Review

• Breadboard circuits (LED + 2 types of button)
• C programs to control GPIO pins (gpio.h)
  • Setup pin to be output, have LED Blink when set
  • Setup pin to be input, have button change variable

GPIO C Programming

• lets just use gpio.h in C
  • why do it in ARM Assembly?
• we read and write to specific memory addresses to control the Pi's GPIO pin voltages
  • GPFSEL0, GPFSEL1,..., GPSEL5
  • GPSET0, GPSET1
  • GPCLR0, GPSET1
  • GPLEV0, GPLEV1

Today:

• Interrupt-driven programming
  • see what assignment 3 demo should look like
  • 05_GPIO_PushButton_Interrupt as toy example
    • wire breadboard for this program
    • compile and run code
    • review code
    • add switch A, falling edge type, interrupt control to decrement counter
  • extra time? outline steps to do assignment

Breakdown of interrupt code

• includes

  • "sysreg.h" for enableIRQ();

  • "irq.h" for IRQ_ENABLE_IRQS_2

• sharedValue
  • outside of main, in main, and in handlers.c
• while loop
  • main take away: the sharedValue can change at any time, i.e. during the busy loop
• init_GPIO_to_risingEdgeInterrupt()

  • *GPREN0 = (0x1 << 17);

  • *IRQ_ENABLE_IRQS_2 = (0x1 << 20);

• handers.c
  • IRQ_handler() runs for all of our interrupts

  • sharedValue++

Add decrement button interrupt

• places to modify code:
  • main.c
    • define init_GPIO18_to_fallingEdgeInterrupt()
      • copy code from init_GPIO17_to_....
      • GPREN0 should be replaced with GPFED0
      • 17 should be replaced with 18
    • in main()
      • add your new init function
  • handler.c
    • add condition for ( *GPEDS0 == (0x1 << 18) ) to decrement sharedValue

Recommended assignment steps

• start with GPIO_PushButtonInterrupt code
• get single state program running
  • remove printing of program and exception state info
  • add back LED control functions from other toy examples.
    • init_GPIO_to_output(), set_GPIO(), and clear_GPIO()
    • either replicate these LED control functions (and calls in main()) for each LED pin numbers or abstract the functions to take pin number argument.
  • infinite loop in main() just calls light_next(current_LED)

More steps...

• add states
  • sharedValue -> current state
  • modify handler.c

• reparameterize light_next and busy_loop functions to also take state parameters i.e., speed and order
• write helper functions e.g. busy_loop(int time)
• rewrite infinite loop

Final steps...

• fill in all the details I missed
• test and debug from the beginning
• submit on D2L