UART write example (#53)

* Rename test functions

* rewrite furi API, segfault

* make fixes in FURI, log through FURI

* add uart write example blank

* implement fuprintf instead of fopencookie

* add gif, blank page

* UART write example description

Co-authored-by: Vadim Kaushan <admin@disasm.info>

wiki/examples/UART-write.md

@@ -0,0 +1,71 @@
+In this example we try to use FURI for interacting between user application and core subsystem.
+
+First of all, we open FURI record by name "tty". This record is used for send some debug/logging info and interact with user by kind-of-TTY (like UART or USB CDC). By default on Flipper target all writes to tty record handled by debug UART (configured by `DEBUG_UART` define). On local target all writes simply prints to stdout.
+
+Open record:
+
+```C
+FuriRecordSubscriber* log = get_default_log();
+```
+
+This is just wrapper on common FURI method:
+
+```C
+furi_open("tty", false, false, NULL, NULL);
+```
+
+"tty" is FURI pipe record. It means that there is no "data" hold in record, it only manage callbacks: when you call `furi_write`, all subscriber's callback is called. You can find default implementation in `core/tty_uart.c`.
+
+Let's get a look at full example code:
+
+```C
+#include "flipper.h"
+#include <string.h>
+#include "log.h"
+
+void application_uart_write(void* p) {
+    // Red led for showing progress
+    GpioPin led = {.pin = GPIO_PIN_8, .port = GPIOA};
+    pinMode(led, GpioModeOpenDrain);
+
+    // get_default_log open "tty" record
+    FuriRecordSubscriber* log = get_default_log();
+
+    // create buffer
+    const char test_string[] = "test\n";
+    furi_write(log, test_string, strlen(test_string));
+
+    // for example, create counter and show its value
+    uint8_t counter = 0;
+
+    while(1) {
+        // continously write it to UART
+        fuprintf(log, "counter: %d\n", counter);
+        counter++;
+
+        // flash at every send
+        digitalWrite(led, LOW);
+        delay(50);
+        digitalWrite(led, HIGH);
+
+        // delay with overall perion of 1s
+        delay(950);
+    }
+}
+```
+
+This code demonstrates two way to work with record:
+
+1. Directly writes some data by `furi_write`
+2. Uses `fuprintf` wrapper on `printf`.
+
+For creating application and set it to autorun, read [Blink example](Blink-app).
+
+_You can also find source of this example in `applications/examples/uart_write.c` and run it by `docker-compose exec dev make -C target_lo example_uart_write`_
+
+![](https://github.com/Flipper-Zero/flipperzero-firmware-community/raw/master/wiki_static/application_examples/example_uart_write.gif)
+
+_Code for target F1 can be compiled by `docker-compose exec dev make -C target_f1 example_uart_write`_
+
+![](https://github.com/Flipper-Zero/flipperzero-firmware-community/raw/master/wiki_static/application_examples/example_uart_write_hw.gif)
+