Arduino - 一次管理两个SPI设备

时间:2013-03-08 23:13:21

标签: arduino microcontroller spi

我正在尝试使用相同的MISO,MOSI和CLOCK引脚同时控制两个SPI设备,但不同的SS引脚。

一个是来自Wiflyshield SparkFun使用SPI到UART芯片,另一个是MAX31855

他们独立工作,但不能一起工作..

我正在使用的SPI-to-UART代码如下所示。我所做的唯一更改是在头文件中;我将select()deselect()设置为公开。

#include "SpiUart.h"

// See section 8.10 of the datasheet for definitions
// of bits in the Enhanced Features Register (EFR)
#define EFR_ENABLE_CTS 1 << 7
#define EFR_ENABLE_RTS 1 << 6
#define EFR_ENABLE_ENHANCED_FUNCTIONS 1 << 4

// See section 8.4 of the datasheet for definitions
// of bits in the Line Control Register (LCR)
#define LCR_ENABLE_DIVISOR_LATCH 1 << 7

// The original crystal frequency used on the board (~12 MHz) didn't
// give a good range of baud rates so around July 2010 the crystal
// was replaced with a better frequency (~14 MHz).
#ifndef USE_14_MHZ_CRYSTAL
#define USE_14_MHZ_CRYSTAL true // true (14 MHz) , false (12 MHz)
#endif

#if USE_14_MHZ_CRYSTAL
#define XTAL_FREQUENCY 14745600UL // On-board crystal (New mid-2010 Version)
#else
#define XTAL_FREQUENCY 12288000UL // On-board crystal (Original Version)
#endif

// See datasheet section 7.8 for configuring the
// "Programmable baud rate generator"
#define PRESCALER 1 // Default prescaler after reset
#define BAUD_RATE_DIVISOR(baud) ((XTAL_FREQUENCY/PRESCALER)/(baud*16UL))

// TODO: Handle configuration better
// SC16IS750 register values
struct SPI_UART_cfg {
    char DataFormat;
    char Flow;
};

struct SPI_UART_cfg SPI_Uart_config = {
    0x03,
    // We need to enable flow control or we overflow buffers and
    // lose data when used with the WiFly. Note that flow control
    // needs to be enabled on the WiFly for this to work but it's
    // possible to do that with flow control enabled here but not there.
    // TODO: Make this able to be configured externally?
    EFR_ENABLE_CTS | EFR_ENABLE_RTS | EFR_ENABLE_ENHANCED_FUNCTIONS
};


void SpiUartDevice::begin(unsigned long baudrate) {
    /*
     * Initialize SPI and UART communications
     *
     * Uses BAUD_RATE_DEFAULT as baudrate if none is given
     */

    SPI.begin();
    initUart(baudrate);
}

void SpiUartDevice::deselect() {
    /*
     * Deslects the SPI device
     */

    digitalWrite(SS, HIGH);
}


void SpiUartDevice::select() {
    /*
     * Selects the SPI device
     */

    digitalWrite(SS, LOW);
}


void SpiUartDevice::initUart(unsigned long baudrate) {
    /*
     * Initialise the UART.
     *
     * If initialisation fails this method does not return.
     */

    // Initialise and test SC16IS750
    configureUart(baudrate);

    if(!uartConnected()){
        while(1) {
          // Lock up if we fail to initialise SPI UART bridge.
        };
    }

  // The SPI UART bridge is now successfully initialised.
}


void SpiUartDevice::setBaudRate(unsigned long baudrate) {
    unsigned long divisor = BAUD_RATE_DIVISOR(baudrate);

    writeRegister(LCR, LCR_ENABLE_DIVISOR_LATCH); // "Program baudrate"
    writeRegister(DLL, lowByte(divisor));
    writeRegister(DLM, highByte(divisor));
}


void SpiUartDevice::configureUart(unsigned long baudrate) {
    /*
     * Configure the settings of the UART.
     */

    // TODO: Improve with use of constants and calculations.
    setBaudRate(baudrate);

    writeRegister(LCR, 0xBF); // Access EFR register
    writeRegister(EFR, SPI_Uart_config.Flow); // Enable enhanced registers
    writeRegister(LCR, SPI_Uart_config.DataFormat); // 8 data bit, 1 stop bit, no parity
    writeRegister(FCR, 0x06); // Reset TXFIFO, reset RXFIFO, non FIFO mode
    writeRegister(FCR, 0x01); // Enable FIFO mode
}


boolean SpiUartDevice::uartConnected() {
    /*
     * Check that UART is connected and operational.
     */

