bios: commit missing file

bios/util/__call_to_ram.s

@@ -0,0 +1,79 @@
+/**
+ * Copyright (c) 2023, 2024 Adrian "asie" Siekierka
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+	.arch	i186
+	.code16
+	.intel_syntax noprefix
+
+#include "common.inc"
+
+    // Input:
+	// - DI = pointer to code
+	// - BP = size, in words
+    // Preserve AX, BX, CX, DX, SI
+    .global __call_to_ram
+__call_to_ram:
+    // Allocate stack
+    sub sp, bp
+    sub sp, bp
+    push bp
+    push cx
+    mov bp, sp
+    add bp, 4
+
+    // Copy code to RAM
+    push ds
+    push es
+    push si
+    push di
+
+    push cs
+    pop ds
+    push ss
+    pop es
+    mov si, di
+    mov di, bp
+    mov cx, [bp - 2]
+    cld
+    rep movsw
+
+    pop di
+    pop si
+    pop es
+    pop ds
+    pop cx
+
+    // Push return pointer
+    push cs
+    push offset __call_to_ram_ret
+    // Push code pointer
+    push ss
+    push bp
+    // Jump to code in RAM
+    retf
+
+__call_to_ram_ret:
+    // Restore stack
+    pop bp
+    add sp, bp
+    add sp, bp
+    ret