Improve flag handling for emulator

utils/emul.c

@@ -10,10 +10,31 @@ union regset {
   uint16_t r16[8]; // AX, CX, DX, BX, SP, BP, SI, DI
 } regset;
 
-int carry, zero;
+typedef struct flagbits {
+  unsigned int c : 1;
+  unsigned int u1 : 1;
+  unsigned int p : 1;
+  unsigned int u3 : 1;
+
+  unsigned int a : 1;
+  unsigned int u5 : 1;
+  unsigned int z : 1;
+  unsigned int s : 1;
+
+  unsigned int t : 1;
+  unsigned int i : 1;
+  unsigned int d : 1;
+  unsigned int o : 1;
+
+  unsigned int u12 : 4;
+} flagbits;
+
+union flags {
+  uint16_t reg;
+  struct flagbits bit;
+} flags;
 
 uint16_t ip = 0x100;
-uint16_t flags = 0;
 uint16_t scratch;
 uint16_t reg;
 int off;
@@ -25,7 +46,19 @@ void* rmptr;
 #define R8(x) regset.r8[fixr8ref(x)]
 #define R16(x) regset.r16[x]
 
+#define FLAGMASK 0xF02A
+#define CF 0
+#define PF 2
+#define AF 4
+#define ZF 6
+#define SF 7
+#define TF 8
+#define IF 9
+#define DF 10
+#define OF 11
+
 #define AL regset.r8[0]
+#define AH regset.r8[1]
 #define CL regset.r8[2]
 #define DL regset.r8[4]
 #define AX regset.r16[0]
@@ -54,6 +87,16 @@ void dump() {
   for (i=0; i<8; i++) {
     printf("%s=%04X ", regnames[i], regset.r16[i]);
   }
+  printf("%c", flags.bit.o ? 'O' : '-');
+  printf("%c", flags.bit.d ? 'D' : '-');
+  printf("%c", flags.bit.i ? 'I' : '-');
+  printf("%c", flags.bit.t ? 'T' : '-');
+  printf("%c", flags.bit.s ? 'S' : '-');
+  printf("%c", flags.bit.z ? 'Z' : '-');
+  printf("%c", flags.bit.a ? 'A' : '-');
+  printf("%c", flags.bit.p ? 'P' : '-');
+  printf("%c", flags.bit.c ? 'C' : '-');
+
   printf("\n");
   printf("IP=%04X : %02X %02X\n", ip, mem[ip], mem[ip+1]);
 }
@@ -65,17 +108,16 @@ void arith8(int op, int8_t* dst, int src) {
   switch (op) {
   case ADD:  t += src; break;
   case OR:   t |= src; break;
-  case ADC:  t += (src + carry); break;
+  case ADC:  t += (src + flags.bit.c); break;
-  case SBB:  t -= (src + carry); break;
+  case SBB:  t -= (src + flags.bit.c); break;
   case AND:  t &= src; break;
   case SUB:  t -= src; break;
   case XOR:  t ^= src; break;
   case CMP:  t -= src; break;
   case TEST: t &= src; break;
   }
-  zero=!t;
+  flags.bit.z = !t;
-  // I dont think the following is correct
+  flags.bit.c = !!((t ^ p) >> 8);
-  carry=((t ^ p) >> 8) & 1;
   if (op==CMP || op==TEST) return;
   *dst = t;
 }
@@ -87,25 +129,20 @@ void arith16(int op, int16_t* dst, int src) {
   switch (op) {
   case ADD:  t += src; break;
   case OR:   t |= src; break;
-  case ADC:  t += (src + carry); break;
+  case ADC:  t += (src + flags.bit.c); break;
-  case SBB:  t -= (src + carry); break;
+  case SBB:  t -= (src + flags.bit.c); break;
   case AND:  t &= src; break;
   case SUB:  t -= src; break;
   case XOR:  t ^= src; break;
   case CMP:  t -= src; break;
   case TEST: t &= src; break;
   }
-  zero=!t;
+  flags.bit.z = !t;
-  // I dont think the following is correct
+  flags.bit.c = !!((t ^ p) >> 8);
-  carry=((t ^ p) >> 16) & 1;
   if (op==CMP || op==TEST) return;
   *dst = t;
 }
 
