led blink example

* led blink example

* restore tests

* Update FURI_and_examples.md

wiki/devlog/FURI_and_examples.md

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+One of the most important component of Flipper Core is [FURI](FURI) (Flipper Universal Registry Implementation). It helps control the applications flow, make dynamic linking and interaction between applications.
+
+In fact, FURI is just wrapper around RTOS thread management and mutexes, and callback management.
+
+In this article we create few application, interact between apps, use OS functions and interact with HAL.
+
+# Simple Blink app
+
+First, let's create a simple led blinking application.
+
+## General agreements
+
+Flipper application is just a function:
+
+```C
+void application_name(void* p) {
+    // Setup
+
+    while(1) {
+        // Loop
+    }
+}
+```
+
+1. `void* p` is arbitrary pointer that may be used for pass parameters to application at launch (like argc/argv in POSIX).
+2. Application must never attempt to return or exit from their implementing function.
+3. Avoid long cycles without any "waits" or "blocking" like `delay` or `xQueueReceive`, otherwise your app will blocking overall Flipper work.
+4. Do not create static variables inside function or global variables. Use only local variables. We plan to add virual in-RAM filesystem to save any persistent data.  
+
+## Preparing for launch
+
+We will use integrated LED. Look at the schematic:
+
+![](https://github.com/Flipper-Zero/flipperzero-firmware-community/raw/master/wiki_static/application_examples/leds.png)
+![](https://github.com/Flipper-Zero/flipperzero-firmware-community/raw/master/wiki_static/application_examples/gpio_pa8.png)
+
+This led connect between power rail and GPIO PA8 and we should configure this pin as open drain to properly control led behaviour.
+
+You can find GPIO API in `target_*/flipper_hal.h`. Or if you prefer to use Arduino API, you can find bindings in `core/flipper.h`.
+
+For work with pin we should:
+
+1. Create `GpioPin` instance and specify pin and port.
+2. Configure mode of pin by `pinMode` function.
+3. Control state of pin by `digitalWrite` function.
+
+## Creating application
+
+1. Create new file (for example, `blink.c`) in `applications` folder.
+2. Create code like this:
+
+```C
+#include "flipper.h"
+
+void application_blink(void* p) {
+    // create pin
+    GpioPin led = {.pin = GPIO_PIN_8, .port = GPIOA};
+
+    // configure pin
+    pinMode(led, GpioModeOutput);
+
+    while(1) {
+        digitalWrite(led, HIGH);
+        delay(500);
+        digitalWrite(led, LOW);
+        delay(500);
+    }
+}
+```
+3. To start your application on Flipper startup, add it to autorun:
+    * in `applications/startup.h` add prototype of main application function:
+
+    ```C
+    void application_blink(void* p);
+    ```
+
+    * add entry to `FLIPPER_STARTUP` array (pointer to application function and application name):
+
+    ```C
+    const FlipperStartupApp FLIPPER_STARTUP[] = {
+        #ifdef TEST
+        {.app = flipper_test_app, .name = "test app"}
+        #endif
+
+        // user applications:
+
+        , {.app = application_blink, .name = "blink"}  
+    };
+    ```
+
+4. Add your application file to Makefile (for each target, `target_lo/Makefile` and `target_f1/Makefile`, we add one common makefile later):
+
+```
+# User application
+
+C_SOURCES += ../applications/blink.c
+```
+
+Build and run for linux (target_lo):
+
+`docker-compose exec dev make -C target_lo`
+
+Run:
+
+`docker-compose exec dev target_lo/build/target_lo`.
+
+Зырим как светодиод пытается мигать.
+
+![](https://github.com/Flipper-Zero/flipperzero-firmware-community/raw/master/wiki_static/application_examples/example_blink.gif)
+
+_You also run found source of this example in `applications/examples/blink.c` and run by `docker-compose exec dev make -C target_lo example_blink`_