I must create a java videogame that runs on a Raspberry Pi 3b and controls external devices. The game is ready. It communicates successfully with a joystick, coin acceptor and 7-segments LED-display. But I can not control a LED-strip. It is the last problem. It uses ws2811 chips that needs the input signal frequency 800 kH. The shortest single signal duration time on my Raspberry Pi 4B, that I can got from Java using functions like:
digitalWrite(pinNumber, HIGH);
is 6500 nanoseconds. But for the LED strip control I need 250 nanoseconds. I have tried the example from Pi4J library. It uses SPI but it doesn't work properly with my LED strip : it switched on random LEDs and doesn't switch off all the LEDs every time I run the allOff() function. I call the allOff() function twice to switch off all the flashing LEDs.
I have only one idea: I know that the same function called from a C program hat the duration time 100 nanoseconds. I want to write a simple program on C and either compile it and call the compiled code from my java code using for example JNI or run this program parallel direct from my Java game. I don't know C, I only know Java but have no experience with JNI. I have wrote the code that I would like to port in C. The program must be pretty simple: I have 10 LEDs in the strip. I need to switch on the LEDs with numbers 1-2, 3-5, 6-10 and have an ability to switch off all the LEDs. The color is only white. My dream abstract code:
public class AbstractLedStripController { //super abstract LED strip controller. I want port this code on C and launch from java
private final static long BIT_0_SIGNAL_START_DURATION = 250; // every bit starts with high level. A single bit transfer durations is 1250 nanoseconds
private final static long BIT_0_SIGNAL_END_DURATION = 1000; // every bit ends with low level. A single bit transfer durations is 1250 nanoseconds
private final static long BIT_1_SIGNAL_START_DURATION = 600; // every bit starts with high level. A single bit transfer durations is 1250 nanoseconds
private final static long BIT_1_SIGNAL_END_DURATION = 650; // every bit ends with low level. A single bit transfer durations is 1250 nanoseconds
private final int LEDs = 10; //Chain contains 10 LEDs. I think it is important that pin supports
private final int signalPin = 10; // Pin number for control the LED. GPIO10 - MOSI pin for SPI. I think it is faster as the anothers
private static long start, end; // Variables for saving time
public void flash1_2(){ //Switch on LEDs from 1 to 2;
changeStatement(0,1);
}
public void flash3_5(){ //Switch on LEDs from 3 to 5;
changeStatement(2,4);
}
public void flash6_10(){ //Switch on LEDs from 6 to 10;
changeStatement(5,9);
}
public void allOff(){ // Color for a single LED is encrypted in 24 bits. To switch off the LED I send 24 logical false
for (int i = 0; i < LEDs; i++){
for (int j = 0; j < 24; j++){
write0();
}
}
}
private void changeStatement(int startPin, int lastPin){
for (int i = 0; i < LEDs; i++){
if (i>= startPin && i <= lastPin){
for (int j = 0; j < 24; j++){ // Color for a single LED is encrypted in 24 bits. For white color I send 24 logical TRUE
write1();
}
}
else {
for (int j = 0; j < 24; j++){ // Color for a single LED is encrypted in 24 bits. To switch off the LED I send 24 logical FALSE
write0();
}
}
}
}
private void write0(){
start = System.nanoTime();
end = start+BIT_0_SIGNAL_START_DURATION;
digitalWrite(true);
while(System.nanoTime()<end){
//wait
}
start = System.nanoTime();
end = start+BIT_0_SIGNAL_END_DURATION;
digitalWrite(false);
while(System.nanoTime()<end){
//wait
}
}
private void write1(){
start = System.nanoTime();
end = start+BIT_1_SIGNAL_START_DURATION;
digitalWrite(true);
while(System.nanoTime()<end){
//wait
}
start = System.nanoTime();
end = start+BIT_1_SIGNAL_END_DURATION;
digitalWrite(false);
while(System.nanoTime()<end){
//wait
}
}
private void digitalWrite(boolean level){
//Something that changes the pin statement very fast
}
}
Give me please an idea what I need to do port this code in C and make it launchable from Java.
