Application - LPC1768, SPI communication

Hardware

RPi GPIO

NXP LPC1768 pinout

SPI timing

RPi2               NXP LPC1768
MOSI(GPIO10)  --   MOSI(p5)
MISO(GPIO09)  --   MISO(p6)
SCLK(GPIO11)  --   SCLK(p7)
CE0(GPIO08)   --   (p8)

Software

• RPi using libbcm2835
  • gcc -o spi spi.c -lbcm2835
  • unknown why BCM2835_SPI_MODE1 is more stable??

#include <bcm2835.h>
#include <stdio.h>

int main(int argc, char **argv)
{
      if (!bcm2835_init())
        return 1;

    bcm2835_spi_begin();
    bcm2835_spi_setBitOrder(BCM2835_SPI_BIT_ORDER_MSBFIRST);      // The default
    bcm2835_spi_setDataMode(BCM2835_SPI_MODE1);                   // The default
    bcm2835_spi_setClockDivider(BCM2835_SPI_CLOCK_DIVIDER_65536); // The default
    bcm2835_spi_chipSelect(BCM2835_SPI_CS0);                      // The default
    bcm2835_spi_setChipSelectPolarity(BCM2835_SPI_CS0, LOW);      // the default    

    // Send a byte to the slave and simultaneously read a byte back from the slave
    // If you tie MISO to MOSI, you should read back what was sent
    uint8_t data = bcm2835_spi_transfer(0x12);
    printf("Read from SPI: %02X\n", data);

    bcm2835_spi_end();
    bcm2835_close();
    return 0;
}

• NXP LPC1768

#include "mbed.h"

SPISlave device(p5, p6, p7, p8); // mosi, miso, sclk, ssel

Serial pc(USBTX, USBRX); 
int main() {
	device.reply(0x00);              // Prime SPI with first reply
	while(1) {
		if(device.receive()) {
			int v = device.read();   // Read byte from master
			device.reply(v);         // Make this the next reply
			pc.printf("reply: %02x\n", v);
		}
	}
}

Reference

• How to Delay SPI Slave to Master Response?

• Use the Raspberry Pi SPI Interface to Connect to a Device

• wiki, Serial Peripheral Interface Bus

• libbcm2835

• Raspberry Pi SPI