STM32 - DMA write to GPIO causing a transfer error

I've been scratching my head all day trying to work this one out. My MCU is an STM32C071KBU6.

I am using a DMA to write to the GPIOA->BSRR register to look at signal timing with a scope. However, whenever the DMA is triggered it instantly raises the TEIFx. The odd bit is I can write to almost any other register using the same DMA setup, and it works, so I can verify my setup is ok. I have also manually written the same values to the BSRR register and it works, so it's not an address or data problem.

However, a DMA write to any GPIO register triggers an error. Is this a known problem?

This one is sneaky, because it is not explicitly mentioned anywhere in the reference manual (RM0490). The only clue given is by looking at the system architecture diagram on page 40:

For this chip, the GPIO ports are directly connected to the core, not the AHB bus, so the DMA has no access to them. It would seem that they opted for this layout to improve latency.

To trigger pins through DMA writes, you have to disable the preload of CCRx channels, and write values at the extremities (0 or ARR) to cause the outputs to flip accordingly.