Clarification on 128-bit Flash Programming Time on STM32U575 (Normal vs Burst Mode)

[msalik]

I’m working with the STM32U575 and I found in the datasheet that the Flash programming time for a 128-bit (16-byte) write is:

• 118 µs in normal mode

• 48 µs in burst mode

(From Table 86: Flash memory characteristics)

Before finalizing our design, I need clarification on how these timing values apply in practice:

1. Is the 128-bit programming time the total time per write operation, or is there additional overhead (such as “opening/closing a page” or internal setup time) that needs to be added?

2. If I write multiple 128-bit words sequentially, do I pay the 118/48 µs each time, or is there any extra per-sequence delay?

3. Are there any alignment requirements beyond 128-bit (16-byte) alignment?

4. Do these programming times assume the Flash page is already erased?

We plan to evaluate whether the internal Flash write speed will meet our throughput needs, so I want to be sure I understand all timing components correctly.

Thanks!

[TDK]

There's no reason to doubt the datasheet here.

1) Flash needs unlocked. Small cost. If your program does other things between writes or is otherwise slow, that will be additional overhead. This is only a measure of programming time. Generally the overhead is minimal compared to programming time. Ensure next write is ready to go when the first finishes.

2) Each time. See (1).

3) No.

4) Programming time doesn't include the time to erase. Programming non-erased flash is not useful as this will trigger ECC.

[TDK]

On second look, there is reason to doubt the datasheet. The typical value should not match maximum value.

And 128 bit * 118 us max is 7.552 s max to write 1 MB, while the 1 MB program time says 7.710 s typical. So those are off. Same thing with 8 kB time.

I'd characterize it yourself if it matters. Or open an ST support ticket.