1. Gossip

When developing recently, I used the STM32F030F4P6 microcontroller, which has only 20 pins and is very cheap, but it has complete functions; timers, external interrupts, serial ports, IIC, SPI, DMA and WWDG, etc., are all available, making it very suitable for small devices. But there is a problem, it is Cortex-M0 core, unlike M3 and M4 cores, it can support bit-band operation (that is, one bit operation, like 80C51 microcontroller), which brings a little trouble to program transplantation or development, so I use the bit segment operation of C language structure to realize the bit-band operation, but the efficiency may be slightly inferior to the real bit-band operation, but the code is compatible and can be applied to basically any processor. I hope it can help you. The original address of this article: http://www.cnblogs.com/endlesscoding/p/7429743.html, please indicate the source for reprinting.

2. Basic knowledge of bit band operation

 There are a lot of information about the real bit-band operation on the Internet, and they are written in great detail. Here I will just briefly talk about my understanding. In addition, if you do not understand the real bit-band operation, it will not affect your understanding of this article, because this article has nothing to do with the bit-band operation. It is just an imitation and should not be taken seriously. If you do not want to understand the real bit-band operation, you can directly ignore this section.

If we do not use bit-banding operations, we have to move 32 bits (STM32 is 32 bits) when we operate a piece of data. To make an inappropriate analogy, this is equivalent to sitting on a train with 32 carriages, but the train has only one door. If we want to check the information of the passengers in the train, or if the passengers want to get off, they must enter and exit from that door, as shown in Figure 1.

Figure 1 A 32-car train with only one door

 If we have bit-band operation, it is equivalent to installing 32 doors on this 32-carriage train. In this way, if you want to check the information of a passenger or get off the train, you can quickly get off from the designated door. As shown in Figure 2 below.

Figure 2 A 32-car train with 32 doors

With 32 gates, the speed is much faster, but the hardware cost will definitely increase. This is why the STM32F030 series does not have bit-banding operations, because its cost is low.

3. C language structure and body segment operation

This section mainly describes the basic knowledge of C language structures. If you are an expert in C language, please ignore this section. In C language, there is a bit field in the declaration of a structure, which can control how many bits the members in this structure occupy. Regarding its use, there is the following code:

 1 typedef struct _16_Bits_Struct

 2 {

 3 u16 bit0 : 1; // occupies one byte

 4     u16 bit1 : 1;

 5 u16 bit2 : 1;

 6 u16 bit3 : 1;

 7 u16 bit4 : 1;

 8 u16 bit5 : 1;

 9 u16 bit6 : 1;

10     u16 bit7 : 1;

11 u16 bit8 : 1;

12 u16 bit9 : 1;

13 u16 bit10 : 1;

14 u16 bit11 : 2; // occupies two bytes

15 u16 bit12 : 3; // occupies three bytes

16 } _16_Bits_Struct;

The _16_Bits_Struct structure type above occupies 2 bytes, or 16 bits, but the number of bits occupied by its 13 member variables is not all the same. The number after the ":" determines how many bits it occupies. The code is as follows, which operates a bit of this structure type.

 1     _16_Bits_Struct _16_bits;

 2     unsigned short _16bits_data;

 3 memset(&_16_bits, 0, sizeof(_16_Bits_Struct)); // clear its memory to 0

 4 

 5     _16_bits.bit2 = 1;

 6     _16_bits.bit5 = 1;

 7     _16_bits.bit8 = 5;

 8 

 9     _16bits_data = *((unsigned short*)(&_16_bits));

10 

11     printf("_16bits_data = %0xH\n", _16bits_data);

The output is:

From the result, we can see that in the structure, bit0~bit12 are from low to high. In line 7 of the above code, although 5 is written to bit8, because it only occupies one bit, only the lowest bit of 5(D)=0101(B) is taken, which is 1. Therefore, the final result is 124H, and its memory structure is shown in Figure 3 below.

Figure 3 Structure memory structure diagram 

4. STM32F030 emulation operation

With the foundation of the above structure bit segment operation, it is very close to realize the bit band operation of STM32F030. I plan to make a simple one to realize the operation of a certain GPIO pin to achieve the function of turning on and off the LED.

From the reference manual of STM32F030, find the GPIO output register ODR and see its basic information as shown in Figure 4. This register is readable and writable (RW), so as long as we write 1 to one of the bits in this register, the pin will output 1, and write 0 to output 0 (of course, the prerequisite is that you configure it to output mode and enable its clock).

Figure 4 GPIO ODR register structure diagram

How do I operate this register one bit at a time? Let's look at the code below to explain.

 1 typedef struct _16_Bits_Struct

 2 {

 3 u16 bit0 : 1;

 4     u16 bit1 : 1;

 5 u16 bit2 : 1;

 6 u16 bit3 : 1;

 7 u16 bit4 : 1;

 8 u16 bit5 : 1;

 9 u16 bit6 : 1;

10     u16 bit7 : 1;

11 u16 bit8 : 1;

12 u16 bit9 : 1;

13 u16 bit10 : 1;

14 u16 bit11 : 1;

15     u16 bit12 : 1;

16 u16 bit13 : 1;

17     u16 bit14 : 1;

18     u16 bit15 : 1;

19 } Bits_16_TypeDef;

20 #define LED_GPIO_CLK   RCC_AHBPeriph_GPIOA 

21 #define LED_PORT       GPIOA

22 #define LED_PIN        GPIO_Pin_4

23 //Use the bit segment operation of the structure, compatible with the bit band operation of Cortex-M3.

