Some problem with Rcc config

[schrodinger1772]

Hi,

When I want to config the clock for the system, I meet some problem. I used the stm32f401rct6 and the code was like let clock = rcc.cfgr
.use_hse(8.MHz())
.sysclk(84.MHz())
.hclk(84.MHz())
.pclk1(42.MHz())
.pclk2(84.MHz())
.freeze();
I copy that from the example, but that doesnot work when I use the usart1. But if I comment the sysclk, it can work but it's sysclk is 8MHZ.

If you know why that happen, I will appreciate that so much. Thanks for your time.

shvshy

[burrbull]

First of all I'd check the oscillator on your board. Try to comment out .use_hse(8.MHz()) instead. Also there is usually 16 or 25 MHz external oscillators on F4 boards, not an 8 MHz.

[schrodinger1772]

Thanks a lot for your time. Here's the pic of the oscillator.

that's actually 8Mhz and I comment out the use_hse. there's nothing out from the usart1. Thanks again for you reply.

shevshy

[burrbull]

Is it freezes or it works but usart not working?
If freezes, try to find a place where it's happen. For example using defmt::println.

[schrodinger1772]

Hi, that is kind of embarassing, I tick the run button on the vs of the defmt part, it works well, that's really useful. just forget my last reply, I am such a idiot. Thanks again. have a good day, I will try to find out if it freezed.

shevshy

[schrodinger1772]

Hi, master.

Ohhh, that's really coventient using defmt, e, I found that clock has been freezed. and the problem maybe happened in let mut delay = dp.TIM1.delay_ms(&clock);that line. and I will give the error followd ERROR panicked at C:\Users\schroadinger.cargo\registry\src\index.crates.io-6f17d22bba15001f\stm32f4xx-hal-0.22.0\src\timer.rs:780:55:
called Result::unwrap() on an Err value: TryFromIntError(())
└─ panic_probe::print_defmt::print @ C:\Users\schroadinger.cargo\registry\src\index.crates.io-6f17d22bba15001f\panic-probe-0.3.2\src\lib.rs:104
Frame 0: syscall1 @ 0x08001fae inline
C:\Users\schroadinger.cargo\registry\src\index.crates.io-6f17d22bba15001f\cortex-m-semihosting-0.5.0\src/lib.rs:201:13
Frame 1: report_exception @ 0x0000000008001fac inline
C:\Users\schroadinger.cargo\registry\src\index.crates.io-6f17d22bba15001f\cortex-m-semihosting-0.5.0\src/macros.rs:28:9Frame 2: exit @ 0x0000000008001fac
C:\Users\schroadinger.cargo\registry\src\index.crates.io-6f17d22bba15001f\cortex-m-semihosting-0.5.0\src/debug.rs:73:25Frame 3: _cortex_m_rt_HardFault @ 0x08000834
E:\Rust_32\my-app\src/lib.rs:36:9
Frame 4: HardFault @ 0x08003670
C:\Users\schroadinger.cargo\registry\src\index.crates.io-6f17d22bba15001f\cortex-m-rt-0.7.3\src/lib.rs:1046:5
Error: Semihosting indicates exit with reason: 0x20023

Stack backtrace:
0:
1:
2: hid_write
3:
4:
5:
6:
7:
8:
9:
10: hid_write
11: BaseThreadInitThunk
12: RtlUserThreadStart

when I changed the delay_ms as delay_us. everything goes well. So, what the problem of that. Thanks a lot for your all helping, that help me a lot.

shevshy

[burrbull]

There is a note in docs: https://docs.rs/stm32f4xx-hal/latest/stm32f4xx_hal/timer/delay/type.DelayMs.html

[burrbull]

when I changed the delay_ms as delay_us. everything goes well. So, what the problem of that. Thanks a lot for your all helping, that help me a lot.

delay_ms() is just an alias for delay::<1000>() where 1000 is frequency of timer clocking used to calculate timer prescaler which is 16bit width.
84MHz / 1kHz == 85000 > 2^16