From 52be99d8c0862ff87db9a4f9ccec1ac4b5f7caed Mon Sep 17 00:00:00 2001
From: Andreas Baumann <mail@andreasbaumann.cc>
Date: Fri, 2 Sep 2022 09:18:52 +0200
Subject: added a quite unsorted first version of a floppy boot loader

---
 floppy/tests/test_a20.asm    | 61 ++++++++++++++++++++++++++++++++++++++++++++
 floppy/tests/test_unreal.asm | 49 +++++++++++++++++++++++++++++++++++
 2 files changed, 110 insertions(+)
 create mode 100644 floppy/tests/test_a20.asm
 create mode 100644 floppy/tests/test_unreal.asm

(limited to 'floppy/tests')

diff --git a/floppy/tests/test_a20.asm b/floppy/tests/test_a20.asm
new file mode 100644
index 0000000..43da6e3
--- /dev/null
+++ b/floppy/tests/test_a20.asm
@@ -0,0 +1,61 @@
+; The following code is public domain licensed
+ 
+[bits 16]
+ 
+; Function: check_a20
+;
+; Purpose: to check the status of the a20 line in a completely self-contained state-preserving way.
+;          The function can be modified as necessary by removing push's at the beginning and their
+;          respective pop's at the end if complete self-containment is not required.
+;
+; Returns: 0 in ax if the a20 line is disabled (memory wraps around)
+;          1 in ax if the a20 line is enabled (memory does not wrap around)
+ 
+check_a20:
+    pushf
+    push ds
+    push es
+    push di
+    push si
+ 
+    cli
+ 
+    xor ax, ax ; ax = 0
+    mov es, ax
+ 
+    not ax ; ax = 0xFFFF
+    mov ds, ax
+ 
+    mov di, 0x0500
+    mov si, 0x0510
+ 
+    mov al, byte [es:di]
+    push ax
+ 
+    mov al, byte [ds:si]
+    push ax
+ 
+    mov byte [es:di], 0x00
+    mov byte [ds:si], 0xFF
+ 
+    cmp byte [es:di], 0xFF
+ 
+    pop ax
+    mov byte [ds:si], al
+ 
+    pop ax
+    mov byte [es:di], al
+ 
+    mov ax, 0
+    je check_a20__exit
+ 
+    mov ax, 1
+ 
+check_a20__exit:
+    pop si
+    pop di
+    pop es
+    pop ds
+    popf
+ 
+    ret
diff --git a/floppy/tests/test_unreal.asm b/floppy/tests/test_unreal.asm
new file mode 100644
index 0000000..687a528
--- /dev/null
+++ b/floppy/tests/test_unreal.asm
@@ -0,0 +1,49 @@
+; Assembly example
+ 
+; nasm boot.asm -o boot.bin
+; partcopy boot.bin 0 200 -f0
+ 
+[ORG 0x7c00]              ; add to offsets
+ 
+start:   xor ax, ax       ; make it zero
+   mov ds, ax             ; DS=0
+   mov ss, ax             ; stack starts at seg 0
+   mov sp, 0x9c00         ; 2000h past code start, 
+                          ; making the stack 7.5k in size
+ 
+   cli                    ; no interrupts
+   push ds                ; save real mode
+ 
+   lgdt [gdtinfo]         ; load gdt register
+ 
+   mov  eax, cr0          ; switch to pmode by
+   or al,1                ; set pmode bit
+   mov  cr0, eax
+ 
+   jmp $+2                ; tell 386/486 to not crash
+ 
+   mov  bx, 0x08          ; select descriptor 1
+   mov  ds, bx            ; 8h = 1000b
+ 
+   and al,0xFE            ; back to realmode
+   mov  cr0, eax          ; by toggling bit again
+ 
+   pop ds                 ; get back old segment
+   sti
+ 
+   mov bx, 0x0f01         ; attrib/char of smiley
+   mov eax, 0x0b8000      ; note 32 bit offset
+   mov word [ds:eax], bx
+ 
+   jmp $                  ; loop forever
+ 
+gdtinfo:
+   dw gdt_end - gdt - 1   ;last byte in table
+   dd gdt                 ;start of table
+ 
+gdt         dd 0,0        ; entry 0 is always unused
+flatdesc    db 0xff, 0xff, 0, 0, 0, 10010010b, 11001111b, 0
+gdt_end:
+ 
+   times 510-($-$$) db 0  ; fill sector w/ 0's
+   dw 0xAA55              ; Required by some BIOSes
-- 
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