Higher confidence in the harmlessness of the ADV code

Make more sure that the ADV code is harmless when the current
derivative doesn't support it.

diff --git a/adv.inc b/adv.inc
index 0386951..7eca4b5 100644 (file)
--- a/adv.inc
+++ b/adv.inc
@@ -298,11 +298,15 @@ adv_write:
                je .bad
                cmp dword [ADVSec1],0
                je .bad
+               cmp byte [ADVDrive],-1
+               je .bad
+
                push ax
                call adv_cleanup
                mov ah,3                        ; Write
                call adv_read_write
                pop ax
+
                clc
                ret
 .bad:                                          ; No location for ADV set
@@ -470,12 +474,12 @@ adv_read_write:
 
                section .data
                align 4, db 0
+ADVSec0                db 0                    ; Undefined
+ADVSec1                db 0                    ; Undefined
 ADVDrive       db -1                   ; No ADV defined
 
                section .bss
                alignb 4
-ADVSec0                resd 1
-ADVSec1                resd 1
 ADVSecPerTrack resw 1
 ADVHeads       resw 1
 ADVOp          resb 1