24 #define LED_PORT_OUT    ((Bits_16_TypeDef *)(&(LED_PORT->ODR)))

25 #define LED             (LED_PORT_OUT->bit4) 

My hardware connection is: LED is connected to pin 4 of GPIOA. Lines 1 to 19 have been explained in the previous structure knowledge. Lines 20 to 22 are just some macro definitions for better code porting, which are unnecessary. Line 24 is more critical: first take out the address of GPIOA->ODR, and then force it to be converted to Bits_16_TypeDef * type (note, it is a pointer type). After converting to this type, ODR has the characteristics of a bit field, so it can be operated on. Line 25 defines the LED connected to PA.4 as the 4th bit of GPIOA->ODR.

With this operation, it is easy to turn our LED on and off. The code is as follows.

1 LED = 0;//LED亮

2 LED = 1;//LED is off

Due to different hardware connections, the effect may be the opposite. After reading this, do you think the operation is very simple?

The complete code is as follows:

 1 /*------------------------------------------------------------------------------

 2 Fan Monitoring System (August 12, 2017 12:22:38)

 3 Functional description:

 4 LED switch function, mainly used for status display

 5 

 6 Resources used: GPIOA changes as the board is not used

 7 

 8 File Description: None

 9 Author: Endless Email: endless@139.com Time: August 10, 2017 21:35:38

10 Modification: None Time:

11 ------------------------------------------------------------------------------*/

12 #include "led.h"

13 #include "stm32f0xx.h"

14 

15 /*-----------------------------------------------------------------------------

16 Function: LED initialization

17 Function parameters: None

18 Function returns: None

19 Function Description: Before calling this function, you need to modify the macro definition of LED pin in LED.h

20 Author: Endless    

21 -----------------------------------------------------------------------------*/

22 void LED_Init(void)

23 {

24     GPIO_InitTypeDef GPIO_InitStructure;

25 

26     RCC_AHBPeriphClockCmd(LED_GPIO_CLK, ENABLE);

27 

28     GPIO_InitStructure.GPIO_Pin = LED_PIN;

29     GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;

30     GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;

31     GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;    

32     GPIO_Init(LED_PORT, &GPIO_InitStructure);

33 }

led.c

 1 #ifndef __led_H

 2 #define __led_H 

 3 

 4 #include "stm32f0xx.h"

 5 #include "mytype.h"

 6 

 7 #define LED_GPIO_CLK   RCC_AHBPeriph_GPIOA 

 8 #define LED_PORT          GPIOA

 9 #define LED_PIN        GPIO_Pin_4

10 

11 //Use the bit segment operation of the structure, compatible with the bit band operation of Cortex-M3.

12 #define LED_PORT_OUT    ((Bits_16_TypeDef *)(&(LED_PORT->ODR)))

13 #define LED               (LED_PORT_OUT->bit4)    

14 

15 void LED_Init(void);

16 

17 #endif

led.h

 1 #ifndef  __MYTYPE_H

 2 #define  __MYTYPE_H

 3 #include "stm32f0xx.h"

 4 

 5 #ifndef BIT

 6 #define BIT(x)    (1 << (x))

 7 #endif

 8 

 9 #ifndef u8

10 #define u8 uint8_t

11 #endif

12 

13 #ifndef u16

14 #define u16 uint16_t

15 #endif

16 

17 #ifndef u32

18 #define u32 uint32_t

19 #endif

20 

21 #ifndef NULL

22 #define NULL 0

23 #endif

24 

25 /*------------------------------------------------------------------------------

26 User defined variables

27 Function description: Use the bit segment operation of the structure to realize bit operation

28 Author: Endless 2017-08-13 18:32:37

29 Modification: None Time:

30 ------------------------------------------------------------------------------*/

31 typedef struct _16_Bits_Struct

32 {

33 u16 bit0 : 1;

34     u16 bit1 : 1;

35 u16 bit2 : 1;

36 u16 bit3 : 1;

37 u16 bit4 : 1;

38 u16 bit5 : 1;

39 u16 bit6 : 1;

40     u16 bit7 : 1;

41 u16 bit8 : 1;

42 u16 bit9 : 1;

43 u16 bit10 : 1;

44 u16 bit11 : 1;

45     u16 bit12 : 1;

46 u16 bit13 : 1;

47     u16 bit14 : 1;

48     u16 bit15 : 1;

49 } Bits_16_TypeDef;

mytype.h

If you want to perform more bit operations, just define it a few more times, it's very easy. That's almost the end. I hope it can help you. If you have any questions, please contact me or leave a message below.

Summarize

It is not easy to do technology, I hope we can all stick to it together!!