I've been playing around with the GPSDTx board for a few days now and I've gotten the interface with the DAC sorted out pretty well. It's a pretty simple interface but I didn't implement it quite as efficiently as I could have so that will be something to address in the next board revision.

I still have lots to do to get a more smoothly running product, not the least of which is getting the SysTick turned off. The auto-generated STM32Cube startup code turned that on and it's also included a bunch of extraneous libraries and things that I don't need or want yet depend on the SysTick so, right now, I get glitches every 1mS when updating the DAC due to the SysTick interrupt firing and doing what ever it does.