Demo of GPIO interrupt

gpio/gpio_interrupt_demo/README.md

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+# BASIC DEMO
+## Introduction
+This is a basic demo of using GPIO interrupts.
+
+## Installation Directions
+This project is intended to be overlayed on top of an existing firmware repo.
+- Clone, Build & Deploy an existing flipper zero firmware repo.  See this [tutorial](/firmware/updating/README.md) for updating firmware.
+- Copy the "gpio_interrupt_demo" [folder](..) to the \applications\plugins\gpio_interrupt_demo folder in your firmware.
+- Build & deploy the firmware.  See this [tutorial](/firmware/updating/README.md) for updating firmware.
+- NOTE: You can also extract the gpio_interrupt_demo.FAP from resources.tar file and use qFlipper to copy the file to the SD Card/apps/Misc folder.
+
+
+## Connecting the hardware
+GPIO pin C3 is our interrupt pin (with internal pull-up resistor).  I connect pin 
+to a 220 ohm resistor and then the other side of the resistor to one side of a
+momentary switch.  Other side of the switch connects to our GND pin.
+
+GPIO A7, A6 and A4 connect to 220ohm resistors then the + or - pins of LED... 
+LED1: +A7  -A6
+LED2: +A6  -A7
+LED3: +A7  -A4
+LED4: +A4  -A7
+LED5: +A6  -A4
+LED6: +A4  -A6
+
+## Running the updated firmware
+These directions assume you are starting at the flipper desktop.  If not, please press the back button until you are at the desktop.
+
+- Press the OK button on the flipper to pull up the main menu.
+- Choose "Applications" from the menu.
+- Choose "GPIO" from the sub-menu.
+- Choose "GPIO Interrupt Demo"
+
+- Message "GND pin C3 to stop." should display
+- LEDs should blink in order.
+- press switch (or connect wire/resistor between C3 and GND)
+- LEDs should stop and display should say "Stopped on LED 4." (or whatever LED was lit.)
+- Press DOWN button on Flipper Zero to start over.
+
+- Press the BACK button to exit.
+
+## How it works
+- application.fam
+  - See [basic demo](../../plugins/basic/README.md) for explanation.
+
+- basic_demo.png
+  - See [basic demo](../../plugins/basic/README.md) for explanation.
+
+- basic_demo_app.c
+  - GPIO specific code:
+    - furi_hal_gpio_init(&gpio_ext_pc3, GpioModeInterruptFall, GpioPullUp, GpioSpeedVeryHigh);
+      - gpio_ext_pc3 is the GPIO pin we are using for interrupt input.
+      - GpioModeInterruptFall - means trigger callback on falling edge (VCC->GND)
+      - GpioModeInterruptRise - means trigger callback on rising edge (GND->VCC)
+      - GpioModeInterruptRiseFall - means trigger callback on either edge
+      - GpioPullUp - Means enable internal pull-up resistor between VCC and pin.
+      - GpioPullDown - Means enable internal pull-down resistor between GND and pin.
+      - GpioPullNo - Means do not enable internal pull-up/pull-down resistor.
+      - GpioSpeedVeryHigh - priority of input?
+    - furi_hal_gpio_add_int_callback(&gpio_ext_pc3, demo_gpio_fall_callback, NULL);
+      - gpio_ext_pc3 is the GPIO pin we are using for interrupt input.
+      - second parameter is callback with signature: "void fnName(void* ctx)"
+      - third parameter is object to pass into callback for context (or NULL if no object).
+      - once furi_hal_gpio_add_int_callback is invoked, the callback is enabled.
+    - demo_gpio_fall_callback(void* ctx)
+      - this method gets invoked by our callback (because of previous add_int_callback) wheneven pin C3 gets pulled to GND.
+      - interrupt callbacks should try to do mininal amount of processing.
+    - furi_hal_gpio_remove_int_callback(&gpio_ext_pc3);
+      - removes the callback, so method is no longer invoked on pin transistion.
+