Stm32h5 usb hs and hexadeca/hspi/xspi spi

[etheory]

Dear ST,

Will you be releasing a variant of the H5 with both USB HS support and hexadeca/hspi/xspi support?

It seems confusing that your U5 series supports this but your higher speed more performance range doesn't.

Thanks.

[Soren Myllerup MIKKELSEN]

Hello @etheory 
For this kind of combination you can have a look at STM32H7R3, which offers HexadecaSPI (16-bit serial RA) + Octal Flash, and USB HS PHY. 

This demo shows USB DRD and DRP: https://www.youtube.com/watch?v=FpX9AdRocYQ

And its available as FS: https://www.st.com/en/microcontrollers-microprocessors/stm32h7r3-7s3.html# Teh

It all runs on the STM32H7S78-DK, which has a 16bit Serial PSRAM at 200MHz DTR + Octal SPI NOR flash at 200MHz DTR.

Best regards

Soren 

[etheory]

Thanks @Soren Myllerup MIKKELSEN,

I appreciate your reply.

The reason I want to use the H5 range is the lower power usage, and the fact it has onboard flash.

The issue with the STM32H7S and R series is that they use too much power and don't have onboard flash, and for the application I want, I'm after an energy efficient MCU with onboard flash, hexadeca support and USB HS. Unfortunately this is only available in the U5 range, but they aren't fast enough for the compute needed for my application, but the H5 is. Also, the H7S/R is overkill for my needs.

Thanks.

[Soren Myllerup MIKKELSEN]

Hello @etheory 
Which frequency are you looking for with Hexadeca SPI? For high speed its rarely seen on mainstream and entry-high performance MUCs. 

For sure the H7RS is not create for battery powered devices. H7R3 in VOS LOW with core freq at 300/400MHz, would still consume more than the H5 comparing all peripherals ON in Run mode. But we do see some applications where the MCU is not the main consumer of the battery. for example in Thermostats or Ebikes etc, which sometimes with on larger displays/resolutions. 

[etheory]

Your U5 line has excellent HSPI support up to 160MHz DDR/DTR in the BGA package along with HS USB.

Ideally the H5 line would also have HSPI support up to 200MHz DDR/DTR and HS USB.

It's quite surprising that your U5 line has such amazing support and peripherals, but the H5 is missing these.

The 160MHz core speed of the U5 is just a little too slow for the audio DSP I want to do, when the H5 is perfect, but lacks the periphals I want. Ideally I'd want a U5 that operates at H5 clock speeds and performance.

[Soren Myllerup MIKKELSEN]

Hello @etheory 
I can share that some of the motivations behind the U5+HSPI was driven by high-end smart watch makers. Which has both space and power constraints. I would still consider 16bit serial RAM (PSRAM, HyperRAM etc,) as an emerging tech and high-end, with Quad and Octo being much more general purpose and used. Please comment if you disagree.

That being said you should also have SDRAM in mind.

If you look at the theoretical BW on a 200MHz 16bit Serial RAM in DTR your are 800MB/S, but in a real application it will be much lower, depending on your type of read, write, RMW operations, burst size/lenght etc. 

The HSPI has more "dummy" cycles compared to an SDRAM. 

You can take a look here to better understand the actual performance for an 8 and 16bit serial RAM and flash: https://www.st.com/resource/en/application_note/an6062-introduction-to-stm32h7rx7sx-system-architecture-and-performance-stmicroelectronics.pdf

And have in mind that the actual performance of and SDRAM32bit 100MHz vs 200MHz HSPI DTR is very comparable in the end. 
Would you consider using 32bit SDRAM?

[etheory]

Thanks for your reply, that clarifies a lot.

From my research:
SDRAM is more expensive, uses more power, and requires far more pins and board space than HSPI.

The speed is definitely a factor, so what you say is compelling, but the extra complexity for the SDRAM just might not be worth it when I can get something similar that uses less power, costs less (for the same capacity) and has the throughput I need for my application.

My application is a battery or USB-powered DSP audio device, so power usage is paramount, and many SDRAM devices consume up to 1W current in use, vs HSPI/Hyperbus devices which consume on the order of 10's of mW. So on balance, SDRAM isn't an option for me. I'll have to start with the U5 devices to see if I can squeeze enough performance out of them, but it's not ideal.

[Soren Myllerup MIKKELSEN]

Good morning @etheory 

Yes, i agree on your points. 

If you look for more DMIPS with a Cortex-M7, you could look at the STM32H7A3, its not a low power device but it brings some lower power capabilities compared to other high perf MCUs. On top you can connect up to 2x OctoSPI memories, so could also be 2xSerial 8bit RAMs at 100-140MHz, bringing more performance but also more complex memory/code partitioning.