Help debugging weird SOF timing

[fantacuits]

I've been working on a USB device where precise timing is critical, and I keep running into inconsistencies with start of frame (SOF) detection. Even though the device enumerates correctly, the SOF events sometimes appear delayed or are missed entirely, which throws off the timing for downstream processes. I've double checked signal integrity on the USB lines and verified my firmware ISR timing, but the problem persists. It seems like there might be something subtle in how the host controller or the USB stack handles SOF under certain load conditions. I'm also wondering if USB jitter or buffer handling could be contributing.
Anyone can help? I'd greatly appreciate

 

[KatrinaTeller]

Not gonna lie, I'm still learning USB stuff, but from what I read SOF isn't meant to be exact timing... just a marker. I'd use it to realign things once in a while, but I'd let a crystal timer run the show. Otherwise you're always chasing jitter that you can't really fix.

 

[justjack]

@fantacuits , the thing is that host controllers and USB stacks aren't perfectly real time, so some jitter or missed events is normal even if enumeration

 

[itsmeroseyy_]

ESOF interrupts can help monitor any SOFs that get missed and match them up against the expected timing, but only if they are supported.