Add license GPLv3

Make project truly open-source by adding GPLv3 license.

LICENSE

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+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
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+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.

README.md

@@ -1,8 +1,18 @@
 # Attiny85 adaptation of Ian Wraith's 2.4GHz Downconverter
 
-STM32 | ATTINY85 | ADF4350
------ | -------- | -------
-PA02  |          | LE
-PA05 (SPI SCK)| PB2 | CLK
-PA07 (SPI MOSI)| PB1 | DATA
-PA11  |          | LD
+An adaption of [this](https://github.com/IanWraith/24DownConvert/tree/master) project for the Attiny85 microcontroller.
+
+Other than the major differences in programming from the original STM32 MCU, this adaptation is functionally the same.
+
+| ATTINY85 | ADF4350  | Purpose
+| -------- | ---------|---------
+| PB3      | LE       | z
+| PB2      | CLK      | SPI Clock
+| PB1      | DATA     | SPI Data line
+| PB5      | LD       | Lock Detection
+| PB4      |          | Status LED+ (anode)
+
+
+Here is a schematic to visualize the connection between the ATTiny85 and the ADF4350:
+
+![Schematic](./screenshots/schematic.png)

main.c

@@ -2,10 +2,10 @@
 #include "common.h"
 
 // PB3 - ADF4350 LE
-// PB2 - SCK to ADF4350 CLK
-// PB1 - DO (MOSI) to ADF4350 DATA
-// PB5 - ADF4350 LD
-// PB4 - Status LED
+// PB2 - USCK to ADF4350 CLK
+// PB1 - DO to ADF4350 DATA
+// PB0 - ADF4350 LD
+// PB4 - Lock Status LED
 
 void Delay(uint32_t);
 uint8_t SendReceiveSPIData(uint8_t);
@@ -13,125 +13,149 @@ void SendSPIDataADF4350 (uint32_t);
 
 int main()
 {
-  // set instructions to configure the ADF4350 for a 1 GHz +5dBm output
-	uint32_t ar0=0x500000;
-	uint32_t ar1=0x8008011;
-	uint32_t ar2=0x4e42;
-	uint32_t ar3=0x4b3;
-	uint32_t ar4=0xac803c;
-	uint32_t ar5=0x580005;
+  // Set instructions to configure the ADF4350 for a 1 GHz +5dBm output.
+  uint32_t ar0=0x500000;
+  uint32_t ar1=0x8008011;
+  uint32_t ar2=0x4e42;
+  uint32_t ar3=0x4b3;
+  uint32_t ar4=0xac803c;
+  uint32_t ar5=0x580005;
 
-  // alternative instructions for a 1001.25 MHz +5dBm output
-	//uint32_t ar0=0x500008;
-	//uint32_t ar1=0x8008029;
-	//uint32_t ar2=0x4e42;
-	//uint32_t ar3=0x4b3;
-	//uint32_t ar4=0xac803c;
-	//uint32_t ar5=0x580005;
+  // Alternative instructions for a 1001.25 MHz +5dBm output.
+  //uint32_t ar0=0x500008;
+  //uint32_t ar1=0x8008029;
+  //uint32_t ar2=0x4e42;
+  //uint32_t ar3=0x4b3;
+  //uint32_t ar4=0xac803c;
+  //uint32_t ar5=0x580005;
 
-  // set direction of PB1 (DO) and PB2 (USCK) as output
-  DDRB=(1<<PB1)|(1<<PB2);
+  // Set direction of PB1 (DO) and PB2 (USCK) as output.
+  // 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)
-  USICR=(1<<USIWM0);          
-  ///USICR=(0<<USIWM1); not needed, already 0
+  // Set the USI to three wire SPI mode.
+  // This is done by setting the USI Control Register to a value where only
+  // bit position USIWM0 is set to binary one.
+  USICR = (1 << USIWM0);          
 
-  // set direction of PB4 (status LED) as output
-  DDRB |= (1 << PB4);
+  // Set direction of PB4 (Status LED) as output.
+  // Done by shifting 1 into bit position PB4.
+  DDRB |= (1 << DDB4);
 
