[flight control development foundation tutorial 6] crazy shell · open source formation UAV SPI (six axis sensor data acquisition)

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SPI（ Six axis sensor data acquisition ）
    
    

    
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    One 、ICM20602 brief introduction
    Six axis sensors are widely used in today's smart wear and positioning and navigation products , The best six axis sensor is InvenSense The company's products ,ICM20602 It is one of its excellent six axis sensors .
    ICM20602 Integrate 3 Axis accelerometers and 3 Axis gyroscope , The range of gyroscope can be selected
    +/-250dps,+/-500dps,+/-1000dps and +/-2000dps These four , The range of accelerometer can be selected +/-2g,+/-4g,+/-8g and +/-16g Four kinds of .
    ICM20602 Support as much as 400KHz Of I2C And up to 10MHz Of SPI, It has high interface compatibility .
    ICM20602 The physical drawing of is shown below .
    
    
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    ICM20602 The pins are shown in the figure below .
    
    
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    Two 、SPI summary
    SPI Refer to Serial Peripheral Interface Abbreviation , Serial peripheral interface , It's a high speed 、 full duplex 、 Synchronous communication bus , And only four wires are used on the chip pins , The pins of the chip are saved ,SPI Of 4 The communication line is ：
    （1）MISO Master in slave out interface ;
    （2）MOSI Master out slave in interface ;
    （3）SCLK Clock signal generated by the master device ;
    （4）CS The slave device chip selection signal controlled by the master device .
    STM32F103 Of SPI Your clock can reach up to 18MHz, Support DMA.SPI Master slave communication , As shown in the figure below ：
    
    
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    When there are multiple devices attached to SPI On the bus , The wiring diagram is shown in the figure below .
    
    
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    Between single chip microcomputer and peripheral devices SPI Synchronous serial data transmission , Under the shift pulse of the main device , Data is transmitted bit by bit , Little Endian , High position behind , For full duplex communication , The speed of data transmission is generally faster than I2C The bus should be fast , What's the speed Mbp, Compared with other buses ,SPI Simple protocol , The relative data rate is high , however SPI It also has its disadvantages , For example, there is no specified flow control , There is no reply mechanism to confirm whether data has been received .
    
    3、 ... and 、SPI bus protocol
    SPI Communication requires the following knowledge ： Clock polarity 、 Clock phase and SPI The transmission timing of .
    
    （1） Clock polarity ,SPI By clock polarity （CPOL） To decide when the bus is idle , Synchronous clock （SCLK） Is the level of the signal line high or low . At that time, the polarity of the clock was 0 when （CPOL=0）, SCLK The signal line is low when idle ; At that time, the polarity of the clock was 1 when （CPOL=1）,SCLK The signal line is high when idle ;
    （2） Clock phase ,SPI Through the clock phase （CPHA） Used to decide when to sample the signal . At that time, the phase of the clock is 1 when （CPHA=1）, stay SCK The second jump edge of the signal line is sampled ; Whether the jump edge here is a rising edge or a falling edge ？ It depends on the polarity of the clock . At that time, the polarity of the clock was 0
    when , Take the falling edge ; At that time, the polarity of the clock was 1 when , Take the rising edge ; As shown in the figure below ：

 

 

chart 6
    At that time, the phase of the clock is 0 when （CPHA=0）, stay SCK Sample the first jump edge of the signal line . Jump edge is also related to clock polarity ： At that time, the polarity of the clock was 0 when , Take the rising edge ; At that time, the polarity of the clock was 1
    when , Take the falling edge ; As shown in the figure below ：
    
    
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    Four 、 SPI register
    What is used in this experiment is STM32 The hardware SPI,STM32 The hardware SPI There are many registers involved , Here we choose the more important ones to explain .
    
    （1）SPI_CR1：SPI Control register 1, As shown in the figure below ：
    
    
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    among SPE by SPI Enable control bit , be equal to 1 Time enabled SPI, be equal to 0 Turn off SPI;BR[2:0] by SPI Baud rate control bit ,BR[2:0] be equal to 000 Then the baud rate is fPCLK/2, be equal to 001 Then the baud rate is fPCLK/4, be equal to 010 Then the baud rate is fPCLK/8, be equal to 011 Then the baud rate is fPCLK/16, be equal to 100 Then the baud rate is fPCLK/32, be equal to 101 Then the baud rate is fPCLK/64, be equal to 110 Then the baud rate is fPCLK/128, be equal to 111 Then the baud rate is fPCLK/256;MSTR by SPI Master slave mode selection bit , be equal to 0 When in slave mode , be equal to 1 Time based mode ;CPOL by SPI Clock polarity setting bit , by 0 Then the idle clock is low , by 1 Then the idle clock is high ;CPHA by SPI Clock phase setting bit , be equal to 0 when , Start collecting at the edge of the first clock jump , be equal to 1 when , In the 2 The edge of the clock jumps and starts to collect .
    （2）SPI_SR：SPI Status register , As shown in the figure below ：
    
    
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    among TXE Is the send buffer status bit , This bit is 0 The send buffer is not empty , by 1 The send buffer is empty ;RXNE Is the receive buffer status bit , This bit is 0 The receive buffer is empty , This bit is 1 when , The receive buffer is not empty .
    （3）SPI_DR：SPI Data register , Used to store received or sent data .SPI_DR The description of is shown in the figure below ：
    
    
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    among DR[15:0] Deposit SPI data .
    5、 ... and 、 Six axis sensor data acquisition experiment
    
    Six axis sensor data acquisition experiment use STM32 The hardware SPI With six axis sensor ICM20602 Connect , A serial port 1 namely UART1, adopt USB Connect the serial port module to the computer , hold SPI The obtained six axis data passes through the serial port 1 The serial port debugging assistant transmitted to the computer is displayed . When doing this experiment, you need to temporarily remove the visual module , And the USB The line to serial port is connected to the interface of the visual module . Six axis sensors ICM20602 White on top of the drone RGB In the lantern box , Through the soft row handle SPI And power supply outlet , As shown in the figure below .
    
    
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    According to the schematic diagram , You can see ICM20602 Of course SPI The interfaces are ：PB13、PA5、PA6、PA7, As shown in the figure below .
    
    
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    A serial port 1 The configuration of can refer to 《 A serial port （ Basic transceiver ）, Configuration code （ By calling the official library ） obtain ICM20602 The idea of data code writing is as follows ：
    
    Code thinking
    
    
    surface 1
    SPI The initialization code is as follows ：
    
    
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    SPI The reading and writing code of is as follows .
    
    
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    ICM20602 The initialization code of is as follows .
    
    
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    ICM20602 The reading and writing code of is as follows .
    
    
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    Pay attention to configuring the serial port for sending , In this way, the data can be sent to the computer . A serial port 1 adopt USB Connect the serial port module to the computer , obtain ICM20602 The code is as follows .
    
    
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    preservation 、 compile 、 Download code , You can see USB The serial port module is constantly printing ICM20602
    Of X High axial acceleration 8 position , The data is shown in the figure below ：
    
    
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