STM32H755, is the clock too slow?

[halbeeee]

Hello everyone, I'm working on an STM32H755BI (industrial temperature range), and i'm quite disappointed by the maximum clock reachable from the system.

As can be seen, the MCU can reach up to 480MHz in the core M7 and 240MHz in the core M4.

After months of develpment, a firmware package update blocked me the VOS0 and VOS1, and in fact reading the user manual those modes are unavailable on my package, so i reduced to 300MHz and 150MHz

Today, with an update of cube MX, this error appeared in the clock tree:

And in fact by reading the datasheet APB4 is limited to 100MHz.

Reducing APB4 to 100MHZ could not be a big deal, but the real problem is that considering the clock distribution in the previous image the clock of the APB4 is the same clock of the M4 (CPU2).

Does this means that i bought a 480+240MHz and i'm forced to use it at 300+100 after more than a year of development?

[AScha.3]

@Pavel A. ,

Right ! Thats it - what is "allowed" by STM and what the user is choosing...

I think, the H7 have a reliability problem : if high temperature, no long life.

And high clk makes more temp... so its up to the user, to decide : live long or be fast at hi temp.

A little bit like in "Blade Runner" --- you know about the life time of the replicants ? 

[Tesla DeLorean]

@AScha.3 Perhaps I should have been clearer, where do you see 300/100 quoted anywhere?

I'm aware of the VOS2 = 300/150, VOS3 = 200/100 conditions.

@TDK   Do you see a specific note that the M4 has to run at half-speed? AHB4 can be DIV1 as far as I can tell.

[Pavel A.]

> you know about the life time of the replicants ? 

Yeah, the life time of these poor folks was crippled deliberately. This was a parody to the popular conspiracy theory of these times, that makers of electric bulbs deliberately cripple the life time of their products. Hope this is not the case with ST ))

[AScha.3]

@Tesla DeLorean , 

Just from first post:

100 MHz limit now. Also on F4 clock.

I just seen... don't ask me why it is so.

[AScha.3]

@Pavel A. , your great.

We discovered the conspiracy of the CPU manufacturers about the planned life time.

But we are in danger now - right?

[Tesla DeLorean]

@AScha.3 I feel I'm going in circles. This is APB4, the M4 clocks from AHB4

On the V-Step devices, I could swear this should be 120 MHz for APB4, but the Data Sheet, Reference Manual and Website are a complete dog's breakfast of internally inconsistent information.

I'm also looking for some reason why the M7/M4 can't be clocked at the same speed for anything less-than-equal to 240 MHz, I haven't seen any stated reason why AHB4 can't be DIV1

[STOne-32]

Hi @AScha.3 @Pavel A. ,

This is  not new in the industrial applications where we push the product to full operating mode and at High temperatures. In recent years we are seeing many new design for solar applications to become more and more digital as exemple, so using our T3 profile becomes a mandatory choice for such devices.  And by the way, all of semiconductor manufacturers are providing similar applications notes and optimization techniques here is one example  https://www.ti.com/lit/an/sprabx4b/sprabx4b.pdf

Cheers,

STOne-32

[Pavel A.]

Whatever it's worth - the full Cube clock tree picture for both CPUs, with max. values everywhere. All arrows without a divisor box are not configurable (1:1). Yes, Cube is not documentation, the manuals prevail...

@STOne-32 May your products be used only for solar and other peaceful things, and clear sky shine on the batteries.

[Tesla DeLorean]

I think the app note and related post should call this Electro-Migration, as that's what everyone else refers to this as.

[SofLit]

Hello,

I didn't read the overall discussion here (3 pages!) but what I wanted to mention is that even with industrial temp range devices (xxx3) you can use VOS0 @480MHz provided that TJmax=105°C for VOS0 and  TJmax=125°C for VOS1 as stated by the note:

May be you need to select the STM32H755xxx6 in CubeMx to workaround this but in final you need to respect the temperature ranges ..