stm32f767 hardware jpeg decode header all zeros

[frackers]

Porting the basic JPEG_DecodingUsingFs_DMA from Discovery to custom hardware and I'm failing with the hardware JPEG decoder. The image decodes fine with the software decoder in STemWin and although I seem to be getting the HAL_JPEG_IRQHandler interrupt which indicates the header is ready, HAL_JPEG_GetInfo reads all zeros.

All initialisation is from CubeMX so of course I'm using the HAL library but I'm wondering if Cube is missing something - maybe initialising in a different order?

The same image decodes fine on the Discovery board by the way...

Hopefully this rings a bell with someone.