support for using ewram

crt0.s

@@ -24,6 +24,12 @@ __start:
                                             @
                                             @ see: https://mgba-emu.github.io/gbatek/#swi-0bh-gbands7nds9dsi7dsi9---cpuset
 
+    @ copies ewram section in rom to ewram in ram
+    ldr r0, =__ewram_rom_start
+    ldr r1, =__ewram_data_start
+    ldr r2, =__ewram_rom_length_halfwords
+    swi 0x000B0000
+
     @ load main and branch
     ldr r0, =main
     bx  r0

gba.ld

@@ -43,6 +43,17 @@ SECTIONS {
         __iwram_data_end = ABSOLUTE(.);
     } > iwram AT>rom
 
+    . = __iwram_rom_start + (__iwram_data_end - __iwram_data_start);
+
+    __ewram_rom_start = .;
+    .ewram : {
+        __ewram_data_start = ABSOLUTE(.);
+
+        *(.ewram .ewram.*);
+        . = ALIGN(4);
+
+        __ewram_data_end = ABSOLUTE(.);
+    } > ewram AT>rom
     
     .bss : {
         *(.bss .bss.*);
@@ -52,6 +63,9 @@ SECTIONS {
     __iwram_rom_length_bytes = __iwram_data_end - __iwram_data_start;
     __iwram_rom_length_halfwords = (__iwram_rom_length_bytes + 1) / 2;
 
+    __ewram_rom_length_bytes = __ewram_data_end - __ewram_data_start;
+    __ewram_rom_length_halfwords = (__ewram_rom_length_bytes + 1) / 2;
+
     /* discard anything not already mentioned */
     /DISCARD/ : { *(*) }
 }

src/lib.rs

@@ -122,20 +122,38 @@ pub extern "C" fn main() -> ! {
     loop {}
 }
 
-#[test_case]
-fn trivial_test(_gba: &mut Gba) {
-    assert_eq!(1, 1);
-}
+#[cfg(test)]
+mod test {
+    use super::Gba;
 
-#[test_case]
-fn wait_30_frames(gba: &mut Gba) {
-    let vblank = gba.display.vblank.get();
-    let mut counter = 0;
-    loop {
-        if counter > 30 {
-            break;
+    #[test_case]
+    fn trivial_test(_gba: &mut Gba) {
+        assert_eq!(1, 1);
+    }
+
+    #[test_case]
+    fn wait_30_frames(gba: &mut Gba) {
+        let vblank = gba.display.vblank.get();
+        let mut counter = 0;
+        loop {
+            if counter > 30 {
+                break;
+            }
+            vblank.wait_for_VBlank();
+            counter += 1
+        }
+    }
+
+    #[link_section = ".ewram"]
+    static mut EWRAM_TEST: u32 = 5;
+    #[test_case]
+    fn ewram_static_test(_gba: &mut Gba) {
+        unsafe {
+            let content = (&EWRAM_TEST as *const u32).read_volatile();
+            assert_eq!(content, 5, "expected data in ewram to be 5");
+            (&mut EWRAM_TEST as *mut u32).write_volatile(content + 1);
+            let content = (&EWRAM_TEST as *const u32).read_volatile();
+            assert_eq!(content, 6, "expected data to have increased by one")
         }
-        vblank.wait_for_VBlank();
-        counter += 1
     }
 }