Overcomment bitwise operations

Overcomment bitwise operations to provide detailed explanations to each operation and how they work.

main.c

@@ -2,8 +2,8 @@
 #include "common.h"
 
 // PB3 - ADF4350 LE
-// PB2 - SCK to ADF4350 CLK
+// PB2 - USCK to ADF4350 CLK
-// PB1 - DO (MOSI) to ADF4350 DATA
+// PB1 - DO to ADF4350 DATA
 // PB0 - ADF4350 LD
 // PB4 - Lock Status LED
 
@@ -13,7 +13,7 @@ void SendSPIDataADF4350 (uint32_t);
 
 int main()
 {
-  // set instructions to configure the ADF4350 for a 1 GHz +5dBm output
+  // Set instructions to configure the ADF4350 for a 1 GHz +5dBm output.
   uint32_t ar0=0x500000;
   uint32_t ar1=0x8008011;
   uint32_t ar2=0x4e42;
@@ -21,7 +21,7 @@ int main()
   uint32_t ar4=0xac803c;
   uint32_t ar5=0x580005;
 
-  // alternative instructions for a 1001.25 MHz +5dBm output
+  // Alternative instructions for a 1001.25 MHz +5dBm output.
   //uint32_t ar0=0x500008;
   //uint32_t ar1=0x8008029;
   //uint32_t ar2=0x4e42;
@@ -29,41 +29,58 @@ int main()
   //uint32_t ar4=0xac803c;
   //uint32_t ar5=0x580005;
 
-  // set direction of PB1 (DO) and PB2 (USCK) as output
+  // Set direction of PB1 (DO) and PB2 (USCK) as output.
-  DDRB=(1<<PB1)|(1<<PB2);
+  // This is done by using left shift operations.
+  // Binary 1 is shifted by the number of bits specified by PB1 and PB2.
+  // The OR operator is used to "combine" them into one byte,
+  // for example 0b00000010 + 0b00000100 = 0b00000110.
+  // We use DDBx because we are modifying the DDRx register.
+  DDRB = (1 << DDB1) | (1 << DDB2);
 
-  // set to three wire mode (SPI)
+  // Set the USI to three wire SPI mode.
-  USICR=(1<<USIWM0);          
+  // This is done by setting the USI Control Register to a value where only
-  ///USICR=(0<<USIWM1); not needed, already 0
+  // bit position USIWM0 is set to binary one.
+  USICR = (1 << USIWM0);          
 
-  // set direction of PB4 (status LED) as output
+  // Set direction of PB4 (Status LED) as output.
-  DDRB |= (1 << PB4);
+  // Done by shifting 1 into bit position PB4.
+  DDRB |= (1 << DDB4);
 
-  // set direction of PB3 (LE) as open-drain output
+  // Set direction of PB3 (LE) as output.
-  DDRB |= (1 << PB3);
+  // The exact same thing as above but PB3.
+  DDRB |= (1 << DDB3);
 
-  // set PB3 (LE) low
+  // Clear PB3 (LE) state by setting its bit to 0.
-  PORTB &= ~(1 << PORTB3);
+  // First shift 1 into bit position PB3.
+  // ~ is bitwise NOT, and flips all bits.
+  // Finally &= clears PB3 by setting it low, while leaving other bits unchanged.
+  // Unlike the previous lines we use PBx instead of DDBx for bit position,
+  // this is because we are modifying the PORTx register.
+  // So at this point PB3 is configured as an output and is low.
+  PORTB &= ~(1 << PB3);
 
-  // set direction of PB0 (LD Input) as input
+  // Set direction of PB0 (LD Input) as input.
+  // This is done by setting it low using the same method as above.
   DDRB &= ~(1 << DDB0);
 
-  // enable pull-up resistor on PB0
+  // Enable pull-up resistor on PB0
-  PORTB |= (1 << PORTB0);
+  // This is done by setting the state to high,
+  // after configuring as input (above). 
+  PORTB |= (1 << PB0);
 
-  // flash the Status LED (PB4) to show that everything works
+  // Flash the Status LED (PB4) to show that everything works
-  PORTB |= (1 << PORTB4);
+  PORTB |= (1 << PB4);
   Delay(500000);
-  PORTB &= ~(1 << PORTB4);
+  PORTB &= ~(1 << PB4);
   Delay(100000);
 
