asm_files/list-0051.asm

@@ -1,30 +0,0 @@
-; ========================================================================
-;
-; (C) Copyright 2023 by Molly Rocket, Inc., All Rights Reserved.
-;
-; This software is provided 'as-is', without any express or implied
-; warranty. In no event will the authors be held liable for any damages
-; arising from the use of this software.
-;
-; Please see https://computerenhance.com for further information
-;
-; ========================================================================
-
-; ========================================================================
-; LISTING 51
-; ========================================================================
-
-bits 16
-
-mov word [1000], 1
-mov word [1002], 2
-mov word [1004], 3
-mov word [1006], 4
-
-mov bx, 1000
-mov word [bx + 4], 10
-
-mov bx, word [1000]
-mov cx, word [1002]
-mov dx, word [1004]
-mov bp, word [1006]

asm_files/list-0051.txt

@@ -1,18 +0,0 @@
---- test\listing_0051_memory_mov execution ---
-mov word [+1000], 1 ; ip:0x0->0x6 
-mov word [+1002], 2 ; ip:0x6->0xc 
-mov word [+1004], 3 ; ip:0xc->0x12 
-mov word [+1006], 4 ; ip:0x12->0x18 
-mov bx, 1000 ; bx:0x0->0x3e8 ip:0x18->0x1b 
-mov word [bx+4], 10 ; ip:0x1b->0x20 
-mov bx, [+1000] ; bx:0x3e8->0x1 ip:0x20->0x24 
-mov cx, [+1002] ; cx:0x0->0x2 ip:0x24->0x28 
-mov dx, [+1004] ; dx:0x0->0xa ip:0x28->0x2c 
-mov bp, [+1006] ; bp:0x0->0x4 ip:0x2c->0x30 
-
-Final registers:
-      bx: 0x0001 (1)
-      cx: 0x0002 (2)
-      dx: 0x000a (10)
-      bp: 0x0004 (4)
-      ip: 0x0030 (48)

decoding.odin

@@ -99,13 +99,13 @@ parse_operand :: proc(inst: InstructionInfo, opinfo: OperandInfo, data: []u8, pr
                 op = (DirectAddress)(get_i16(data[2:]))
                 processed^ += 2
             } else {
-                op = MemoryAddr{ addr_id = rm }
+                op = MemoryAddr{ addr_id = rm , displacement = None{} }
             }
         } else if mod == 1 {
-            op = MemoryAddr{ addr_id = rm , displacement_value = (i16)(data[2]) , displacement_size = .Signed8 }
+            op = MemoryAddr{ addr_id = rm , displacement = (i8)(data[2]) }
             processed^ += 1
         } else if mod == 2 {
-            op = MemoryAddr{ addr_id = rm , displacement_value = get_i16(data[2:]) , displacement_size = .Signed16 }
+            op = MemoryAddr{ addr_id = rm , displacement = get_i16(data[2:]) }
             processed^ += 2
         } else if mod == 3 {
             if word {

