From c315aab1136bbdb046ac0b278afeaad82438d743 Mon Sep 17 00:00:00 2001
From: Corwin Kuiper <corwin@kuiper.dev>
Date: Tue, 13 Apr 2021 01:32:40 +0100
Subject: [PATCH] copy iwram section to iwram

---
 crt0.s | 12 ++++++++++++
 gba.ld | 18 ++++++++++++++----
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/crt0.s b/crt0.s
index 124d95f3..73d5efeb 100644
--- a/crt0.s
+++ b/crt0.s
@@ -12,6 +12,18 @@ __start:
     ldr r1, =0x03007FFC
     str r0, [r1]
 
+
+    @ copies iwram section in rom to iwram in ram
+    ldr r0, =__iwram_rom_start              @ load memory address storing start of data for iwram in rom
+    ldr r1, =__iwram_data_start             @ load memory address storing location of iwram in ram
+    ldr r2, =__iwram_rom_length_halfwords   @ load number of 16 bit values to copy
+    swi 0x000B0000                          @ call interrupt CpuSet.
+                                            @   r0: source
+                                            @   r1: destination
+                                            @   r2: length + size information
+                                            @
+                                            @ see: https://mgba-emu.github.io/gbatek/#swi-0bh-gbands7nds9dsi7dsi9---cpuset
+
     @ load main and branch
     ldr r0, =main
     bx  r0
diff --git a/gba.ld b/gba.ld
index c5b5f3ea..526e42d1 100644
--- a/gba.ld
+++ b/gba.ld
@@ -30,18 +30,28 @@ SECTIONS {
         . = ALIGN(4);
     } > rom
 
-    __data_start = .;
-    .data : {
+    __iwram_rom_start = .;
+    .iwram : {
+        __iwram_data_start = ABSOLUTE(.);
+
         *(.data .data.*);
         . = ALIGN(4);
-    } > iwram
-    __data_end = .;
+
+        *(.text_iwram .text_iwram.*);
+        . = ALIGN(4);
+
+        __iwram_data_end = ABSOLUTE(.);
+    } > iwram AT>rom
+    
 
     .bss : {
         *(.bss .bss.*);
         . = ALIGN(4);
     } > iwram
 
+    __iwram_rom_length_bytes = __iwram_data_end - __iwram_data_start;
+    __iwram_rom_length_halfwords = (__iwram_rom_length_bytes + 1) / 2;
+
     /* discard anything not already mentioned */
     /DISCARD/ : { *(*) }
 }
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