    // Perform read/write test to check if the UART is working
    const char TEST_CHARACTER = 'H';

    writeRegister(SPR, TEST_CHARACTER);

    return (readRegister(SPR) == TEST_CHARACTER);
}


void SpiUartDevice::writeRegister(byte registerAddress, byte data) {
    /*
     * Write <data> byte to the SC16IS750 register <registerAddress>
     */

    select();
    SPI.transfer(registerAddress);
    SPI.transfer(data);
    deselect();
}


byte SpiUartDevice::readRegister(byte registerAddress) {
    /*
     * Read byte from SC16IS750 register at <registerAddress>.
     */

    // Used in SPI read operations to flush slave's shift register
    const byte SPI_DUMMY_BYTE = 0xFF;

    char result;

    select();
    SPI.transfer(SPI_READ_MODE_FLAG | registerAddress);
    result = SPI.transfer(SPI_DUMMY_BYTE);
    deselect();
    return result;
}


int SpiUartDevice::available() {
    /*
     * Get the number of bytes (characters) available for reading.
     *
     * This is data that's already arrived and stored in the receive
     * buffer (which holds 64 bytes).
     */

    // This alternative just checks if there's data but doesn't
    // return how many characters are in the buffer:
    //    readRegister(LSR) & 0x01
    return readRegister(RXLVL);
}


int SpiUartDevice::read() {
    /*
     * Read byte from UART.
     *
     * Returns byte read or or -1 if no data available.
     *
     * Acts in the same manner as 'Serial.read()'.
     */

    if (!available()) {
        return -1;
    }

    return readRegister(RHR);
}


size_t SpiUartDevice::write(byte value) {
    /*
     * Write byte to UART.
     */

    while (readRegister(TXLVL) == 0) {
        // Wait for space in TX buffer
    };
    writeRegister(THR, value);
}


size_t SpiUartDevice::write(const char *str, size_t size) {
    /*
     * Write string to UART.
     */

    while (size--)
        write(*str++);

    while (readRegister(TXLVL) < 64) {
        // Wait for empty TX buffer (slow).
        // (But apparently still not slow enough to ensure delivery.)
    };
}

void SpiUartDevice::flush() {
    /*
     * Flush characters from SC16IS750 receive buffer.
     */

    // Note: This may not be the most appropriate flush approach.
    //       It might be better to just flush the UART's buffer
    //       rather than the buffer of the connected device
    //       which is essentially what this does.
    while(available() > 0) {
        read();
    }
}


void SpiUartDevice::ioSetDirection(unsigned char bits) {
    writeRegister(IODIR, bits);
}


void SpiUartDevice::ioSetState(unsigned char bits) {
    writeRegister(IOSTATE, bits);
}

我试图像这样使用它:

SpiSerial.deselect(); //Deselect Wi-Fi
delay(100);           //Wait, just for the heck of it.
currentTemp = thermocouple.readFarenheit(); //Read from max31855... readFarenheit selects and unselects its own SS pin.
SpiSerial.select();   //Reselect Wi-Fi

但它仍然无法运作。我还应该尝试哪些方法才能使其正常运作?

1 个答案:

答案 0 :(得分:6)

两个问题:

  • 您没有提及有关MAX31855库或其使用方法的任何信息。看起来您正在使用Adafruit_MAX31855。您是否将构造函数实例的第二个参数设置为“SS”或者将芯片选择引脚的值设置为MAX31855?他们各自的芯片选择不能共享相同的引脚。

  • Adafruit_MAX31855 bit bangs通过GPIO模拟SPI。这与Wi-Fi真正的硬SPI不同。从spi.begin(); SpiUartDevice::begin()后,与硬SPI共享的GPIO引脚不再可用作GPIO。结果,Adafruit_MAX31855位刘海什么也没做。后一个问题有几种选择。

    • 使用不同的MAX31855磁带库。但我不会很快看到一个。
    • 将Adafruit_MAX31855修复为硬SPI。
    • 除了硬SPI引脚外,MAX31855使用不同的引脚。
    • 使用SPI.end()功能关闭SPI并将GPIO恢复为正常IO使用,然后在敲击Adafruit_MAX31855函数调用后重新启动SPI.begin()

如下:

SpiSerial.deselect(); //Deselect Wi-Fi
SPI.end();            //Restore GPIO mode of pins
delay(100);           //Wait, just for the heck of it
currentTemp = thermocouple.readFarenheit();
SPI.begin();          //Restore SPI mode of pins
SpiSerial.select();   //Reselect Wi-Fi