STM32H7 Dual core - power consumption M4 vs M7

[Rverf.1]

Hello,

While I was looking for a new MCU, I came across STM32H7 dual core mcus, with M4 and M7.

I directly thought that it could be versatile for many usage, M7 for high performance, M4 to mix performances/ and power consumption (and from what I understood, "BAM" for low power data acquisition).

Note: For me, the power consumption is the main factor for choosing a processor (to make battery-powered data loggers)

However, reading the manual, it seems that M7 consumption is lower than M4 one. (or I missed some parameters in the documentation?)

Table 38: . Typical and maximum current consumption in Run mode, code with data processing

running from Flash memory, only Arm Cortex-M7 running, cache ON,

LDO regulator ON(1) :

VOS3 - 200MHZ (typical) : 34.5mA / 75mA (periph enabled)

Table 41. Typical and maximum current consumption in Run mode, code with data processing

running from Flash memory, only Arm Cortex-M4 running, ART accelerator ON,

LDO regulator ON(1)

VOS3 - 100MHZ (typical) : 35mA / 61mA (periph enabled)

Same consumption for a ratio of two in frequency.

So i am wondering, if I do not really need a dual core usage, could a M7 solo core is better (in ratio power/performances) ? Or did I really miss something here ?

Thank you for your help,

Romain

ps: link to the datasheet https://www.st.com/resource/en/datasheet/stm32h757xi.pdf

[Piranha]

> Same consumption for a ratio of two in frequency.

And probably a ratio of approximately 4 of data processing, because Cortex-M7 is dual-issue.

> For me, the power consumption is the main factor for choosing a processor (to make battery-powered data loggers)

What amount of data at what speed you have to process, that you are looking at such a powerful MCUs? Why not choose something from the L or G series?

[Rverf.1]

> And probably a ratio of approximately 4 of data processing, because Cortex-M7 is dual-issue.

Ok, so on an application with data acquisition (i2s/spi/sai,...) and some burst to save data on memory( SD), it could be a better solution to go on M7 ?

(It seem that batch acquisition mode is here for that ?)

> What amount of data at what speed you have to process,

It can be ~3MB/s (up to 2 terabytes on SD cards). Or sometimes, non-stop acquisition during several years at lower speed (~4kB/s).

I know that the need of performance is far between these two functionality, and I could change my MCU according to the usage, but it implies more development, more costs, ... If I can find something versatile that can adapt in most of the situations, it could be great.

> that you are looking at such a powerful MCUs? Why not choose something from the L or G series?

I first looked into F4 series (with Ethernet for data retrieving, and I plan to use HS-USB), but once here, i saw that on that dual-core processor, they can be separately powered or not by user. So why should I go on one core M4 if dual core M7/M4 can do the same, with same power-consumption, or eventually better with more performance ? (and the price per unit is absolutely not a problem for me).

Thank you for your answer, I am a bit lost in this jungle of MCUs.

[TDK]

Programming for dual-core adds quite a bit of overhead. It takes longer to develop. The H7 series is not made for power efficiency.

Unless you actually need the 480MHz clock, or the dual-core functionality, I'd strongly recommend the L4 (or L4+) or similar series. You don't need either of these to log at 3MB/s.

[Rverf.1]

> Programming for dual-core adds quite a bit of overhead.

That is, actually, the main reason too why I would not go on this family. But I would to be sure, it looks having great functionalities.

The L4 series, like the G4 lack of high speed connectivity. I need low power consumption for long time acquisition, but the maximum speed for data retrieving, that's why I consider going at least on F4 series.

(downloading hundreds gigabytes of data to a computer is already a pain with a (slow) 100MB Ethernet, that's why I don't want something too slow).

So, on F4 series (with Ethernet), power consumption is near twice better than the M4 on H7 series

(@90MHz 20mA / 43mA (periph enabled).

So, indeed, the H7 series may be a bit too much for my usage, but I still don't really understand what is the benefit of having a dual core with different families, the possibility to use one or the other independently, but with poor power performances on M4 core ?

[Piranha]

The 34,5/35 mA with peripherals disabled for M7/M4 at 200/100 MHz rises a suspicion on measurement correctness. When measuring one core, did they put the other core in sleep mode or was it busy looping in hard fault handler?