Changeset 42791 in vbox

Timestamp:

Aug 13, 2012 12:38:33 PM (12 years ago)

Author:

vboxsync

Message:

BIOS: Fixed 16-bit PM APM interface.

Location:

trunk/src/VBox/Devices/PC/BIOS

Files:

• apm.c (modified) (1 diff)
• apm_pm.asm (modified) (3 diffs)
• notes.txt (modified) (1 diff)

trunk/src/VBox/Devices/PC/BIOS/apm.c

@@ -165 +165 @@
         // @todo: change connection state
         break;
+    case APM_PM_CONN:
+        // @todo: validate device ID
+        // @todo: validate current connection state
+        // @todo: change connection state
+        AX = APM_BIOS_SEG;              /* 16-bit PM code segment (RM segment base). */
+        BX = (uint16_t)apm_pm16_entry;  /* 16-bit PM entry point offset. */
+        CX = APM_BIOS_SEG;              /* 16-bit data segment. */
+        SI = APM_BIOS_SEG_LEN;          /* 16-bit PM code segment length. */
+        DI = APM_BIOS_SEG_LEN;          /* Data segment length. */
+        break;
     case APM_32_CONN:
         // @todo: validate device ID

trunk/src/VBox/Devices/PC/BIOS/apm_pm.asm

@@ -124 +124 @@
 
 
+;; 16-bit protected mode APM entry point
+
+;; According to the APM spec, only CS (16-bit code selector) is defined.
+;; The data selector can be derived from it.
 
 apm_pm16_entry:
-                stc
-                retf                    ; return to 16-bit caller
+
+                mov     ah, 2           ; mark as originating in 16-bit PM
+                
+                                        ; fall through
 
 apm_pm16_entry_from_32:
@@ -144 +150 @@
                 pop     ds              ; restore registers
 
-.386
-                retfd                   ; return to 32-bit code
+                retf                    ; return to caller - 16-bit return
+                                        ; even to 32-bit thunk!
 
 _TEXT           ends
@@ -161 +167 @@
 ;; selector and the data selector can be derived from it.
 
+;; WARNING: To simplify matters, we use 16-bit far return to go from 32-bit
+;; code to 16-bit and back. As a consequence, the 32-bit APM code must lie
+;; below 64K boundary in the 32-bit APM code segment.
+
 apm_pm32_entry:
 
-;               cli
-;               hlt
-
                 push    ebp             ; ebp is not used by APM
 
-                push    cs              ; return address for 16-bit code
-                push    apm_pm32_back
+                mov     bp, cs          ; return address for 16-bit code
+                push    bp
+                mov     ebp, apm_pm32_back
+                push    bp              ; Note: 16:16 address!
 
                 push    cs
                 pop     ebp
                 add     ebp, 8          ; calculate 16-bit code selector
-                push    ebp             ; push 16-bit code selector
-
-                xor     ebp, ebp        ; manually pad 16-bit offset
-                push    bp              ; to a 32-bit value
-                push    apm_pm16_entry_from_32
+                push    bp              ; push 16-bit code selector
+
+                mov     ebp, apm_pm16_entry_from_32
+                push    bp              ; push 16-bit offset
 
                 mov     ah, 3           ; mark as originating in 32-bit PM
+
+                db      66h             ; force a 16-bit return
                 retf                    ; off to 16-bit code...
 

trunk/src/VBox/Devices/PC/BIOS/notes.txt

@@ -45 +45 @@
 
 - PC DOS 6.x/7.x QCONFIG is a rare user of INT 16h fn 0Ah (read keyboard ID).
+
+- DOS POWER.EXE uses the real mode APM interface, OS/2 APM.SYS uses the 16-bit
+  protected mode APM interface, and Windows 9x uses the 32-bit protected mode
+  APM interface.
 
 - Windows 98 is one of the few APM 1.2 users; Windows 95 uses APM 1.1, while