From d7f4049849e14bfe244c040e97126afb234378c5 Mon Sep 17 00:00:00 2001
From: crazii <crazii.he@yahoo.com>
Date: Mon, 18 May 2026 13:19:13 +0800
Subject: [PATCH] fix int08 stack for DPMI mode.

---
 iss_tim.pas | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/iss_tim.pas b/iss_tim.pas
index 1d7ac8e..40bd993 100644
--- a/iss_tim.pas
+++ b/iss_tim.pas
@@ -61,6 +61,8 @@
 
 Implementation
 
+Var IntStack        : array[0..4095] of byte;
+
 Var TimerSpeed      : DWord;
     OldTimer        : TSegInfo;
     OldTimerCnt     : DWord;
@@ -96,7 +98,16 @@
   PUSH   FS
   PUSH   GS
   PUSHAD
+
+  { with DPMI, the stack is not DS/ES, but a minimal 4K locked pm stack dedicated for interrupts, switch to DS }
+  MOV    CX, SS
+  MOV    EDX, ESP
   MOV    AX,CS:[BackupDS]
+  MOV    SS, AX
+  LEA    ESP, IntStack+4096
+  PUSH   CX
+  PUSH   EDX
+
   MOV    DS,AX
   MOV    ES,AX
   MOV    AX,DosMemSelector
@@ -129,6 +140,13 @@
   MOV   DX,$20 { þ Interrupt request acknowledge þ }
   MOV   AL,$20
   OUT   DX,AL
+
+  {restore old stack}
+  POP   EDX
+  POP   CX
+  MOV   SS, CX
+  MOV   ESP, EDX
+
   POPAD
   POP   GS
   POP   FS