typedef enum {
  ADC_CMD_GET_VALUE,
  ADC_CMD_SET_PIN,
  ADC_CMD_SET_CHANNEL,
  ADC_CMD_SET_CHANNEL_PRESCALLER,
  ADC_CMD_SET_CHANNEL_REFERENCE,
  ADC_CMD_SET_CALLBACK,
  ADC_CMD_UPDATE,
  ADC_CMD_HANDLE,
} adc_cmd_t;

err_hw_t adc_cmd( adc_cmd_t cmd, ... );

#define  ADC_CMD_GET_VALUE      0
#define  ADC_CMD_SET_PIN          1
#define  ADC_CMD_SET_CHANNEL       2
#define  ADC_CMD_SET_CHANNEL_PRESCALLER  3
#define  ADC_CMD_SET_CHANNEL_REFERENCE    4
#define  ADC_CMD_SET_CALLBACK     5
#define  ADC_CMD_UPDATE         6
#define  ADC_CMD_HANDLE    7

adc_cmd (ADC_CMD_SET_CHANNEL,0);

err_hw_t adc_cmd( adc_cmd_t cmd, ... )
{
  va_list args;
  err_hw_t retval = HW_SUCCESS;
  if(adc_init_en == 0) return HW_ERROR;
  va_start(args,cmd);
  switch(cmd)
  {
    case ADC_CMD_GET_VALUE:
      {
        retval = HW_ERROR_CMD;
      }
      break;
    case ADC_CMD_SET_CALLBACK:
      {    
        callback = va_arg( args, adc_callback_t );
      }
      break;
    case ADC_CMD_SET_PIN:
      {
        unsigned int pin       = va_arg( args, unsigned int );
        unsigned int en        = va_arg( args, unsigned int );
        if( pin > 31 )
        {
          retval = HW_ERROR_CMD;
        }
...
...
...