execution.odin

@@ -11,6 +11,7 @@ get_ip :: proc(cpu: ^Cpu) -> int { return int(cpu.registers[.ip].full) }
 get_operand_value :: proc(cpu: ^Cpu, operand: Operand) -> i16 {
     #partial switch opr in operand {
     case Immediate:
+        // fmt.printfln("0x%4x %d", i16(opr.value), opr.value)
         return i16(opr.value)
     case RegisterId:
         reg_val := cpu.registers[opr.name]
@@ -20,9 +21,6 @@ get_operand_value :: proc(cpu: ^Cpu, operand: Operand) -> i16 {
         case .Full:
             return i16(reg_val.full)
         }
-    case DirectAddress:
-        value := i16(u16(cpu.memory[opr+1] << 8) | u16(cpu.memory[opr]))
-        return value
     }
     return 0
 }
@@ -109,32 +107,6 @@ execute_instruction :: proc(cpu: ^Cpu, inst: Instruction) {
             check_auxiliary_carry_flag(cpu, dst_val, src_val, false)
             check_carry_flag(cpu, dst_val, src_val, false)
         }
-    } else if addr,ok := inst.dst.(DirectAddress); ok {
-        #partial switch inst.opname {
-        case .MOV:
-            if imm,ok := inst.src.(Immediate); ok {
-                if imm.size == .Signed16 {
-                    cpu.memory[addr]   = u8(imm.value & 0x00FF)
-                    cpu.memory[addr+1] = u8((u16(imm.value) & 0xFF00) >> 8)
-                } else {
-                    cpu.memory[addr] = u8(imm.value)
-                }
-            }
-        }
-    } else if mem_addr,ok := inst.dst.(MemoryAddr); ok {
-        #partial switch inst.opname {
-        case .MOV:
-            if imm,ok := inst.src.(Immediate); ok {
-                // TODO: We need a function that returns the registers to check out
-                addr := cpu.registers[.bx].full + mem_addr.displacement_value
-                if imm.size == .Signed16 {
-                    cpu.memory[addr]   = u8(imm.value & 0x00FF)
-                    cpu.memory[addr+1] = u8((u16(imm.value) & 0xFF00) >> 8)
-                } else {
-                    cpu.memory[addr] = u8(imm.value)
-                }
-            }
-        }
     } else if jmp_offset,ok := inst.src.(Jump); ok {
         jump: bool
         #partial switch inst.opname {

printing.odin

@@ -39,10 +39,18 @@ calculate_effective_address :: proc(r_m: u8) -> string {
 
 get_memory_string :: proc(memoryAddr: MemoryAddr, has_segment: Maybe(RegisterId)) -> string {
     disp: string
-    value := memoryAddr.displacement_value
+    switch value in memoryAddr.displacement {
+    case None:
+        disp = ""
+    case Disp8:
         if value != 0 {
             disp = fmt.aprintf(" %s %d", value > 0 ? "+" : "-", math.abs(value))
         }
+    case Disp16:
+        if value != 0 {
+            disp = fmt.aprintf(" %s %d", value > 0 ? "+" : "-", math.abs(value))
+        }
+    }
     seg_string: string
     if segreg, ok := has_segment.?; ok {
         seg_string = fmt.aprintf("%s:", get_register_name(segreg))
@@ -51,6 +59,21 @@ get_memory_string :: proc(memoryAddr: MemoryAddr, has_segment: Maybe(RegisterId)
     return text
 }
 
+get_displacement_string :: proc(displacement: Displacement) -> string {
+    disp := ""
+    #partial switch value in displacement {
+    case i8:
+        if value != 0 {
+            disp = fmt.aprintf(" %s %d", value > 0 ? "+" : "-", math.abs(value))
+        }
+    case i16:
+        if value != 0 {
+            disp = fmt.aprintf(" %s %d", value > 0 ? "+" : "-", math.abs(value))
+        }
+    }
+    return disp
+}
+
 get_register_name :: proc(reg_id: RegisterId) -> string {
     low_names := [?]string{"al", "cl", "dl", "bl"}
     high_names := [?]string{"ah", "ch", "dh", "bh"}

sim8086.odin

@@ -44,7 +44,7 @@ main :: proc() {
     }
 
     cpu := Cpu {
-        memory = make([dynamic]u8, 1024 * 1024), // 1,048,576
+        memory = make([dynamic]u8, 1_048_576), // Exact num per the manual
     }
 
     execute_instructions(&cpu, decoded_insts)

types.odin

@@ -46,6 +46,13 @@ WordSize :: enum {
 }
 
 None :: struct {}
+Disp8 :: i8
+Disp16 :: i16
+Displacement :: union {
+    None,
+    Disp8,
+    Disp16
+}
 
 RegisterAccess :: enum {
     Full,
@@ -68,8 +75,7 @@ Immediate :: struct {
 }
 MemoryAddr :: struct {
     addr_id: u8,
-    displacement_value: i16,
+    displacement: Displacement,
-    displacement_size: ImmediateSize,
 }
 DirectAddress :: distinct i16
 Jump :: distinct i8