-uint16_t get_flags() {
-  return (carry & 1) | ((zero & 1)<< 6);
-}
-
 int fixr8ref(int r) {
   return ((r << 1) & 0b110) | ((r >> 2) & 0b1);
 }
@@ -182,7 +219,7 @@ uint16_t pop() {
   return v;
 }
 
-void handle_syscall(int number) {
+void cpm_syscall(int number) {
   switch(number) {
   case 0:
     exit(0);
@@ -191,7 +228,18 @@ void handle_syscall(int number) {
     printf("%c", DL);
     break;
   default:
-    fprintf(stderr, "Fatal: Unhandled syscall CL=%Xh\n", number);
+    fprintf(stderr, "Fatal: Unhandled CP/M syscall %Xh\n", number);
+    exit(1);
+  }
+}
+
+void dos_syscall(int number) {
+  switch(number) {
+  case 0:
+    exit(0);
+    break;
+  default:
+    fprintf(stderr, "Fatal: Unhandled DOS syscall %Xh\n", number);
     exit(1);
   }
 }
@@ -199,10 +247,13 @@ void handle_syscall(int number) {
 void handle_intr(int number) {
   switch(number) {
   case 0x20:
-    handle_syscall(0);
+    dos_syscall(0);
+    break;
+  case 0x21:
+    dos_syscall(AH);
     break;
   case 0xE0:
-    handle_syscall(CL);
+    cpm_syscall(CL);
     break;
   default:
     fprintf(stderr, "Fatal: Unhandled interrupt %Xh\n", number);
@@ -270,7 +321,7 @@ void step() {
     R16(reg) = RM16;
     break;
   case 0x9C: // PUSHF
-    push(get_flags());
+    push(flags.reg | FLAGMASK);
     break;
   case 0xA1: // MOV AX,memoffs16
     AX = *(uint16_t*)&mem[imm16()];
@@ -299,7 +350,7 @@ void step() {
   case 0xE8: // CALL rw
     reg = ip + (int16_t)imm16();
     if (reg == 5) {
-      handle_syscall(CL);
+      cpm_syscall(CL);
     } else {
       push(ip);
       ip = reg;
@@ -338,20 +389,46 @@ void copy_cmdline(char* str) {
 int main(int argc, char** argv) {
   memset(&mem, sizeof(mem), 0);
   memset(&regset, sizeof(regset), 0);
+  // Prepare default exit into int 20h
   mem[0]=0xCD;
   mem[1]=0x20;
   push(0);
 
-  if (argc>2) {
+  argc--;
-    copy_cmdline(argv[2]);
+  argv++;
+
+  while(argc && argv[0][0]=='-') {
+    switch(argv[0][1]) {
+    case 't':
+      flags.bit.t = 1;
+      break;
+    default:
+      fprintf(stderr, "Unknown option %s\n", argv[0]);
+      exit(1);
+      break;
+    }
+    argc--;
+    argv++;
+  }
+
+  if (argc) {
+    FILE* fd = fopen(argv[0], "r");
+    fread(mem + ip, 1, sizeof(mem) - ip, fd);
+    argc--;
+    argv++;
+  } else {
+    fprintf(stderr, "No COM file specified\n");
+    exit(1);
+  }
+
+  if (argc) {
+    copy_cmdline(argv[0]);
   } else {
     copy_cmdline("");
   }
 
-  FILE* fd = fopen(argv[1], "r");
-  fread(mem + ip, 1, sizeof(mem) - ip, fd);
   while(1) {
     step();
-    dump();
+    if (flags.bit.t) dump();
   }
 }