Diff: main.cpp

Revision:

0:eb2258e8c4b5

Child:

1:3c21da72660d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Wed Oct 26 02:02:09 2016 +0000
@@ -0,0 +1,159 @@
+#include "mbed.h"
+
+extern "C" void my_wait_us_asm (int n);
+
+DigitalOut myled(LED1);
+Serial pc(USBTX, USBRX); // tx, rx
+DigitalInOut data(PA_8);
+DigitalIn button(PC_13);
+
+// 0 is 3 microseconds low followed by 1 microsecond high
+// 1 is 1 microsecond low followed by 3 microseconds high
+unsigned int GetMiddleOfPulse()
+{
+    // wait for line to go high
+    while(1)
+    {
+        if(data.read() == 1) break;
+    }
+    
+    // wait for line to go low
+    while(1)
+    {
+        if(data.read() == 0) break;
+    }
+    
+    // now we have the falling edge
+    // wait 2 microseconds to be in the middle of the pulse, and read. high --> 1.  low --> 0. 
+    my_wait_us_asm(2);
+    return (unsigned int) data.read();
+}
+
+// continuously read bits until at least 9 are read, confirm valid command, return without stop bit
+unsigned int readCommand()
+{
+    unsigned int command = GetMiddleOfPulse(), bits_read = 1;
+    
+    while(1) // read at least 9 bits (2 bytes + stop bit)
+    {
+        //my_wait_us_asm(4);
+        command = command << 1; // make room for the new bit
+        //command += data.read(); // place the new bit into the command
+        command += GetMiddleOfPulse();
+        command &= 0x1FF; // remove all except the last 9 bits
+        
+        bits_read++;
+        
+        if(bits_read >= 9) // only consider when at least a whole command's length has been read
+        {
+            if(command == 0x3 || command == 0x1 || command == 0x1FF)
+            {
+                // 0x3 = 0x1 + stop bit --> get controller state
+                // 0x1 = 0x0 + stop bit --> who are you?
+                // 0x1FF = 0xFF + stop bit --> reset signal
+                command = command >> 1; // get rid of the stop bit
+                return command;
+            }
+        }
+    }
+}
+
+void write_1()
+{
+    data = 0;
+    my_wait_us_asm(1);
+    data = 1;
+    my_wait_us_asm(3);
+    //data = 0;
+    //pc.printf("1");
+}
+
+void write_0()
+{
+    data = 0;
+    my_wait_us_asm(3);
+    data = 1;
+    my_wait_us_asm(1);
+    //data = 0;
+    //pc.printf("0");
+}
+
+
+void sendStop()
+{
+    data = 0;
+    my_wait_us_asm(1);
+    data = 1;
+}
+
+void sendByte(unsigned char b)
+{
+    //pc.printf("\nTrying to send 0x%x\n",b);
+    for(int i = 0;i < 8;i++) // send all 8 bits, one at a time
+    //for(int i = 7;i >= 0;i--) // send all 8 bits, in reverse order, one at a time
+    {
+        if((b >> i) & 1)
+        {
+            write_1();
+        }
+        else
+        {
+            write_0();
+        }
+    }
+}
+
+int main()
+{
+    __disable_irq();    // Disable Interrupts
+    pc.printf("SystemCoreClock = %d Hz\n", SystemCoreClock);
+    
+    while(1)
+    {
+        // Set pin mode to input
+        data.input();
+        
+        // Read command
+        unsigned int cmd = readCommand();
+        
+        //pc.printf("Read command: %u\n", cmd);
+        
+        my_wait_us_asm(2); // wait a small amount of time before replying
+        
+        // Set pin mode to output
+        data.output();
+        
+        switch(cmd)
+        {
+            case 0x00: // identity
+            case 0xFF: // reset
+                //pc.printf("Received identity ");
+                // reply 0x05, 0x00, 0x02
+                sendByte(0x05);
+                sendByte(0x00);
+                sendByte(0x02);
+                sendStop();
+                break;
+            case 0x01: // poll for state
+                if(!button.read()) // simulate Start pressed
+                {
+                    sendByte(0x08); // I think this is start, 4th bit
+                    sendByte(0x00);
+                    sendByte(0x00);
+                    sendByte(0x00);
+                    sendStop();
+                    break;
+                }
+                else
+                {
+                    // respond with controller state
+                    sendByte(0x00);
+                    sendByte(0x00);
+                    sendByte(0x00);
+                    sendByte(0x00);
+                    sendStop();
+                    break;
+                }
+        }
+    }
+}