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--- back2root:ibm-pc-ms-dos:interrupts:int_21:int_21_34 [2023/01/10 11:55] – supprimée - modification externe (Unknown date) 127.0.0.1
+++ back2root:ibm-pc-ms-dos:interrupts:int_21:int_21_34 [2024/04/08 08:23] (Version actuelle) – ↷ Liens modifiés en raison d'un déplacement. 23.22.35.162
@@ Ligne 1: / Ligne 1: @@
+====== INT 0x21 - 0x34 - Get Address to DOS Critical Flag ======
+<WRAP round info >
+INDOS (Undocumented DOS 2.0+)
+</WRAP>
+===== Request/Call: =====
+{{tablelayout?rowsHeaderSource=Auto&colwidth=""}}
+^  reg  ^  value  ^  descr  ^
+|  AH   |  0x34   |         |
+===== Return: =====
+{{tablelayout?rowsHeaderSource=Auto&colwidth=""}}
+^  reg  ^   descr  ^
+|  ES:BX  | address of a byte indicating whether a DOS call is in progress. No DOS calls should be made if set.  |
+===== Notes & Comments =====
+<WRAP round box>
+  * AKA the INDOS flag, this critical section flag may be checked from within an interrupt handler before requesting a DOS service. It is a semaphore that is non-zero when DOS is busy, and zero otherwise.
+  * though this flag indicates whether a DOS interrupt is active, it should not be used alone to determine DOS is safe for re-entry; Here's the standard rule for safe DOS entry: if [[back2root:ibm-pc-ms-dos:interrupts:int_28:start|INT 28]] is active or this flag and the critical error flag are clear then it is safe to call DOS
+  * this interrupt should be used only during TSR initialization; the returned pointer should be used thereafter
+  * this flag is cleared after a critical error ([[back2root:ibm-pc-ms-dos:interrupts:int_24|INT 24]])
+    * ES:BX-1 points to the critical error flag for DOS 3.x+
+    * ES:BX+1 points to the critical error flag for DOS 2.x
+    * ES:BX-1AA points to the critical error flag for COMPAQ DOS 3.0
+INT [[back2root:ibm-pc-ms-dos:interrupts:int_21_5d|21,5D]] in DOS 3.x+ can be used to locate the critical error flag</WRAP>
+[[start|Back]]

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