Refactor parallel comms a bit

ftp.asm

@@ -1,6 +1,7 @@
 CPU 8086
 
 chunksize equ 0x20
+devicedelay equ 0x08
 
 _start:
     push bp
@@ -13,24 +14,35 @@ _start:
     mov bx, [bp-8]
     mov [bx], byte 0x42
 l0:
-    cmp word [bp-4], 0xf400
+    cmp word [bp-4], 0xf600
     jb l1
-    add sp, 8
+l2:
+    mov sp, bp
     pop bp
     ret
 l1:
+    mov ah, 0x07
+    int 0x80
+    test al, al
+    jnz l1
     push word [bp-2]
     push word [bp-4]
     mov ah, 0x05
     int 0x80
-    add sp, 4
+    test al, al
+    jz l2
+    mov ah, 0
+    add [bp-4], ax
     push word [bp-6]
     push word [bp-8]
     mov ah, 0x06
     int 0x80
-    add sp, 4
-    add word [bp-4], chunksize
-    mov cx, 0x200
-l2: dec cx
-    jnz l2
+    add sp, 8
+    mov cx, devicedelay
+l3: 
+    mov ah, 0x07
+    push cx
+    int 0x80
+    pop cx
+    loop l3             ; give the device some time to answer
     jmp l0