Project migration from STM32F405RG to STM32G473RE

[Greg H]

STM32G4 CPU speed. I am migrating a project from the STM32F405RG to the STM32G473RE. System clock frequency for both is 168MHz. I have found the code runs at about half speed on the STM32G473 and I would like to know why and how to fix it.

The STM32G473 flash is in dual bank mode and has data cache, instruction cache and prefetch enabled with 8 wait states. Will switching to single bank mode, increasing flash data width from 64 bit to 128 bit to match the STM32F405, restore the speed or is there more likely another cause? Will running the code in SRAM restore speed, as I would prefer to stay in dual bank mode.

[Amel NASRI]

Hello @Greg H​ ,

If you use your STM32G4 with a flash configured in single bank mode, you need to consider that at 168 MHz: on STM32F4 you have 5 wait states, while on STM32G4 you need 8 wait states.

While being the default one, the dual bank configuration is recommended for Read-while-write (RWW) mainly.

-Amel

[Greg H · Accepted solution]

Speed Problem Fixed.

By moving the main interrupt service routine to CCM RAM I obtained considerable speed improvement. Here are the computation time comparisons for the ISR:

STM32F405 from FLASH: 7 microseconds

STM32G473 from FLASH in dual bank mode: 14 microseconds

STM32G473 from CCM RAM: 6 microseconds

The code is heavy with branching so I suspect the combination of increased wait states and the reduced FLASH bus width contributed to the problem.

Thank you everyone for your comments

GH

[waclawek.jan]

> The code is heavy with branching so I suspect the combination of increased wait states and the reduced FLASH bus width contributed to the problem.

That nicely rounds up the "0-wait-state execution from Flash memory," marketing lie, perpetuated in the 'F4/'G4 datasheet's very first line.

Thanks for coming back with the results. Please select your post as Best so that the thread is marked as resolved.

JW

[Igor Cesko]

The STM32G4 performance was improved - because Flash speed was re-characterized and now the Flash can operate up to 34MHz speed => 4 wait states at 170MHz. See updated reference manual RM0440. More about STM32G4 performance improvement is in https://community.st.com/s/feed/0D53W000004JX9fSAG?t=1588146144942 .

Regards

Igor

[hamdi.najoua]

​Hello all,

Please refer to this post:

https://community.st.com/s/question/0D53W000005qUp6SAE/stm32g4-family-performance-enhancement

Best regards,

Najoua.