From 9493cf35a2986c6d9f043aa7eac3afe4d36e95a7 Mon Sep 17 00:00:00 2001
From: Jeffrey Armstrong <jeff@approximatrix.com>
Date: Sat, 16 Nov 2024 13:46:46 -0500
Subject: Added code to detect OS version mostly through MS-DOS interrupt
 calls.

---
 asm/dosver.asm | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 asm/dosver.asm

(limited to 'asm')

diff --git a/asm/dosver.asm b/asm/dosver.asm
new file mode 100644
index 0000000..8406663
--- /dev/null
+++ b/asm/dosver.asm
@@ -0,0 +1,76 @@
+        push bp
+        mov bp, sp
+        
+        mov al, 0
+        mov ah, 0x30
+        
+        int 0x21
+        
+        ; Push actual version info onto stack
+        push ax
+        
+        cmp bh, 0x00
+        jne notdrdos
+        
+        ; Check if it is DR_DOS lying about being PC_DOS
+        mov ax, 0x4452
+        int 0x21
+        jc notdrdos
+        
+        ; Mark drdos as 0xee
+        mov bh, 0xee
+        
+        ; clear the stack in a meaningless way
+        pop cx
+        
+        ; DrDos version, or something like it, is already in the ax reggy
+        jmp alldone
+        
+        
+notdrdos:
+        ; pop the actual version into ax now that we're done
+        ; with drdos checks
+        pop ax
+        
+        cmp al, 5
+        je five
+        
+        ; if al is still zero, it's dos 1
+        cmp al, 0
+        jne alldone
+        
+        ; Mark it as MS-DOS 1.0
+        mov al, 1
+        mov ah, 0
+        mov bh, 0xFF
+        jmp alldone
+        
+five:
+        ; Store the OEM version
+        push bx
+        
+        mov ax, 0x3306
+        int 0x21
+        
+        ; True version should have been in bx
+        push bx
+        pop ax
+        pop bx
+        
+alldone:
+        
+        mov cl, 8
+        shr bx, cl
+        xor bh, bh
+        
+        ; second argument - OEM code in high byte
+        mov di, [bp]+6
+        mov [di], bx
+        
+        ; first argument - major (al) minor(ah) versions
+        mov di, [bp]+8
+        mov [di], ax
+        
+        pop bp
+        retf 4
+        
\ No newline at end of file
-- 
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