It's working now.

Fixes include:
* It's working now. ;-)
* Added new commands:
  * ? returns a help via Serial
  * r sets every LED to a random color
  * t sets the whole strip to green
* Afte receiving the first command, the status LED changes for every received command.

.gitignore

@@ -0,0 +1,5 @@
+.pio
+.vscode/.browse.c_cpp.db*
+.vscode/c_cpp_properties.json
+.vscode/launch.json
+.vscode/ipch

include/main.h

@@ -5,8 +5,12 @@ void cmd_output();
 void cmd_clear();
 void cmd_version();
 void cmd_get_max();
+void cmd_random_color();
+void cmd_test();
+void cmd_help();
 void send_nack();
 void send_ack();
+void send(byte data);
 void status_led_on();
 void status_led_off();
 void status_led_toggle();

src/main.cpp

@@ -4,7 +4,7 @@
 #define WS2812B_PIN 14
 #define LED_DATA_PIN  13 // D7 // Hardware-MOSI
 #define LED_CLOCK_PIN 14 // D5 // Hardware-CLK
-#define STATUS_LED_PIN 1
+#define STATUS_LED_PIN 16
 #define FIRMWARE_VERSION_MAJOR 1
 #define FIRMWARE_VERSION_MINOR 3
 #define MAX_LED_COUNT 10000
@@ -17,11 +17,13 @@ unsigned long blink_mode_timeout_timer_ts;
 
 
 void setup() {
-	Serial.begin(115200);
+	Serial.begin(9600);
+	Serial.setTimeout(1);
+	//Serial.println("Online!");
 	led_count = 256;
 	leds = new CRGB[256];
 	//FastLED.addLeds<WS2812B, WS2812B_PIN, GRB>(leds, 256);
-	FastLED.addLeds<APA102, LED_DATA_PIN, LED_CLOCK_PIN>(leds, 256);
+	FastLED.addLeds<APA102, LED_DATA_PIN, LED_CLOCK_PIN, GRB, DATA_RATE_MHZ(1)>(leds, 256);
 	FastLED[0].setLeds(leds, 256);
 	pinMode(STATUS_LED_PIN, OUTPUT);
 	set_blink(0);
@@ -29,9 +31,11 @@ void setup() {
 }
 
 void loop() {
-	if (Serial.available()) {
-		byte recv = Serial.read();
-		switch(recv) {
+	Serial.setTimeout(1);
+	byte buffer=0;
+	size_t received = Serial.readBytes(&buffer, 1);
+	if (received==1) {
+		switch(buffer) {
 			case 'L': cmd_length(); break;
 			case 'F': cmd_fill(); break;
 			case 'R': cmd_receive(); break;
@@ -39,6 +43,9 @@ void loop() {
 			case 'C': cmd_clear(); break;
 			case 'V': cmd_version(); break;
 			case 'M': cmd_get_max(); break;
+			case 'r': cmd_random_color(); break;
+			case 't': cmd_test(); break;
+			case '?': cmd_help(); break;
 			default: send_nack(); break;
 		}
 		set_blink(1);
@@ -68,7 +75,7 @@ void blink() {
 			}
 			break;
 		case 1: // active after receiving a command - ends after 500ms
-			if(blink_timer > 30) {
+			/*if(blink_timer > 30) {
 				blink_timer_ts = now;
 				status_led_toggle();
 			}
@@ -88,7 +95,11 @@ void blink() {
 			} else {
 				blink_timer_ts = now;
 				status_led_off();
-			}
+			}*/
+			status_led_toggle();
+			set_blink(2);
+			break;
+		case 2: // do nothing
 			break;
 		default: // should newer be reached
 			if (blink_timer > 1000) {
@@ -123,7 +134,7 @@ void cmd_fill() {
 void cmd_receive() {
 	uint16_t first_led = receive_word();
 	uint16_t cmd_leds = receive_word();
-	if (first_led <= led_count && cmd_leds>0 && first_led + cmd_leds + 1 <= led_count) {
+	if (first_led <= led_count && cmd_leds>0 && first_led + cmd_leds <= led_count) {
 		uint16_t end_led = first_led + cmd_leds;
 		for(uint16_t i=first_led; i<end_led; i++) {
 			leds[i] = receive_color();
@@ -156,26 +167,67 @@ void cmd_clear() {
 }
 
 void cmd_version() {
-	Serial.write(FIRMWARE_VERSION_MAJOR);
-	Serial.write(FIRMWARE_VERSION_MINOR);
+	send(FIRMWARE_VERSION_MAJOR);
+	send(FIRMWARE_VERSION_MINOR);
 	send_ack();
 }
 
 void cmd_get_max() {
 	Serial.write(MAX_LED_COUNT >> 8);
-	Serial.write(MAX_LED_COUNT & 0xFF);
+	send((byte)(MAX_LED_COUNT & 0xFF));
+	send_ack();
+}
+
+void cmd_random_color() {
+	for (int i=0; i<led_count; i++) {
+		leds[i] = CRGB(random8(), random8(), random8());
+	}
+	FastLED.show();
+	send_ack();
+}
+
+void cmd_test() {
+	for (int i=0; i<led_count; i++) {
+		leds[i] = CRGB::Red;
+	}
+	FastLED.show();
+	send_ack();
+}
+
+void cmd_help() {
+	Serial.println("L <length>                  Set new LED strip length.");
+	Serial.println("F <start> <count> <color>   Fills the given part with color.");
+	Serial.println("R <start> <count> <color>[] Sets colors for the fiven area.");
+	Serial.println("O                           Shows the set colors on the strip.");
+	Serial.println("C                           Sets all LEDs to black.");
+	Serial.println("V                           Returns the firmware version as two bytes.");
+	Serial.println("M                           Returns the maximum number of LEDs.");
+	Serial.println("r                           Sets all LEDs to random colors.");
+	Serial.println("t                           Sets the whole strip to red.");
+	Serial.println("?                           Displays this help.");
 	send_ack();
 }
 
 void send_ack() {
-	Serial.write('A');
+	send('A');
 }
 
 void send_nack() {
-	Serial.write('N');
+	send('N');
+}
+
+void send(byte data) {
+	Serial.write(data);
+	//Serial.write(0x00);
+	Serial.flush();
 }
 
 uint8_t receive_byte() {
+	/*byte buffer;
+	Serial.setTimeout(5);
+	size_t count = Serial.readBytes(&buffer, 1);
+	if (count==1) return buffer;
+	else return 0;*/
 	while (!Serial.available()) {}
 	return Serial.read();
 }