added video bios vector detection and attempt to initialize it if it's

missing

diff --git a/efitest.asm b/efitest.asm
index 0feb61d..3ca78d0 100644 (file)
--- a/efitest.asm
+++ b/efitest.asm
@@ -138,6 +138,29 @@ start16:
 
        call print_ivt
 
+detect_vbios:
+       ; make sure we have video bios vector installed in 10h
+       mov ax, [10h * 4 + 2]
+       test ax, ax
+       jnz .notnull
+       call init_vbios
+       jnc vbios_present
+       jmp halt
+.notnull: ; beyond being non-zero, the video bios should really be at c0000h
+       cmp ax, 0c000h
+       jz vbios_present
+       ; unexpected address, make sure it starts with 0aa55h
+       mov es, ax
+       xor bx, bx
+       mov ax, [es:bx]
+       cmp ax, 0aa55h
+       call init_vbios ; seems like garbage, try init
+       jc halt
+
+vbios_present:
+       mov si, msg_vbios_test
+       call ser_putstr
+
        ; run 16bit video bios test
        mov ax, 13h
        int 10h
@@ -175,8 +198,40 @@ start16:
        jnz .yloop
 
        ; halt for ever
-.hang: hlt
-       jmp .hang
+halt:  hlt
+       jmp halt
+
+init_vbios:
+       mov ax, 0c000h
+       mov es, ax
+       xor bx, bx
+       cmp word [es:bx], 0aa55h
+       jz .foundsig
+       mov si, err_vbios_notfound
+       call ser_putstr
+       mov ax, [es:bx]
+       call printhex16
+       mov al, 13
+       call ser_putchar
+       mov al, 10
+       call ser_putchar
+       stc
+       ret
+.foundsig:
+       mov si, msg_vbios_init
+       call ser_putstr
+       ; don't bother with CRC, just call it
+       push es
+       push word 4
+       mov bp, sp
+       call far [bp]
+       add sp, 4
+       clc
+       ret
+
+msg_vbios_test db 'running video BIOS test',13,10,0
+msg_vbios_init db 'attempting to initialize video BIOS',13,10,0
+err_vbios_notfound db 'failed to initialize video BIOS, sig not found at c0000h: ',0
 
 print_ivt:
        xor bx, bx
@@ -197,7 +252,7 @@ print_ivt:
        call ser_putchar
        add bx, 4
 
-       cmp bx, 64 << 2
+       cmp bx, 33 << 2
        jnz .loop
        ret