1 files changed, 23 insertions, 0 deletions
diff --git a/atk16_schasm/bootstrap.scm b/atk16_schasm/bootstrap.scm
new file mode 100644
index 0000000..09bfbb9
--- /dev/null
+++ b/atk16_schasm/bootstrap.scm
@@ -0,0 +1,23 @@
+(define addr-segment-heap       #x8000) ; grows up until SP
+(define addr-segment-mmio       #xE7F0)
+(define addr-segment-sprite     #xE800)
+(define addr-segment-text       #xF800)
+;; note: sprite memory & text memory can overlap
+;; since they are never used at the same time
+(define addr-mmio-terminal      (+ addr-segment-mmio 0))
+(define addr-mmio-keyboard      (+ addr-segment-mmio 1))
+(define addr-mmio-graphics-mode (+ addr-segment-mmio 2))
+
+(define graphics-disabled 0)
+(define graphics-text     1)
+(define graphics-sprite   2)
+
+(at-addr #x0)
+(def-label 'entrypoint
+  ;; Set stack pointer to end of heap segment, i.e. one below addr-segment-mmio.
+  ;; Stack grows down.
+  ;; Heap grows up from addr-segment-heap until it meets the stack.
+  (ld SP (u16 (- addr-segment-mmio 1)))
+  ;; Set graphics mode to disabled.
+  (ld R0 (u16 addr-mmio-graphics-mode))
+  (st R0 (u16 graphics-disabled)))