mbr_ho.bin: Fix bug in $PnP Scan; PressAnyKey; compare [ES:DI]

Also numerous uses of *w opcodes and spacing fixes

diff --git a/mbr/mbr_ho.S b/mbr/mbr_ho.S
index 993b0c3..48220c2 100644 (file)
--- a/mbr/mbr_ho.S
+++ b/mbr/mbr_ho.S
@@ -33,21 +33,24 @@
  * mbr_ho.S: MBR-like codeblock to display handoff data
  *
  * Displays the values of DL, DS, SI, the contents of [DS:SI] (16 bytes),
- * the values of ES, DI then the contents of [ES:DI] (4 bytes) then reports
- * a boot failure.
+ * the values of ES, DI, the contents of [ES:DI] (4 bytes), scans memory for
+ * $PnP then reports a boot failure.
+ *
+ * This should (hopefully) be only 8086 code
  */
 
-#define DEBUG_MARKER1
-#define DEBUG_START
-#define DEBUG_LOADE
-#define DEBUG_PNP
+// #define DEBUG_MARKER1       /* Insert markers in binary */
+// #define DEBUG_START /* Print entry addresses at start */
+// #define DEBUG_LOADE /* movw versus pop */
+#define DEBUG_PNP      /* Scan for $PnP and show address */
+#define DEBUG_PAK      /* Press Any Key before boot fail */
 
 #ifdef DEBUG_MARKER1
        .macro ASCII_MARKER1 s:vararg
-       .ascii \s
+       .ascii  \s
        .endm
 #else  /* DEBUG_MARKER1 */
-       .macro ASCII_MARKER1 s
+       .macro ASCII_MARKER1 s:vararg
        .endm
 #endif /* DEBUG_MARKER1 */
 
@@ -65,13 +68,20 @@
        .text
 
 entry          = 0x7c00
-pnps           = (entry)
-pnpi           = (pnps-2)
-stack          = (pnpi-2)
-e_di           = (stack-2)
-e_es           = (stack-4)
-e_si           = (stack-6)
-e_ds           = (stack-8)
+stack          = (entry)
+e0_ax          = (stack-2)
+e0_cx          = (stack-4)
+e0_dx          = (stack-6)
+e0_bx          = (stack-8)
+e0_sp          = (stack-10)
+e0_bp          = (stack-12)
+e0_si          = (stack-14)
+e0_di          = (stack-16)
+e0_bot         = (stack-16)
+e_di           = (e0_bot-2)    /* Original register values from entry point */
+e_es           = (e0_bot-4)
+e_si           = (e0_bot-6)
+e_ds           = (e0_bot-8)
 
 BIOS_page      = 0x462
 
@@ -81,14 +91,15 @@ _start:
        xorw    %ax, %ax
        movw    %ax, %ss
        movw    $stack, %sp
-       sti
-       cld
+       pushaw
        pushw   %di             /* es:di -> $PnP header */
        pushw   %es
        pushw   %si
        pushw   %ds
-       push    %cs
-       pop     %ds
+       sti
+       cld
+       pushw   %cs
+       popw    %ds
 
 #ifdef DEBUG_START
        pushw   %dx
@@ -96,11 +107,10 @@ _start:
        movw    $(_start),%dx   /* 0x0600 mbr.ld .text address */
        call    wrhexw
        call    crlf
-//     movw    $(entry - _start),%dx   /* 0x7C00 */
        call    caddr
-caddr: popw    %ax
-       sub     $(caddr - _start), %ax
-       movw    %ax, %dx        /* Same size as pushw %ax;popw %dx */
+caddr:
+       popw    %dx
+       subw    $(caddr - _start), %dx
        call    wrhexw
        call    crlf
        popw    %dx
@@ -113,7 +123,6 @@ pr_dl:      call    wrstr
        /* DS */
 pr_ds: call    wrstr
        .ascii  "  DS: \0"
-//     popw    %dx
        LOADE   ds, dx
        pushw   %dx
        popw    %es
@@ -121,7 +130,6 @@ pr_ds:      call    wrstr
        /* SI */
 pr_si: call    wrstr
        .ascii  "  SI: \0"
-//     popw    %dx
        LOADE   si, dx
        pushw   %dx
        popw    %di
@@ -135,14 +143,12 @@ pr_si:    call    wrstr
        /* ES */
 pr_es: call    wrstr
        .ascii  "ES: \0"
-//     popw    %dx
        LOADE   es, dx
        pushw   %dx
        popw    %es
        call    wrhexw
 pr_di: call    wrstr
        .ascii  "  DI: \0"
-//     popw    %dx
        LOADE   di, dx
        pushw   %dx
        popw    %di
@@ -151,8 +157,19 @@ pr_di:     call    wrstr
        /* ES:DI */     /* %es:0(%di) */
        movw    $4, %cx
        call    wrhexbses
-       call    crlf
 
+#ifdef DEBUG_PNP
+       subw    $4, %si
+       es lodsw
+       cmpw    $0x5024, %ax
+       jne     scn_pnp
+       es lodsw
+       cmpw    $0x506E, %ax
+       jne     scn_pnp
+       call    wrstr
+       .ascii  " =$PnP\0"
+scn_pnp:
+       call    crlf
        /* $PnP Scan */
        movw    $0xf000, %dx
        pushw   %dx
@@ -163,10 +180,10 @@ pr_di:    call    wrstr
        movw    $0x5024, %dx
        movw    $0x506E, %bx
 ch_pnp:        es lodsw
-       cmp     %dx, %ax
+       cmpw    %dx, %ax
        jne     ch_pnp_l
        es lodsw
-       cmp     %bx, %ax
+       cmpw    %bx, %ax
        je      pr_pnp
 ch_pnp_l:
        addw    $14, %si
@@ -174,15 +191,18 @@ ch_pnp_l:
        loopw   ch_pnp
        jmp     end
 pr_pnp:
+       pushw   %si
        call    wrstr
        .ascii  "$PnP-\0"
        movw    %es, %dx
        call    wrhexw
        movb    $':, %al
        call    wrchr
-       movw    %si, %dx
+       popw    %dx
        andw    $0xFFF0, %dx
        call    wrhexw
+#endif /* DEBUG_PNP */
+
        call    crlf
 
 end:
@@ -210,8 +230,8 @@ wrstr_d:
        ret
 
 crlf:
-       call wrstr
-       .ascii "\r\n\0"
+       call    wrstr
+       .ascii  "\r\n\0"
        ret
 
        ASCII_MARKER1   "hx"
@@ -259,6 +279,12 @@ wrhexbses_l:
 data:
        ASCII_MARKER1   "bf"
 bootfail:
+#ifdef DEBUG_PAK
+       call wrstr
+       .ascii  "\r\n\r\nPress any key\r\n\0"
+       xor     %ax, %ax
+       int     $0x16
+#endif
        int     $0x18           /* Boot failure */
 die:
        hlt