-	// set direction of PB3 (LE) as open-drain output
-	DDRB |= (1 << PB3);
+  // Set direction of PB3 (LE) as output.
+  // The exact same thing as above but PB3.
+  DDRB |= (1 << DDB3);
 
-	// set PB3 (LE) low
-	PORTB &= ~(1 << PORTB3);
+  // Clear PB3 (LE) state by setting its bit to 0.
+  // 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 PB5 (LD Input) as input
-  DDRB &= ~(1 << DDB5);
+  // 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 PB5
-  PORTB |= (1 << PORTB5);
+  // Enable pull-up resistor on PB0
+  // 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
-	PORTB |= (1 << PORTB4);
-	Delay(500000);
-	PORTB &= ~(1 << PORTB4);
-	Delay(100000);
+  // Flash the Status LED (PB4) to show that everything works
+  PORTB |= (1 << PB4);
+  Delay(500000);
+  PORTB &= ~(1 << PB4);
+  Delay(100000);
 
-	// go into an endless loop waiting for frequency lock to be achieved
-	while (1)
-	{
-			// read the state of LD (PB5)
-			uint8_t ldState = PINB & (1 << PINB5);
+  // Enter loop waiting for frequency lock to be achieved
+  while (1)
+  {
+      // Read the state of LD (PB0)
+      uint8_t ldState = PINB & (1 << PINB0);
 
-			// if LD is low, turn on the LED (PB4)
-			if (ldState == 0)
-					PORTB |= (1 << PORTB4); // Turn on the LED
-			else
-					PORTB &= ~(1 << PORTB4); // Turn off the LED
-	}
+      // If LD (PB0) is low, turn on the LED (PB4)
+      if (ldState == 0)
+          PORTB |= (1 << PORTB4); // Turn on the LED
+      else
+          PORTB &= ~(1 << PORTB4); // Turn off the LED
+  }
 }
 
-// general purpose delay
+// General purpose delay.
 void Delay(uint32_t tmax)
 {
-	uint32_t i;
-	for (i=0;i < tmax ; i++) 
-		{
-		asm("nop");
-		}
+  uint32_t i;
+  for (i=0;i < tmax ; i++) 
+    {
+      // 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;
+  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];         // 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
+		///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
+    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 
-	///uint16_t inbyte = *(uint32_t *)(SPI1_BASE + 0x0c);
-	//return inbyte;
+  ///uint16_t inbyte = *(uint32_t *)(SPI1_BASE + 0x0c);
+  //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
-	SendReceiveSPIData (byte1);
-	SendReceiveSPIData (byte2);
+  // Send these to the ADF4350 via SPI
+  SendReceiveSPIData (byte1);
+  SendReceiveSPIData (byte2);
   SendReceiveSPIData (byte3);
   SendReceiveSPIData (byte4);
 
-	// 2 x 16 version:
-	// split into 2 x 16 bit words
+  // 2 x 16 version (for reference):
+  // split into 2 x 16 bit words
   ///uint16_t highWord = (outval & 0xffff0000) >> 16;
-	///uint16_t lowWord = outval & 0x0000ffff;
-	// send these to the ADF4350 via SPI
-	///SendReceiveSPIData (highWord);
-	///SendReceiveSPIData (lowWord);
+  ///uint16_t lowWord = outval & 0x0000ffff;
+  // send these to the ADF4350 via SPI
+  ///SendReceiveSPIData (highWord);
+  ///SendReceiveSPIData (lowWord);
 
-	// delay so 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);
-	// short delay while LE is high (minimum of 20ns)
-	Delay(30);
-	// pull LE low again
-	PORTB &= ~(1 << PORTB3);
+  // 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 << PB3);
+
+  // Short delay while LE is high (minimum of 20ns).
+  // This is to make sure the ADF4350 has time to register bits.
+  Delay(100);
+
+  // Pull LE low again.
+  PORTB &= ~(1 << PB3);
 }