STM32G474: Performance issues (?) and freq() issues.

[nspsck]

I recently recieved my STM32G474CE boards made by WeAct Studio and started testing Micropython on it. Soon I have noticed that the freq() function does not work as expected and the performance from this thing is way worse than the F4 series.

Here are some results in the REPL using the freq() function:

>>> pyb.freq()
(170000000, 170000000, 42500000, 85000000) # 170MHz
>>> pyb.freq(96000000) # 96MHz
>>> pyb.freq()
(8000000, 8000000, 2000000, 4000000) # 8MHz
>>> pyb.freq(170000000) # 170MHz
>>> pyb.freq()
(16400000, 16400000, 4100000, 8200000) # 16.4MHz

It seems like the the clock is divided by 10 for some reasons. Also, according to the datasheet in the section about pll characteristics, it seems the MCU needs different voltage for different clock frequencies which I do not see covered anywhere in the powerctl.c. (This section.) Am not so sure if that would cause any problems.

I have also tried to modify the pllvalues.py by adding a component to the mcu_table list declared in line 34:

    "stm32g4": MCU(
        range_sysclk=range(2, 170 + 1),
        range_m=range(1, 8 + 1), # Can go 16, but in the Manual it changes PLLM to PLLSYSM
        range_n=range(8, 127 + 1),
        range_p=range(2, 31 + 1),
        range_q=range(2, 8 + 1, 2),
        range_vco_in=range(3, 16 + 1), # 2.66 - 16
        range_vco_out=range(96, 344 + 1),
    ),

But this results to a Fatal error: can't change freq. Could this also just be my chip?

For the performance part, I have used 2 simple tests:

import time

# Int
def test(p):
    r = range(p)
    c = 0
    for i in r:
        c += 1
    return c

# Float
# def test(p):
#     r = range(p)
#     c = 0.0001
#     for i in r:
#         c += c
#         c = c / 2
#     return c * 4 / p

def main():
    ms = time.ticks_ms
    diff = time.ticks_diff
    
    while True:
        s = ms()
        print(test(50000))
        d = diff(ms(), s)
        print("Time used %dms" % d)
        
main()

Here are some results running my "benchmark":

# STM32G474CE @170MHz
# Float
MPY: sync filesystems
MPY: soft reboot
8e-09
Time used 1074ms
8e-09
Time used 1076ms
8e-09
Time used 1076ms
# Int
MPY: sync filesystems
MPY: soft reboot
50000
Time used 292ms
50000
Time used 292ms
50000
Time used 293ms
50000

# STM32F411CE @120MHz
# Float
MPY: sync filesystems
MPY: soft reboot
8e-09
Time used 795ms
8e-09
Time used 796ms
8e-09
Time used 797ms
# Int
MPY: sync filesystems
MPY: soft reboot
50000
Time used 167ms
50000
Time used 167ms
50000
Time used 167ms
50000

The results is really odd for me, since at least the Integer operation should not differ that much...

Any help and suggestions are greatly appreciated!

[ajt2018]

Could it be related to the fact that the WeAct board costs £0.40 from AliExpress yet the STM32G431CBU6 on it's own would set you back £2.6 if you bought 1000's of them from digikey ?

[davefes]

@nspsck, I need a STM32 with more GPIO than the STM32F411. Did you manage to get this variant working properly?

[nspsck]

@davefes hi, sadly not. But have a look at: https://de.aliexpress.com/item/1005006051651136.html?spm=a2g0n.productlist.0.0.2eff31fffELZ4A&browser_id=bbdc4688ff7e4fa6ba7bf004319ef9fb&aff_platform=msite&m_page_id=hhdhvrtgcablurld192fc38c48c11080024e5781a3&gclid=&pdp_npi=4%40dis%21CHF%214.77%211.54%21%21%2138.47%2112.39%21%40211b80e117308084317374384efa9b%2112000035503740772%21sea%21CH%210%21ABX&algo_pvid=ce2ee2ab-73ee-4872-9918-e73c750397c9

The F412RET6. Double the RAM, almost same price, but you can not solder a spi flash directly on the board.

[davefes]

Downloaded the datasheet, looking at the package and trying to count the pins in the ad I'd guess it is a LQFP64 package. That is 50 GPIO.

I would like 80 GPIO.

Would the STM32G474CE board from WeACT work OK for GPIO? I want to control 25 stepper motor controller boards, so only GPIO toggling is required.

Thanks.

[nspsck]

That C in STM32G474CE means that this soc has 48 pins.

C - 48 pins
R - 64 pins
V - 100 pins
Z - 144 pins

You might want something like a STM32F407VE or STM32F407VG

B - 128KB flash
E - 512KB flash
G - 1MB flash

Or the STM32H723ZG/VG, STM32H743VG. STM32H750VB if you know how to get the qspi flash working.

[davefes]

Thanks for the clarification. I had considered the STM32H723VGT6 from WeAct. The actual program size is relatively small, so if on-board flash works then I might be OK.
https://micropython.org/download/NUCLEO_H723ZG/

1MB of flash, which is good enough for me.