rmtrap.asm: register ax pushed/popped for port 0x20 trapping

Author: Baron-von-Riedesel

src/PTRAP.C

@@ -231,6 +231,7 @@ bool PTRAP_Prepare_RM_PortTrap()
 #if !RMPICTRAPDYN
     DPMI_CopyLinear( dosmem + 8, DPMI_PTR2L(&QPI_Entry), 4 );
 #endif
+    /* 4+4+4 are sizes of variables in RMWRAP.ASM */
     DPMI_CopyLinear( dosmem + 4 + 4 + 4, DPMI_PTR2L( &PTRAP_RM_Wrapper ), &PTRAP_RM_WrapperEnd - &PTRAP_RM_Wrapper );
 
     /* set new trap handler ES:DI */
@@ -292,6 +293,10 @@ bool PTRAP_Install_RM_PortTraps( void )
     return true;
 }
 
+/* set PIC port trap when a SB IRQ is emulated.
+ * Since the SB IRQ is emulated, no EOI must be sent to the PIC.
+ */
+
 void PTRAP_SetPICPortTrap( int bSet )
 /////////////////////////////////////
 {
@@ -312,7 +317,8 @@ void PTRAP_SetPICPortTrap( int bSet )
         DPMI_CallRealModeRETF(&r); /* trap port */
 #else
         /* patch the 16-bit real-mode code stored in the PSP.
-         * see rmwrap.asm, proc PTRAP_RM_Wrapper
+         * see rmwrap.asm, proc PTRAP_RM_Wrapper.
+         * the +12 is the size of variables in RMWRAP.ASM!
          */
         uint32_t dosmem = _go32_info_block.linear_address_of_original_psp + 0x80;
         if ( bSet ) {

src/RMWRAP.ASM

@@ -10,20 +10,26 @@
 
 	.errnz __JWASM__ lt 218,<JWasm v2.18+ required>
 
-HANDLE_IN_388H_DIRECTLY equ 1 ; must match #define in ptrap.c
-RMPICTRAPDYN            equ 0 ; must match #define in ptrap.c
+HANDLE_IN_388H_DIRECTLY equ 1 ; std=1, must match #define in ptrap.c
+RMPICTRAPDYN            equ 0 ; std=0, must match #define in ptrap.c
+
+;--- if RMPICTRAPDYN is 0, the PIC port 0020h is permanently trapped.
+;--- if RMPICTRAPDYN is 1, the PIC port 0020h is trapped only while an IRQ 5/7
+;--- is emulated. This is quite some overhead, currently unsure if it works stable.
 
 	.code
 
 	assume ds:nothing, ss:nothing
 
+;--- 12 bytes data - if this is changed, PTRAP.C must be adjusted!
 _0000 dd 0	; rmcb to vsbhda port trap handler
-_0004 db 0 
+_0004 db 0	; last 388h value written
 _0005 db 0
-      dw 0
-_0008 dd 0	; entry Jemm/Qemm "untrapped io"
+      dw 0	; not used
+_0008 dd 0	; QPI entry Jemm/Qemm, for "untrapped io"
 
-;--- port trap proc, called by Jemm/Qemm
+;--- port trap proc, called by QPIEmu/Qemm;
+;--- this code runs in real-mode.
 
 PTRAP_RM_Wrapper proc c public
 
@@ -42,7 +48,7 @@ normal:
 is388:
 	test cl, 4			; OUT instr?
 	jnz is388out
-	mov al, [_0005]		; IN 388h
+	mov al, [_0005]		; last timer value written to 389h
 	test al, 1
 	jz @F
 	mov al, 0C0h
@@ -68,19 +74,22 @@ is389:
 endif
 
 ife RMPICTRAPDYN
+
+;--- this code runs when NO IRQ 5/7 is emulated.
+;--- since port 0020h is permanently trapped, QPI must be called
+;--- to execute the IN/OUT instruction.
+;--- 02/2024: fixed: register AH/AX preserved for IN/OUT
+
 is20:
 	push bx
+	xchg ax, bx
 	test cl, 4			; OUT instr?
-	jnz is20out
-	mov ax, 1a00h
-	call [_0008]  
-	mov al, bl
-	pop bx
-	retf
-is20out:
-	mov bl, al
-	mov ax, 1a01h
-	call [_0008]
+	.386
+	setnz al			; ax=1a00h is "sim IN", 1a01h = "sim OUT"
+	.286
+	mov ah, 1ah
+	call [_0008]		; call QPIEmu/Qemm
+	xchg ax, bx
 	pop bx
 	retf
 endif