SPI Example

This page describes the SPI example provided in the code examples and will discuss certain sections of the program. Code examples can be found in the examples folder within the repository.

/********************************************************
 *   File Name: spi_ex.c
 *
 *   Description:
 *              Main file
 *
 *
 *********************************************************/

/*************************************************************************
 System Includes
 ************************************************************************/
#include "sublibinal.h"
#include "sublibinal_config.h"

//forward declarations
void timer_callback(void);

/*************************************************************************
 Main Function
 ************************************************************************/
int main(void) {

    //buffer for uart ISRs
    uint8 spi_tx_buffer[128];

    //structures for configuring peripherals
    SPI_Config spi_config = {0};
    Timer_Config timer_config = {0};

    //setup peripherals
    timer_config.which_timer = Timer_1; //Specify that we will be using timer 1
    timer_config.frequency = 1000; //Specify that the timer operates at 1KHz
    timer_config.pbclk = PB_CLK; //specify the speed of the peripheral bus clock
    timer_config.callback = &timer_callback; //Link a callback function for the ISR
    timer_config.enabled = 1; //Enable the Timer
    initialize_Timer(timer_config); //Initialize the Timer

    spi_config.which_spi = SPI_CH_1; //Specify that we will use SPI Channel 1
    spi_config.pb_clk = PB_CLK; //Tell the module the speed of our clock, 15MHz
    spi_config.speed = 100000; //Tell SPI module the frequency that we are talking at, 100KHz
    spi_config.tx_en = 1; //Enable the SPI module
    spi_config.clk_edge = falling; //Specify that SPI transition from a high to low transition
    spi_config.tx_buffer_ptr = spi_tx_buffer; //Hand a pointer to the data buffer
    spi_config.tx_buffer_size = sizeof(spi_tx_buffer); //tell it the size of the data buffer
    initialize_SPI(spi_config); //Initialize the SPI module
 
    //Global interrupt enable. Do this last!
	enable_Interrupts();

    while (1) {
        //put background tasks here
    }

    return 0;
}

void timer_callback(void)
{
    uint8 data[3];

    data[0] = 'a';
    data[1] = 'b';
    data[2] = 'c';

    //send some SPI data
    send_SPI(SPI_CH_1, data, sizeof(data));
    
    
}

In this program, a timer callback is used to send SPI communications down SPI channel 1 at a rate of 1 KHz. The first section of important code is the SPI configuration.

    SPI_Config spi_config = {0};
    //....
    spi_config.which_spi = SPI_CH_1; //Specify that we will use SPI Channel 1
    spi_config.pb_clk = PB_CLK; //Tell the module the speed of our clock, 15MHz
    spi_config.speed = 100000; //Tell SPI module the frequency that we are talking at, 100KHz
    spi_config.tx_en = 1; //Enable the SPI module
    spi_config.clk_edge = falling; //Specify that SPI transition from a high to low transition
    spi_config.tx_buffer_ptr = spi_tx_buffer; //Hand a pointer to the data buffer
    spi_config.tx_buffer_size = sizeof(spi_tx_buffer); //tell it the size of the data buffer
    initialize_SPI(spi_config); //Initialize the SPI module

In this section of code, we initialize the structure to NULL to avoid issues with residual values in memory. If structures are not nullified, there is no guarentee that callback function members are not null. If they are not null and do not point to functions within the program, the program will malfunction. We configure the SPI module to talk at a speed of 100KHz utilizing SPI channel 1. We also specify that this SPI will be only used for transmission. Finally, we initialize the SPI module.

The next important section is the transmission of data.

void timer_callback(void)
{
    uint8 data[3];
    data[0] = 'a';
    data[1] = 'b';
    data[2] = 'c';

    //send some SPI data
    send_SPI(SPI_CH_1, data, sizeof(data));
}

In the timer callback function, we create an array of three characters and transmit them utilizing SPI channel 1. In this case, we are sending a constant string of characters 'abc'.

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