Unable to debug the spi_master example demo code

[rewatee_poonia]

Hi There

I am debugging the example code of lpc17xx SPI master.

Problem: data is not copying in the SPDR data registor.

[Alice_Yang]

Hello rewatee poonia,

In SPI model of LPC17xx, there is no buffer between the data register and the internal shift register. A write to the
data register goes directly into the internal shift register, so we can not read the send data in SPI Data Register (S0SPDR).

The SPI Data Register (S0SPDR) is used to provide the transmit and receive data bytes, Read data is buffered.
When a transfer is complete, the receive data is transferred to a single byte data buffer, where it is later read. A read of the SPI Data Register returns the value of the read data buffer.

About the detail you also can have a look at User manual of your chip , the SPI part:

Have a great day,
TIC

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[rewatee_poonia]

Hello   Alice_Yang

I have tried the SPI example with Open LPC1768(Master) microcontroller and Arduino Mega 2560(Slave).

problem: The data is not getting at the slave arduino.

I have tried the SPI communication between two arduino mega(MASTER & SLAVE). In that case SPDR is updating. Whatever data i am sending from master, it is getting receive at slave device.

** In case of open LPC1768  it is not working. I am receiving 0 at slave. 

SPI master code (Example code from cmsis library)

I did some changes in spi_master.c

1. mode 0->CPHA  & CPOL =0

      SPI_ConfigStruct.CPHA = SPI_CPHA_FIRST;
      SPI_ConfigStruct.CPOL = SPI_CPOL_HI;

2.    #define SPI_DATABIT_SIZE    8

         /** Max buffer length */
      #define BUFFER_SIZE    1

3. 

         void Buffer_Init(void)
               {
                     uint32_t i;
                     for (i = 0; i < BUFFER_SIZE; i++) {
                     Tx_Buf[i] = i+1;
                     Rx_Buf[i] = 0;
                     }
                  }

Arduino slave code

//SPI SLAVE (ARDUINO)
#include<SPI.h>
#define LEDpin 13
volatile boolean received;
volatile byte Slavereceived,Slavesend;
void setup()

{
Serial.begin(115200);
pinMode(LEDpin,OUTPUT); // Setting pin 7 as OUTPUT
pinMode(MISO,OUTPUT); //Sets MISO as OUTPUT (Have to Send data to Master IN
SPI.beginTransaction(SPISettings(2500000, MSBFIRST, SPI_MODE0));
SPCR |= _BV(SPE); //Turn on SPI in Slave Mode
SPCR |= _BV(SPIE);
received = false;

//SPI.attachInterrupt(); //Interuupt ON is set for SPI commnucation

}

ISR (SPI_STC_vect) //Inerrrput routine function
{
Slavereceived = SPDR; // Value received from master if store in variable slavereceived
received = true; //Sets received as True
}

void loop()

{

if(received) //Logic to SET LED ON OR OFF depending upon the value recerived from master
{
if (Slavereceived==1)
{
digitalWrite(LEDpin,HIGH); //Sets pin 7 as HIGH LED ON
Serial.println("Slave LED ON");
Serial.println(Slavereceived);
}else
{
digitalWrite(LEDpin,LOW); //Sets pin 7 as LOW LED OFF
Serial.println("Slave LED OFF");
Serial.println(Slavereceived);
}
Slavesend = 2;
SPDR = Slavesend; //Sends the  value to master via SPDR
delay(1000);
}
}

[Alice_Yang]

Hello rewatee ,

First of all , we should confirm  there is right output signal on MOSI of LPC1768,  Please use logic analyzer check it .

[rewatee_poonia]

HelloAlice_Yang

I have checked. There is no data available on MOSI pin and clock pin.