Electronic – how can a GPIO of stm32 have many alternative functions

gpiostm32

I am working on the assignments of pins of STM32F103ZET¹.

On page 31 of datasheet, it says that PA0 has many alternative functions: TIM2_CH1_ETR \ USART2_CTS \ WKUP \ ADC123_IN0 \ TIM5_CH1 \ TIM8_ETR. From the reference manual, I know that TIM2_CH1_ETR and USART2_CTS can be remapped.

What about other functions? What if I want to use TIM5_CH1 and TIM8_ETR at the same time? How can the STM32 know whether I want to consider PA0 as TIM5_CH1 or TIM8_ETR?

^{1: datasheet, reference manual}

Best Answer

After spending a few minutes searching the datasheet, I've concluded that you can't remap those functions. However, they're both inputs. So you can use them both at once to trigger different things in those two timers.

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Electronic – Set STM32 GPIO clock and data pins as fast as possible

I answered to your related question why you could only toggle at 4 MHz when you expected 100 MHz:

If the 4 MHz is about 4 MHz, and not exactly 100 MHz/25 then the problem is probably with the C function GPIO_WriteBit.

For high speed operations and operations which require accurate timing you better code in assembly than in C. If you look at the assembly code created by GPIO_WriteBit it may be half a page long, depending on what kind of features the function has, and how much the compiler's optimizer can do with it.

You don't say which development toolchain you're using, but many/most C compilers can handle in-line assembly.

So, write the functions in assembly. A function like

 GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;

should take no more than 2 instructions in assembly, while the compiled C code may take 20 times as much. Or more.

Electronic – How to realise bidirectional ports in FSMC function of STM32

Have a look at Section 9.1.4 on page 157:

9.1.4 Alternate functions (AF)

It is necessary to program the Port Bit Configuration Register before using a default alternate function.

For alternate function inputs, the port must be configured in Input mode (floating, pullup or pull-down) and the input pin must be driven externally.

Note: It is also possible to emulate the AFI input pin by software by programming the GPIO controller. In this case, the port should be configured in Alternate Function Output mode. And obviously, the corresponding port should not be driven externally as it will be driven by the software using the GPIO controller.

For alternate function outputs, the port must be configured in Alternate Function Output mode (Push-Pull or Open-Drain).

For bidirectional Alternate Functions, the port bit must be configured in Alternate Function Output mode (Push-Pull or Open-Drain). In this case the input driver is configured in input floating mode

If you configure a port bit as Alternate Function Output, this disconnects the output register and connects the pin to the output signal of an on-chip peripheral.

If software configures a GPIO pin as Alternate Function Output, but peripheral is not activated, its output is not specified.

If a pin or a bus is supposed to be bidirectional for an Alternate Function, configure it as an Alternate Function in Output mode and the input configuration happens automatically.

If the pin is supposed to be an input for an Alternate Function, configure it in Input Mode.

If the pin is supposed to be an output for an Alternate Function, configure it in Output mode.

When you're using a pin as GPIO, you have to choose between Input mode or Output mode.

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Electronic – Set STM32 GPIO clock and data pins as fast as possible

Electronic – How to realise bidirectional ports in FSMC function of STM32

9.1.4 Alternate functions (AF)

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