gpio.c

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <wiringPi.h>
#include <wiringPiSPI.h>

#define GREEN_BUTTON 7
#define RED_BUTTON   3

#define MCP_CHANNEL   0
#define MCP_FREQUENCY 100000

#define DELAY    0
#define DOT_WAVE 30

void error(char *msg) {
  fprintf(stderr, "gpio: %s\n", msg);
  exit(1);
}

void setup_buttons() {
  pinMode(GREEN_BUTTON, INPUT);
  pinMode(RED_BUTTON,   INPUT);
}

void read_buttons() {
  printf("g:%d r:%d ", digitalRead(GREEN_BUTTON), digitalRead(RED_BUTTON));
}

void setup_mcp() {
  if (wiringPiSPISetup(MCP_CHANNEL, MCP_FREQUENCY) == -1) {
    error("could not set up wiringPi SPI");
  }
}

int min = 0;
int max = 0;
char block[] = { 0xe2, 0x96, 0x88, 0x0 };

void read_mcp() {
  uint8_t buffer[] = { 0x01, 0b10100000, 0x00 };
  int result, delta, dots, i;

  wiringPiSPIDataRW(MCP_CHANNEL, buffer, 3);
  result = ((buffer[1] & 3) << 8) + buffer[2];

  delta = (512 - result);

  if (delta > max) max = delta;
  if (delta < min) min = delta;

  printf("d:%-4d mx:%-4d mn:%-4d", delta, max, min);

  dots = delta / DOT_WAVE;

  for (i = -DOT_WAVE; i < 0; i++)
    (dots < i) ? printf("%s", block) : printf(" ");

  for (i = 1; i <= DOT_WAVE; i++)
    (dots > i) ? printf("%s", block) : printf(" ");

  printf("\n");
}

void setup (void) {
  if (geteuid() != 0) {
    error("need to be root");
  }

  if (wiringPiSetup() == -1) {
    error("could not set up wiringPi");
  }

  printf("setup... ");
  fflush(stdout);
  setup_buttons();
  setup_mcp();
  printf("ok\n");
}

int main (void) {
  setup();

  for (;;) {
    read_buttons();
    read_mcp();
    delay(DELAY);
  }
}