STM32H7 periodical TIM triggered SPI transfer w/o DMA?

[MSZB]

On a STM32H745ZI-Q - Board I want to create periodical 4-byte SPI transfers  triggered by a timer. 

So far I got this working the following way:

TIM triggers DMA
DMA initiates the SPI transfer.

However, the SPI transfer timing (CS low) has a high jitter of 100 ns, which is not acceptable.

To reduce the jitter: Is there any known way to trigger the SPI transfer start directly by a timer on this specific MCU (from reading the RM, I don't think so)? 

The data to be transfered could be written to the SPI FIFO in advance by an ISR triggered with a proper delay. 

[LCE]

At least for some other H7s (H723, 725, 733, 735) the 960 MHz after DIVN1 would be too much.
Maybe you are above the limit and CubeMX doesn't recognize it?

[MSZB]

> At least for some other H7s (H723, 725, 733, 735) the 960 MHz after DIVN1 would be too much.
> Maybe you are above the limit and CubeMX doesn't recognize it?

For H745 the limit is 960 MHz (from STM32H745xI/G, table 59)

[waclawek.jan]

> HSE is used, 8 MHz MCO from ST-LINK.

As I've said above, the primary clock there is *not* HSE but HSI.

> It's jitter is roughly 1 ns.

Cycle-to-cycle jitter of HSI may be way better than long-term jitter.

Try to switch STLink to output the HSE-originated 25MHz/3 clock, and change the target's clock accordingly.

JW