some handling for video output

build.sh

@@ -9,7 +9,7 @@ rm -f $EXEC_NAME
 # build all source code
 for FILE in $SRC_FOLDER/*.c
 do
-    cc -c $FILE
+    cc -g -c $FILE
 done
 
 # move all objects to appropriate folder
@@ -17,4 +17,4 @@ mkdir -p $OBJ_FOLDER
 mv *.o $OBJ_FOLDER
 
 # create executable out of the objects
-cc -o $EXEC_NAME $OBJ_FOLDER/*.o
+cc -g -o $EXEC_NAME $OBJ_FOLDER/*.o

src/6502.c

@@ -9,6 +9,12 @@ void init()
 {
     // pc is set using 0xFFFC
     pc = read_word(0xFFFC);
+    
+    write_mem(0xD010, 'T');
+    write_mem(0xD010, 'E');
+    write_mem(0xD010, 'S');
+    write_mem(0xD010, 'T');
+    write_mem(0xD010, 'S');
 }
 
 void fetch()
@@ -32,12 +38,11 @@ void decode()
     opcode_in_list = ir;
     opcode_in_table = aaacc;
     
-    
     address_mode = bbb;
     
     if (cc == 0b01)
     {
-        // correct the addressing mode for '01' opcodetype
+        // correct the addressing mode for '01' opcode type
         if (bbb == 0b000)
         {
             address_mode = indirect_x;

src/inc/opcodes.h

@@ -9,7 +9,7 @@ db x;  // x register
 db y;  // y register
 db sp; // stack pointer
 db sr; // status register
-db ir; // intruction register
+db ir; // instruction register
 
 enum opcodes_table
 {       ///        aaa00            aaa01            aaa10
@@ -53,7 +53,7 @@ typedef enum address_mode  am;
 
 am address_mode;
 
-void adc(); // add memory to accumalator with carry
+void adc(); // add memory to accumulator with carry
 void and(); // and memory with accumulator
 void asl(); // shift left one bit (memory or accumulator)
 void bcc(); // branch on carry clear
@@ -96,7 +96,7 @@ void plp(); // pull processor status from stack
 void rol(); // rotate on bit left (memory or accumulator)
 void ror(); // rotate on bit right (memory or accumulator)
 void rti(); // return from interrupt
-void rts(); // retrun from subroutine
+void rts(); // return from subroutine
 void sbc(); // subtract memory from accumulator with borrow
 void sec(); // set carry flag
 void sed(); // set decimal flag

src/main.c

@@ -3,6 +3,7 @@
 
 int main(int argc, char **argv)
 {
+    setbuf(stdout, NULL);
     printf("Apple-I Computer\n");
     
     init(); // start the processor

src/memory.c

@@ -1,6 +1,7 @@
 #include "inc/types.h"
 #include "inc/rom.h"
 #include "inc/memory.h"
+#include <stdio.h>
 
 /*
     
@@ -77,6 +78,11 @@ void write_mem(dw address, db data)
         // 4KB memory RAM
         ram_memory[address] = data;
     }
+    else if (address == 0xD010)
+    {
+        // output character to video
+        printf("%c", data);
+    }
     
     // any other addressed memory will be ignored on write
 }

src/opcodes.c

@@ -38,6 +38,7 @@ void fetch_operand()
             address = read_word(pc);
             operand = read_byte(address);
             pc = pc + 2;
+            break;
         case absolute_x:
             address = read_word(pc);
             address = address + x;
@@ -69,7 +70,7 @@ void fetch_operand()
 
 void adc()
 {
-    // add memory to accumalator with carry
+    // add memory to accumulator with carry
     fetch_operand();
     ac = ac + operand + C_IS_SET;
 }