what is DETACH-ATTACH sequence?

[Subhash42]

Hello, I'm writing a code on DFU  for FX3,then I got stuck with a process named DETACH-ATTACH sequence,

what is DETACH-ATTCAH sequence and how to implement it in FX3?

Thank You.

[Rashi_Vatsa · Accepted solution]

Hello,

I understand that you are referring to USB IF defined DFU spec and want to implement that for FX3. Please confirm.

Assuming that you are referring to DFU spec by USB IF, as per the spec, the device should first enumerate with a DFU class-interface descriptor and associated functional descriptor embedded within the device’s normal run-time descriptors  (application specific descriptors)indicating that the device is capable of DFU.

When host application starts the update process, following is the sequence

- Host issues DFU_DETACH request on EP0

- The host issues a USB reset to the device

- FX3 should handle this USB reset request by re enumerating (i.e. disconnecting USB and connecting it again) with DFU descriptors set only

You can refer to section 5 of the spec https://www.usb.org/sites/default/files/DFU_1.1.pdf for more details