-  // enter loop waiting for frequency lock to be achieved
+  // Enter loop waiting for frequency lock to be achieved
   while (1)
   {
-      // read the state of LD (PB0)
+      // Read the state of LD (PB0)
       uint8_t ldState = PINB & (1 << PINB0);
 
-      // if LD (PB0) is low, turn on the LED (PB4)
+      // If LD (PB0) is low, turn on the LED (PB4)
       if (ldState == 0)
           PORTB |= (1 << PORTB4); // Turn on the LED
       else
@@ -71,32 +88,33 @@ int main()
   }
 }
 
-// general purpose delay
+// General purpose delay.
 void Delay(uint32_t tmax)
 {
   uint32_t i;
   for (i=0;i < tmax ; i++) 
     {
-    asm("nop");
+      // nop = "no operation", does nothing for 1 cycle.
+      asm("nop");
     }
 }
 
-// send an 8 bit word via SPI1 and receive an 8 bit word at the same time
+// Send an 8 bit word via SPI1 and receive an 8 bit word at the same time
 uint8_t SendReceiveSPIData(uint8_t value)
 {
   uint8_t lout = 0;
   short int i=0;
   
-  // prob change the 8 below to len of value?
+  // Prob change the 8 below to len of value?
   for(i=0;i<8;i++)
   {
-		///USIDR = value[i];		// wrong way to do it apparently, still saving for future reference
+		///USIDR = value[i];		// Wrong way to do it apparently, still saving for future reference
-    USIDR = (value >> i) & 0x01;         // write data bytes in Data register, will cause them to get sent on clock
+    USIDR = (value >> i) & 0x01;         // Write data bytes in Data register, will cause them to get sent on clock
-    while(USIOIF==0)        // check USI data counter overflow flag to detect the end of transmission every byte
+    while(USIOIF==0)        // heck USI data counter overflow flag to detect the end of transmission every byte
     {
-      USICR|=(1<<USICLK)|(1<<USITC);  // enable clock for transmission and generate clock for slave deivce
+      USICR|=(1<<USICLK)|(1<<USITC);  // Enable clock for transmission and generate clock for slave deivce
     }
-    USISR|=(1<<USIOIF);      // clear USI data counter overflow flag
+    USISR|=(1<<USIOIF);      // Clear USI data counter overflow flag
   }
 
   // Read in a 16 bit frame 
@@ -104,22 +122,23 @@ uint8_t SendReceiveSPIData(uint8_t value)
   //return inbyte;
 }
 
-// send a 32 bit register value to the ADF4350
+// Send a 32 bit register value to the ADF4350
 void SendSPIDataADF4350 (uint32_t outval)
 {
-  // split into 4 x 8-bit words
+  // Split into 4 x 8-bit words.
+  // This is done since each "packet" can only be 8-bit.
   uint8_t byte1 = (outval & 0xFF000000) >> 24;
   uint8_t byte2 = (outval & 0x00FF0000) >> 16;
   uint8_t byte3 = (outval & 0x0000FF00) >> 8;
   uint8_t byte4 = outval & 0x000000FF;
 
-  // send these to the ADF4350 via SPI
+  // Send these to the ADF4350 via SPI
   SendReceiveSPIData (byte1);
   SendReceiveSPIData (byte2);
   SendReceiveSPIData (byte3);
   SendReceiveSPIData (byte4);
 
-  // 2 x 16 version:
+  // 2 x 16 version (for reference):
   // split into 2 x 16 bit words
   ///uint16_t highWord = (outval & 0xffff0000) >> 16;
   ///uint16_t lowWord = outval & 0x0000ffff;
@@ -127,12 +146,16 @@ void SendSPIDataADF4350 (uint32_t outval)
   ///SendReceiveSPIData (highWord);
   ///SendReceiveSPIData (lowWord);
 
-  // delay so the clock has gone low before LE is taken high
+  // Delay to make sure the clock has gone low before LE is taken high.
   Delay(10);
-  // pull LE high to load the data into the ADF4350 register
+
-  PORTB |= (1 << PORTB3);
+  // Pull LE high to load the data into the ADF4350 register.
-  // short delay while LE is high (minimum of 20ns)
+  PORTB |= (1 << PB3);
-  Delay(30);
+
-  // pull LE low again
+  // Short delay while LE is high (minimum of 20ns).
-  PORTB &= ~(1 << PORTB3);
+  // This is to make sure the ADF4350 has time to register bits.
+  Delay(100);
+
+  // Pull LE low again.
+  PORTB &= ~(1 << PB3);
 }