BBB code/GetData_real.c

   1 DataPoint * GetData(int sensor_id, DataPoint * d)
   2 {
   3         //TODO: We should ensure the time is *never* allowed to change on the server if we use gettimeofday
   4         //              Another way people might think of getting the time is to count CPU cycles with clock()
   5         //              But this will not work because a) CPU clock speed may change on some devices (RPi?) and b) It counts cycles used by all threads
   6         gettimeofday(&(d->time_stamp), NULL);
   7
   8         switch (sensor_id)
   9         {
  10                 //TODO: test buffer size on actual hardware
  11                 //              maybe map the sensor path to an array/structure that can be looked up via sensor_id?
  12                 //              not sure about the best place to do unit conversions, especially for nonlinear sensors
  13                 case SENSOR_TEST0:
  14                 {
  15                         int sensor = open("/sys/devices/platform/tsc/ain0", O_RDONLY); //need unique path for each sensor ADC, check path in documentation
  16                         char buffer[128];                                                                                       //ADCs on Beaglebone are 12 bits?
  17                         int read = read(sensor, buffer, sizeof(buffer);
  18                         if (read != -1) {
  19                                 buffer[read] = NULL;                                                                            //string returned by read is not null terminated
  20                                 int value = atoi(buffer);
  21                                 double convert = (value/4096) * 1800;                                           //sample conversion from ADC input to 'true value'
  22                 d->value = convert;
  23                                 lseek(sensor, 0, 0);                                                                            //after read string must be rewound to start of file using lseek
  24             }
  25                         else {
  26                                 perror("Failed to get value from sensor");
  27                         }
  28                         close(sensor);
  29                         break;
  30                 }
  31                 case SENSOR_TEST1:
  32                         int sensor = open("/sys/devices/platform/tsc/ain1", O_RDONLY);
  33                         char buffer[128];
  34                         int read = read(sensor, buffer, sizeof(buffer);
  35                         if (read != -1) {
  36                                 buffer[read] = NULL;
  37                                 int value = atoi(buffer);
  38                                 double convert = (value/4096) * 1800;
  39                 d->value = convert;
  40                                 lseek(sensor, 0, 0);
  41             }
  42                         else {
  43                                 perror("Failed to get value from sensor");
  44                         }
  45                         close(sensor);
  46                         break;
  47                         break;
  48                 }
  49                 //TODO: think about a better way to address individual pins
  50                 //              i.e. pass an int to a separate function that builds the correct filename
  51                 //              doesn't really matter if the pins we're using are fixed though
  52                 case DIGITAL_TEST0:
  53                         int fd = open("/sys/class/gpio/gpio17/value", O_RDONLY)         //again need the right addresses for each pin
  54                         char ch;                                                                                                        //just one character for binary info
  55                         lseek(fd, 0, SEEK_SET);
  56                         int read = read(fd, &ch, sizeof(ch);
  57                         if (read != -1) {
  58                                 if (ch != '0') {
  59                                         d->value = 1;
  60                                 }
  61                                 else {
  62                                         d->value = 0;
  63                                 }
  64                         }
  65                         else {
  66                                 perror("Failed to get value from pin");
  67                         }
  68                         break;
  69                 case DIGITAL_TEST1:
  70                         int fd = open("/sys/class/gpio/gpio23/value", O_RDONLY)
  71                         char ch;
  72                         lseek(fd, 0, SEEK_SET);
  73                         int read = read(fd, &ch, sizeof(ch);
  74                         if (read != -1) {
  75                                 if (ch != '0') {
  76                                         d->value = 1;
  77                                 }
  78                                 else {
  79                                         d->value = 0;
  80                                 }
  81                         }
  82                         else {
  83                                 perror("Failed to get value from pin");
  84                         }
  85                         break;
  86                 default:
  87                         Fatal("Unknown sensor id: %d", sensor_id);
  88                         break;
  89         }
  90         usleep(100000); // simulate delay in sensor polling
  91
  92         return d;
  93 }