How does the STM32 Bootloader know the frequency of the crystal you soldered? How does it make the judgment?

fxyc87

How does the STM32 Bootloader know the frequency of the crystal you soldered? How does it make the judgment? [Copy link]

 

Many STM32 chips have USB upgrade function, so how does the Bootloader know how many M crystal oscillators you have soldered?

Then the USB frequency happens to be multiplied to 48M?

Most STM32s require an external crystal oscillator to use the USB function, and only a few support crystal-free USB function.

Is it determined by the USB sof signal or the built-in RC clock?

I think I used 8M and 12M before, no problem.

I write my own program and I know my own crystal oscillator, but how does the bootloader detect it?

wangerxian

The bootloader should use the internal high-speed crystal oscillator.

fxyc87

wangerxian posted on 2024-2-22 09:12 The bootloader should use the internal high-speed crystal oscillator.

When using USB for DFU upgrade, you must use an external crystal oscillator. For example, the STM32H7 manual says that it does not support running USB without a crystal oscillator. Similarly, the STM32F072 supports USB functions without a crystal oscillator.

So your statement is not valid.

The DFU I'm talking about is the DFU function that comes with the bootloader, not the DFU of the user program.

wangerxian

fxyc87 posted on 2024-2-22 09:14 When using USB for DFU upgrade, you must use an external crystal oscillator. For example, the STM32H7 manual says that it does not support running USB without a crystal oscillator. There are similar ST ...

Then I think we can test whether the manufacturer's bootloader's DFU can run without connecting the external crystal oscillator.

damiaa

I feel:

The manufacturer's bootloader knows the crystal oscillator inside. Because this is fixed, it can be configured with a value to reach 48M.

It can start the internal crystal oscillator first to measure the external crystal oscillator, whether it can be started, what the frequency is, and whether it is stable. If there is no external crystal oscillator, it will continue to use the internal crystal oscillator to run. In fact, the CPU starts using the internal crystal oscillator. If an external crystal oscillator is to be used, it will wait until the external crystal oscillator is stable before switching to it.

秦天qintian0303

What is the basis for the bootloader process? For ARM such as STM32, it should be the startup file (startup....s), which contains SystemInit, which has been initialized. You can change it or reconfigure it after entering the main program

fxyc87

Qintianqintian0303 posted on 2024-2-22 10:38 What is the basis for the bootloader process? For ARM such as STM32, it should be the startup file (startup....s), which contains Syst ...

I mean the bootloader that comes with the MCU, not the user program

It is provided by the chip when it leaves the factory. For example, some STM32 chips can use the serial port or USB to upgrade the program when boot0 is pulled low.

In this mode, how does it know the frequency of the external crystal oscillator soldered?

wsmysyn

I am not sure how it is implemented. I guess there may be internal counting. The RC has been calibrated at the factory. Although the accuracy is low, 1-2% should be achievable.

Our chips start the BootLoader from the internal RC by default, and then switch to the high-frequency clock. From this, we can guess that our chips do not automatically identify the crystal frequency. The default is whatever it is, and the user cannot choose it.

秦天qintian0303

fxyc87 posted on 2024-2-22 11:01 I mean the bootloader that comes with the MCU, not the user program that comes with the chip when it leaves the factory. For example, some STM32 chips, when boot0 is pulled low, you can...

SystemInit is in the factory startup file. It usually starts with the internal clock, and then configures the external clock data. There are external clock parameters in the startup file. We also need to change this when changing the external clock.

Ejack1979

According to STMicroelectronics' AN3156, the USB part in the bootloader uniformly uses the DFU protocol, and the processing of the USB clock source is different: one type of chip directly uses HSI to multiply the frequency to 48MHz and then allocates it to the USB module; another type of chip first runs with HSI and establishes a connection with the USB Host, then tries to use different external clock configurations to multiply the frequency and allocate it to the USB module, and tests whether it can successfully send and receive messages. If it fails, try the next set of configurations...

As for which chips execute according to which configuration, see AN2606.

In summary, the Bootloader does not know the frequency of the external crystal oscillator, and either uses HSI to run the USB interface or repeatedly tries USB communication according to several specific sets of frequencies (8MHz, 14.7456MHz, 25MHz).

fxyc87

Ejack1979 posted on 2024-2-22 15:07 According to STMicroelectronics' AN3156, the USB part in the bootloader uniformly adopts the DFU protocol, and the processing of the USB clock source is different: a type of chip directly...

Thanks for clarifying this, this is the correct answer.

fxyc87

Qintianqintian0303 posted on 2024-2-22 11:59 SystemInit is in the factory startup file. It is usually started with the internal clock, and then the external clock data is configured. There is an external clock in the startup file...

The answer on the 10th floor is correct.

SystemInit is a user program. Not the MCU's bootloader.

The bootloader that comes with the MCU is not open.

fxyc87

wsmysyn posted on 2024-2-22 11:25 It is not clear how it is implemented. I guess there may be a counter inside. The RC has been calibrated at the factory. Although the accuracy is low, 1-2% should be...

If USB is not used, the bootloader can ignore the external crystal and use the internal RC

However, if USB is used, the internal RC accuracy will not be sufficient, which will cause external USB communication to fail.

The answer on the 10th floor should be correct.

秦天qintian0303

fxyc87 posted on 2024-2-22 16:06 The answer on the 10th floor is correct. SystemInit is a user program. It is not the MCU's bootloader. The MCU's own bootloader is not open.

Oh, then we probably haven't touched on it very deeply. This startup file is also provided by the manufacturer.

wsmysyn

fxyc87 posted on 2024-2-22 16:07 If USB is not used, the bootloader can ignore the external crystal oscillator and use the internal RC. But if USB is used, the internal RC accuracy is not enough, which will cause external...

For most peripherals, the RC accuracy is definitely not enough. Generally, the BootLoader starts with the RC clock, configures the PLL after startup, and then switches to the PLL clock. If there is any,

wangerxian

I'm not sure how it's implemented specifically. My guess is that there may be a counter inside, and the RC has been calibrated at the factory. Although the accuracy is low, 1-2% should be about right. Our chips start the BootLoader from the internal RC by default, and then switch to the high-frequency clock. Based on this, I guess that our chip does not automatically identify the crystal frequency. The default is whatever it is, and the user cannot choose.

Are you a chip developer?

wsmysyn

wangerxian posted on 2024-2-22 19:38 Are you engaged in chip development?

No, I do chip testing. I just know more about the internal design of the chip than ordinary users. Some test modes are not open to users. I communicate more with design colleagues.

wangerxian

wangerxian posted on 2024-2-22 19:38 Are you a chip developer?

No, I do chip testing. I just know more about the internal design of the chip than ordinary users. Some test modes are not open to users. I communicate more with design colleagues

Which domestic chip factory are you from? []

wsmysyn

wangerxian posted on 2024-2-22 19:54 No, I do chip testing. I just know more about the internal design of the chip than ordinary users. Some test modes are not open to users, and...

Qingwei, a team from the Institute of Microelectronics at Tsinghua University

It’s not the general market, but some specific scenarios, such as smart door locks, smart cameras, and cloud-based AI chips.

wangerxian

wsmysyn posted on 2024-2-22 20:00 Qingwei, the team from Tsinghua University Microelectronics Institute is not a general market, some specific scenarios, smart door locks, smart cameras, and cloud push...

Is there an official website? Let’s take a look at your chips.