in the boot-loader requires the last data object length to be equal to the length of the remaining bytes. I might be wrong here.  However, the issue is that I was requesting a data object size less than 4096 bytes that was not the last data object.  The SDK15.3.0 DFU documentation is not clear on this.

My problem is that the firmware size is in the init packet, which sent to the boot-loader successfully.  However, I was down-loading a test image while developing my DFU protocol code.  This is writing a generated test pattern into the nRF52 ROM and the total length was much less than the firmware image length.

By the way, we are implementing the DFU controller as a state machine.  We process the response to every command sent to the boot-loader. We set the PRN to 1 at the start to get a response to every write data packet.  That way the DFU is self-timing and the offset returned in the response to write commands keeps track of the progress. Also there is no need to request a CRC just before the execute command as this is returned in the write data response.

Thanks for your help.  Much appreciated.

[Hung Bui]

I'm glad that you figured out most of the stuff. Let me know if you still have any issue transferring the image.