Gizmo Control Programming Techniques

Gizmo Device Driver and Test Program

The gizmo device driver and test program are available as a single tar-file, gizmo_code.tar.gz.

Device Driver

• A parallel port device driver module is provided for the gizmo, in file daq.c
• Do not compile the Linux kernel with the standard parallel port driver.
• Do remember to load the kernel module daq.ko
• The effects of the read/write operations with this driver are not at all standard.
• write with count=1
  • sends one byte of digital output to the digital port
  • controls the LEDs on the top of the hacksaw blade
  • each bit corresponds to the control of one of the LEDs
  • code example to activate all the LEDs:

           data = 0xff;
           write (gfd, &data, 1);

• write with count=2
  • sends one byte of output to the analog port
  • only the first first byte in data will be used
  • will apply the corresponding number of volts
  • output of 5 will activate the solenoid, pulling the hacksaw blade
  • output of 0 will deactivate the solenoid, releasing the hacksaw blade
  • do not output a value higher than 5; it may harm the circuit
  • code example to activate the solenoid:

          data = 5;
          write (gfd, &data, 2);

  • code example to deactivate the solenoid:

          data = 0;
          write (gfd, &data, 2);

• do not use any other value of count
• read
  • only works for count=2
  • of the 2 bytes read only the first two bits will be needed
  • provides the access to the the two sensors on the sides of the hacksaw blade
  • as the hacksaw blade makes and breaks contact with springs the values will change
  • code example to read the the sensor values:

          read (gfd, &data, 2);

Test Program

• source code is in daq_test.c
• has three modes, controlled by command-line options
• no options tests the LEDs
  • enter CR to step to the next LED
• -i tests the input sensors
  • enter CR to read the values
  • enter control-C to terminate
• -5 tests the solenoid
  • enter CR to shut it back off again

Coding a Periodic Task

• main.c illustrates system calls needed to build a periodic task
• does not use threads, other than the thread of the main program
• use sched_setscheduler() to set priority to system maximum real-time priority
• build a loop around call to clock_nanosleep() with absolute time to schedule periodic delays

A more complete periodic task program is given in periodic.c.

pthreads

rel_jitter_test.c

utils.c

Some common functions:

• int pthread_create(pthread_t * thread, pthread_attr_t * attr, void * (*start_routine)(void *), void * arg);
• int pthread_join(pthread_t th, void **thread_return);
• int pthread_attr_init(pthread_attr_t *attr);
• int pthread_attr_setscope(pthread_attr_t *attr, int scope);
• int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);
• int pthread_attr_setschedparam(pthread_attr_t *attr, const struct sched_param *param);
• int pthread_attr_setinheritsched(pthread_attr_t *attr, int inherit);
• int sched_get_priority_max(int policy);
• int mlockall(int flags);

Libraries needed when linking

• rt
• pthread

Graphs showing effect of real-time priority on release-time jitter

• task not set at high enough priority
• task set at highest real-time priority