Question

I always seem to encounter this dilemma when writing low level code for MCU’s.
I never know where to declare pin definitions so as to make the code as reusable as possible.

In this case Im writing a driver to interface an 8051 to a MCP4922 12bit serial DAC.
Im unsure how/where I should declare the pin definitions for The CS(chip select) and LDAC(data latch) for the DAC. At the moment there declared in the header file for the driver.

Iv done a lot of research trying to figure out the best approach but havent really found anything.

Im basically want to know what the best practices… if there are some books worth reading or online information, examples etc, any recommendations would be welcome.

Just a snippet of the driver so you get the idea

/**
    @brief  This function is used to write a 16bit data word  to DAC B -12 data bit plus 4 configuration bits
    @param  dac_data A 12bit word 
    @param  ip_buf_unbuf_select Input Buffered/unbuffered  select bit. Buffered = 1; Unbuffered = 0
    @param  gain_select Output Gain Selection bit. 1 = 1x (VOUT = VREF * D/4096).  0 =2x (VOUT = 2 * VREF * D/4096)
*/
void MCP4922_DAC_B_TX_word(unsigned short int dac_data, bit ip_buf_unbuf_select, bit gain_select)
{                                             

    unsigned char low_byte=0, high_byte=0;
    CS = 0;                                               /**Select the chip*/

    high_byte |= ((0x01 << 7) | (0x01 << 4));            /**Set bit to select DAC A and Set SHDN bit high for DAC A active operation*/
    if(ip_buf_unbuf_select) high_byte |= (0x01 << 6);
    if(gain_select)         high_byte |= (0x01 << 5);

    high_byte |= ((dac_data >> 8) & 0x0F);
    low_byte |= dac_data;
    SPI_master_byte(high_byte);
    SPI_master_byte(low_byte);

    CS = 1;                                               
    LDAC = 0;                                             /**Latch the Data*/
    LDAC = 1;                                         
}

Answer 1

This is what I did in a similar case, this example is for writing an I²C driver:

// Structure holding information about an I²C bus
struct IIC_BUS
{
    int pin_index_sclk;
    int pin_index_sdat;
};

// Initialize I²C bus structure with pin indices
void iic_init_bus( struct IIC_BUS* iic, int idx_sclk, int idx_sdat );

// Write data to an I²C bus, toggling the bits
void iic_write( struct IIC_BUS* iic, uint8_t iicAddress, uint8_t* data, uint8_t length );

All pin indices are declared in an application-dependent header file to allow quick overview, e.g.:

// ...
#define MY_IIC_BUS_SCLK_PIN 12
#define MY_IIC_BUS_SCLK_PIN 13
#define OTHER_PIN 14
// ...

In this example, the I²C bus implementation is completely portable. It only depends on an API that can write to the chip’s pins by index.

Edit:

This driver is used like this:

// main.c
#include "iic.h"
#include "pin-declarations.h"

main()
{
    struct IIC_BUS mybus;
    iic_init_bus( &mybus, MY_IIC_BUS_SCLK_PIN, MY_IIC_BUS_SDAT_PIN );

    // ...

    iic_write( &mybus, 0x42, some_data_buffer, buffer_length );
}