Pass INT 13h results back to the caller

Also removed some debugging NOPs.
MobyGamer · Dec 6, 2022 · 431b8f8 · 431b8f8
1 parent efbc442
commit 431b8f8
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Showing 2 changed files with 18 additions and 7 deletions.
diff --git a/README.md b/README.md
@@ -77,3 +77,5 @@ Information on determining PC vs. AT 8255 from Kris Heidenstrom (RIP).
 Methodology for detecting video hardware adapted from Richard Wilton.
 
 Greetz to VileR, who drew a CGA mode4+mode6 "LED" bitmap on short notice :-)
+
+Thanks to E. C. Masloch for bringing attention to a potentially fatal bug.
diff --git a/SOFTHDDI.ASM b/SOFTHDDI.ASM
@@ -540,7 +540,6 @@ IF NOBIOSMODE
         call    draw_mode4
         pop     di
 ENDIF
-        nop
         inc     di                      ;first char attribute is at offset 1
 IF REMOVESNOW
         cmp     [vidcard],h_CGA         ;hold up, is this a real CGA card?
@@ -604,7 +603,6 @@ IF NOBIOSMODE
         call    eras_mode4
         pop     di
 ENDIF
-        nop
         inc     di                      ;first char attribute is at offset 1
         mov     ax,[word ptr oldVTXT]   ;retrieve what we need to restore
 IF REMOVESNOW
@@ -866,16 +864,27 @@ ISP_HEADER 13h
 doindicators:
         pop     bx                      ;restore changed bx
         call    diskIntEnter            ;start indicators
-        ;Simulate interrupt call to original INT 13h
-        ;pushf                          ;not needed, orig. flags already pushed
+        popf                            ;restore flags from entrypoint
+        pushf                           ;simulate INT call
         call    ORIG_INT13h             ;pass to original disk interrupt
-        pushf                           ;save int13 result flags
+        pushf                           ;save INT 13h result flags
         call    diskIntLeave            ;stop indicators
-        popf                            ;restore int13 result flags
+        popf                            ;restore INT 13h result flags
+        ;To pass the results as if they were ours, patch them into stack frame
+        push    bp
+        mov     bp,sp                   ;bp+0 = saved bp
+                                        ;bp+2 = ip
+                                        ;bp+4 = cs
+                                        ;bp+6 = flags
+        push    ax
+        lahf                            ;ah = flags
+        mov     byte ptr [bp+6],ah      ;patch flags into stack frame
+        pop     ax
+        pop     bp
         iret                            ;leave int13
 noindicators:
         pop     bx                      ;restore potentially-changed bx
-        popf                            ;restore flags from entry
+        popf                            ;restore flags from entrypoint
         jmp     ORIG_INT13h
 
 resident_code_size equ offset $