How to Modify VxD in VKD_Define_Hot_Key to Detect All Keys

• Microsoft Windows Device Development Kit (DDK) for Windows 95

SUMMARY

In Windows 95, the keyboard input is handled by the keyboard driver and is virtualized by the VxD called (default) VKD.VXD. At ring 0, a VxD can call VKD_Define_Hot_Key to set a call back on certain keystrokes. This may seem not to work on some key combinations or events. This article provides sample code showing how to modify the VKD source code supplied with the Windows 95 DDK to trace the hot key evaluation and see all the scan codes as they are typed. With modification, this should also work in the Windows version 3.1 DDK sample.

MORE INFORMATION

The VxDCall VKD_Define_Hot_Key uses the VMM list services to create a list of all hot keys currently set. When a key is changed (pressed or released) the routine Chk_Hot_Keys in VKDHK.ASM is called to compare it to the list.

Certain key combinations do not register as a single event, so drivers that need to detect them must keep track of the key history. The following sample code, replacing the first part of Chk_Hot_Keys, sends out the exact scan code and shift state for reference on every key event as well as advisory messages as to hot key detection.

The code was tested by building in the SDK95/DDK95/MASM6.11 environment, using WDEB386 as the debugger. Note the use of conditional trace outs. Remember also, that you will most likely be calling VKD_Reflect_Hot_Key ("I am not doing anything with this key now but pass it on") or VKD_Cancel_Hot_Key ("I have handled this key - no further system action") as part of your call back routine.

Sample Code

BeginProc Chk_Hot_Keys

;!!! key trace

   trace_out "Chk_Hot_Keys key #AX"

   VK_HK_Queue_Out "Chk_Hot_Keys key scan code = #AX ..."

   push  eax

   mov   eax,[vkd_gbl_shift_state]
   trace_out "Chk_Hot_Keys ... shift state = #AX"
   pop   eax
   push  eax

   test  [VKD_gbl_shift_state], SS_Shift_mask + SS_Toggle_Dn_mask
                   ;Q: are any shift state keys down?

   trace_outNZ "---------- Shift State keys DOWN"

   jnz   short chkhk_1         ; Y:
   and   eax, (NOT SC_Break AND 0FFh) OR VK_Extended
                   ; clear all but Extended bit &
                   ; base scan code

   cmp   eax, Pause_HK         ;Q: special single key hot key?

   trace_outZ "---------- NO CHECK performed (special key)"

   jz DEBFAR je_don_t_check       ; N: (chained short jumps)

   mov   eax, [esp]         ; retrieve saved eax value

   push  ebx
   mov   ebx, [esp+8]
   VK_HK_Queue_Out 'Chk_Hot_Keys #ax, called from ?ebx'
   pop   ebx

   test  al, SC_Break          ;Q: key being released?
   jz short continue_check
   TestMem [VKD_flags], VKDf_HK_hold   ;Q: already in hot key state?

   je DEBFAR don_t_check       ; N: don't enter hot key state
                   ;    on just the release!

   trace_out "---------- CHECK performed"

   pushad
   mov   edi, esi        ; point edi at CB data
   mov   cx, ax             ; save virtual key
   mov   esi, [Hot_Key_List]
   VMMCall List_Get_First
   jz short no_hot_keys     ; jump if no hot keys defined

;

   and   cx, VK_Extended + (0FFh XOR SC_Break)

chk_key:

   cmp   cl, [eax.Hot_Key_scan_code] ;Q: scan codes match?
   jne   short no_key          ; N:
   cmp   [eax.Hot_Key_extended], AllowExtended_B ;Q: ignore extended flag?
   je short accept_key      ;        Y:
   cmp   ch, [eax.Hot_Key_extended]  ;Q: same ext status?
   jne   short no_key          ; N:

   mov   ebx, [VKD_gbl_shift_state]
   and   bx, [eax.Hot_Key_SS_Mask]
   cmp   bx, [eax.Hot_Key_SS_Compare] ;Q: correct shift state?
   je short hot_key_fnd     ; Y:

   VMMCall List_Get_Next          ; EAX is next key definition
   jnz   chk_key

   clc                ; failed!
   jmp   short chk_exit

   trace_out "---------- HOT KEY found! = #EAX"

   VK_HK_Queue_Out "Chk_Hot_Keys Hot key detected #eax"

   mov   ebx, [eax.Hot_Key_Local_Flag]
   bt [edi.disabled_hot_keys], ebx ;Q: key disabled?
   jnc   short hot_not_disabled      ; N: match found

   test  byte ptr [esp.Pushad_EAX], SC_Break ;Q: release hot key?

   jnz   SHORT D00_handle_up_on_disabled
   VK_HK_Queue_Out "Chk_Hot_Keys Hot key disabled"
   jmp   no_key

   jz no_key

   and   [eax.Hot_Key_call_mask], NOT Hot_Key_Down   ; flag as key up
   mov   bl, byte ptr [esp.Pushad_EAX]
   mov   [VKD_last_key], bl
   jmp   no_key

   TestMem  [eax.Hot_Key_call_mask], Monitor_Key ; monitoring only?
   jnz   Hot_Key_Activate_Monitor    ; Y: Handle internally
   stc
   mov   [esp.Pushad_EBX], eax       ; return handle of hot key

   popad

   pop   eax
   ret

REFERENCES

Windows 95 DDK sample code in KEYB\SAMPLES\VKD related sample in KEYB\SAMPLES\VKXD