5 files changed, 66 insertions, 17 deletions
diff --git a/atk16_asm/asm_pass0.py b/atk16_asm/asm_pass0.py
index b30ddc0..270dc7a 100644
--- a/atk16_asm/asm_pass0.py
+++ b/atk16_asm/asm_pass0.py
@@ -1,5 +1,6 @@
 from dataclasses import dataclass
 import os.path
+from typing import Callable
 from .asm_ops import *
 from .asm_eval import *
 from .tokenizer import *
@@ -14,10 +15,38 @@ class Result0Line:
 class Result0:
   lines: list[Result0Line]
 
-def pass_0(lines: list[str], file_name: str) -> Result0:
+InsertAtDataSegment = Callable[[str, str, str, int], None]
+
+def pass_0(lines: list[str], file_name: str, insert_at_data_segment: InsertAtDataSegment | None = None) -> Result0:
   file_name = file_name if file_name.endswith(".atk16") else file_name + ".atk16"
   result_lines: list[Result0Line] = []
 
+  if not insert_at_data_segment:
+    def _insert_at_data_segment(label: str, value: str, context_file_name: str, context_line_num: int):
+      data_segment_index = None
+      for idx, result_line in enumerate(result_lines):
+        if result_line.line == "%%data_segment":
+          data_segment_index = idx
+          break
+
+      if data_segment_index is None:
+        raise Exception(f"Error: @data before @data_segment in {context_file_name}:{context_line_num}")
+
+      # Inverted order because of insert semantics
+      result_lines.insert(data_segment_index + 1, Result0Line(
+        src_file=context_file_name,
+        line_num=context_line_num,
+        line=f"${{{value}}}"
+      ))
+
+      result_lines.insert(data_segment_index + 1, Result0Line(
+        src_file=context_file_name,
+        line_num=context_line_num,
+        line=f"@label {label}"
+      ))
+
+    insert_at_data_segment = _insert_at_data_segment
+
   for (line_num, line) in enumerate(lines):
     line_num += 1 # line numbers are 1-based
 
@@ -27,6 +56,23 @@ def pass_0(lines: list[str], file_name: str) -> Result0:
     keyword, *args = tokenize(line)
 
     match keyword:
+      case "@data_segment":
+        data_segment_sentinel = "%%data_segment"
+        result_lines.append(Result0Line(
+          src_file=file_name,
+          line_num=line_num,
+          line=data_segment_sentinel
+        ))
+
+      case "@data":
+        if len(args) != 2:
+          raise Exception(f"Error: @data missing arguments in {file_name}:{line_num}")
+
+        name = args[0]
+        data = args[1]
+
+        insert_at_data_segment(name, data, file_name, line_num)
+
       case "@include":
         asm_file_name = args[0] if args[0].endswith(".atk16") else args[0] + ".atk16"
         # if starts with %, use the path relative to this source file, not the current working directory
@@ -40,7 +86,7 @@ def pass_0(lines: list[str], file_name: str) -> Result0:
         with open(path, "r") as f:
           incl_lines = f.readlines()
 
-        incl_result0 = pass_0(incl_lines, asm_file_name)
+        incl_result0 = pass_0(incl_lines, asm_file_name, insert_at_data_segment)
         for incl_line in incl_result0.lines:
           result_lines.append(Result0Line(
             src_file=incl_line.src_file,
diff --git a/atk16_asm/asm_pass1.py b/atk16_asm/asm_pass1.py
index 4786afa..d192b5e 100644
--- a/atk16_asm/asm_pass1.py
+++ b/atk16_asm/asm_pass1.py
@@ -35,6 +35,9 @@ def pass_1(result0: Result0) -> Result1:
           expansion = mod_expansions[op]
           if ops == "*" or op in ops_split:
             operations[op] = expansion
+      case "%%data_segment":
+        # drop the data_segment sentinel
+        continue
       case _:
         result_lines.append(Result1Line(
           src_file=line.src_file,
diff --git a/atk16_asm/builtin_asm/bootstrap.atk16 b/atk16_asm/builtin_asm/bootstrap.atk16
index 28d8aa1..b3b4254 100644
--- a/atk16_asm/builtin_asm/bootstrap.atk16
+++ b/atk16_asm/builtin_asm/bootstrap.atk16
@@ -31,10 +31,10 @@
 @let vt_text_mem     0x19 ; Text memory buffer address
 
 @address vector_table
-  hlt_isr        ; 0x10
-  hlt_isr        ; 0x11
-  hlt_isr        ; 0x12
-  hlt_isr        ; 0x13
+  no_op_isr      ; 0x10
+  no_op_isr      ; 0x11
+  no_op_isr      ; 0x12
+  no_op_isr      ; 0x13
   stack_segment  ; 0x14
   terminal_addr  ; 0x15
   keyboard_addr  ; 0x16
@@ -42,9 +42,13 @@
   sprite_mem     ; 0x18
   text_mem       ; 0x19
 
-@label hlt_isr
-  ldi 0x55 RE
-  hlt
+@label no_op_isr
+  rti
+
+; Define data segment location to this address
+; Programs can use `@data label value` to inject data here
+@label data_segment
+@data_segment
 
 ; Example ISR for keyboard to terminal
 ; @label keyboard_to_terminal_isr
diff --git a/atk16_asm/builtin_asm/std_bump_alloc.atk16 b/atk16_asm/builtin_asm/std_bump_alloc.atk16
index 1d87435..32516bc 100644
--- a/atk16_asm/builtin_asm/std_bump_alloc.atk16
+++ b/atk16_asm/builtin_asm/std_bump_alloc.atk16
@@ -21,10 +21,8 @@
 ; The alloc_next value is a pointer to the next free word in the heap.
 ; It is stored in the first word of the heap.
 
-@label bump_next_p
-  heap_segment
-@label bump_arena_start
-  ${heap_segment - 1}
+@data bump_next_p heap_segment
+@data bump_arena_start ${heap_segment - 1}
 
 @label bump_reset
   ; reset the heap to its initial state (zero allocated blocks)
diff --git a/atk16_asm/builtin_asm/std_math.atk16 b/atk16_asm/builtin_asm/std_math.atk16
index 58b9cdb..6544b32 100644
--- a/atk16_asm/builtin_asm/std_math.atk16
+++ b/atk16_asm/builtin_asm/std_math.atk16
@@ -1,7 +1,5 @@
-@label mul_sign_mask
-  ${2 ** 15}
-@label mul_not_mask
-  0xFFFF
+@data mul_sign_mask ${2 ** 15}
+@data mul_not_mask 0xFFFF
 
 @label mul
   ; multiply a signed (a) and a signed (b)