Implemented signal a, wrote Makefile and some gdb config

7_segment_display/.gdbinit

@@ -0,0 +1,11 @@
+# Connect to simavr server
+target remote :1234
+
+# Print the registers and code at each step
+def hook-stop
+i r
+disass
+end
+
+# Here you can put a breakpoint to skip some code
+b ENCODE

7_segment_display/Makefile

@@ -3,14 +3,17 @@ BINARY=segment
 AS=avr-as
 LD=avr-ld
 OBJCOPY=avr-objcopy
-AVRDUDE=avrdude
+GDB=avr-gdb
 
+AVRDUDE=avrdude
 AVRDUDE_CONFIG=/etc/avrdude.conf
 
 TTY=/dev/ttyACM0
 
 ARCH=atmega328p
 
+SIMAVR=simavr
+
 build:
 	$(AS) -g -mmcu=$(ARCH) -o $(BINARY).o $(BINARY).s
 	$(LD) -o $(BINARY).elf $(BINARY).o
@@ -19,6 +22,13 @@ build:
 upload:
 	$(AVRDUDE) -C $(AVRDUDE_CONFIG) -p $(ARCH) -c arduino -P $(TTY) -b 115200 -D -U flash:w:$(BINARY).hex:i
 
+sim:
+	$(SIMAVR) -m $(ARCH) $(BINARY).elf -g 
+
+debug:
+	$(GDB) $(BINARY).elf
+
+
 run: build upload
 	
 clean:

7_segment_display/segment.s

@@ -13,6 +13,23 @@
 .equ PORTD, 0x0B
 .equ DDRD,  0x0A
 
+; Aliases for registers. It is easier to develop the logic this way.
+
+.equiv ABIT, 17
+.equiv BBIT, 18
+.equiv CBIT, 19
+.equiv DBIT, 20
+.equiv RESULT, 21
+.equiv TEMP1, 22
+.equiv TEMP2, 23
+
+; Aliases for PINs connected to the 7 segment display. These are the
+; values written in PORTD. DIGITAL PINs 0-6 are connected to PINs a-g
+; of the 7 segment display.
+
+; TO BE IMPLEMENTED
+
+
 .org 0x0000
 
     rjmp INIT
@@ -65,6 +82,68 @@ COUNTER:
 
 ENCODE:
 
+    ; Description:
+    ; -----------
+    ;
+    ;  To represent a digit we will use a 4 bit number looking like this DCBA
+    ;  (A is the LSB and D is the MSB). The equations for the 7 segment display
+    ;  PINs are the following, they can be easily computed using Karnaugh 
+    ;  Diagrams:
+    ;  
+    ;  a = A + C + BD + !B!D
+    ;  b = !B + !C!D + CD
+    ;  c = B + !C + D
+    ;  d = !B!D + C!D + B!CD + !BC + A
+    ;  e = !b!d + C!D
+    ;  f = A + !C!D + B!C + B!D
+    ;  g = A + B!C + !BC + C!D
+    ;
+    ;  Each PIN equation will be computed in r21 and sent to its corresponding 
+    ;  PIN. Other registers will be used to extract the bits from the binary
+    ;  number and to perform logic operations.
+
+    mov ABIT, r24
+    andi ABIT, 0x01
+
+    mov BBIT, r24
+    asr BBIT
+    andi BBIT, 0x01
+
+    mov CBIT, r24
+    asr CBIT
+    asr CBIT
+    andi CBIT, 0x01
+
+    mov DBIT, r24
+    asr DBIT
+    asr DBIT
+    asr DBIT
+
+    ; Compute a. Steps:
+    ;
+    ; 1. Move A in RESULT and perform OR with C
+    ; 2. Move B in TEMP1 and perform AND with B
+    ; 3. Perform OR between (A + C) and BD
+    ; 4. Move B in TEMP1, perform or with D and negate the result (!B!D = !(B + D))
+    ;    (to negate all the bits we will use exclusive or between the register
+    ;     and the value 0xFF)
+    ; 5. Perform OR between (A + C + BD) and !B!D
+
+    mov RESULT, ABIT
+
+    or RESULT, CBIT
+
+    mov TEMP1, BBIT 
+    and TEMP1, DBIT
+    or RESULT, TEMP1
+
+    mov TEMP1, BBIT
+    or TEMP1, DBIT
+    ldi TEMP2, 0xFF
+    eor TEMP1, TEMP2
+    andi TEMP1, 0x01
+    and RESULT, TEMP1
+
     ret
 
 WAIT: