memdisk: additional comments in memdisk.inc and postprocess.pl

Just a sprinkling of comments adding further description to the code.

diff --git a/memdisk/memdisk.inc b/memdisk/memdisk.inc
index 1e2076b..0df6c77 100644 (file)
--- a/memdisk/memdisk.inc
+++ b/memdisk/memdisk.inc
@@ -36,6 +36,7 @@
 
 %endif ; DEBUG_TRACERS
 
+; Flags we test our configuration against
 %define CONFIG_READONLY        0x01
 %define CONFIG_RAW     0x02
 %define CONFIG_SAFEINT 0x04
@@ -104,6 +105,8 @@ Int13Start:
                xor dl,[cs:DriveNo]
                pop dx
                js .nomatch             ; If SF=0, we have a class match here
+                                       ; 0x00 the sign bit for FD
+                                       ; 0x80 the sign bit for HD
                jz .our_drive           ; If ZF=1, we have an exact match
                cmp dl,[cs:DriveNo]
                jb .nomatch             ; Drive < Our drive
@@ -115,13 +118,13 @@ Int13Start:
                pushf
                push bp
                mov bp,sp
-               cmp byte [cs:SavedAX+1],08h
+               cmp byte [cs:SavedAX+1],08h     ; Get drive params function?
                je .norestoredl
-               cmp byte [cs:SavedAX+1],15h
+               cmp byte [cs:SavedAX+1],15h     ; Get disk type function?
                jne .restoredl
                test byte [bp+4],80h    ; Hard disk?
                jnz .norestoredl
-.restoredl:
+.restoredl:                            ; DL should have number of drives
                mov dl,[bp+4]
 .norestoredl:
                push ax
@@ -129,7 +132,7 @@ Int13Start:
                push ds
                mov ax,[bp+2]           ; Flags
                lds ebx,[cs:Stack]
-               mov [bx+4],al           ; Arithmetric flags
+               mov [bx+4],al           ; Arithmetic flags
                pop ds
                pop ebx
                pop ax
@@ -166,7 +169,7 @@ DoneWeird:
                and ah,ah
 
                lds ebx,[Stack]
-               ; This sets the low byte (the arithmetric flags) of the
+               ; This sets the low byte (the arithmetic flags) of the
                ; FLAGS on stack to either 00h (no flags) or 01h (CF)
                ; depending on if AH was zero or not.
                setnz [bx+4]            ; Set CF iff error
@@ -181,7 +184,8 @@ Reset:
                TRACER 'R'
                xor ax,ax               ; Bottom of memory
                mov es,ax
-               test dl,dl              ; Always pass it on if we are resetting HD
+               test dl,dl              ; Always pass it on if we are
+                                       ; resetting HD
                js .hard_disk           ; Bit 7 set
                ; Some BIOSes get very unhappy if we pass a reset floppy
                ; command to them and don't actually have any floppies.
@@ -194,7 +198,8 @@ Reset:
                jmp .pass_on            ; ... otherwise pass it to the BIOS
 .hard_disk:
                ; ... same thing for hard disks, sigh ...
-               cmp byte [es:0x475],1   ; BIOS variable for number of hard disks
+               cmp byte [es:0x475],1   ; BIOS variable for number of hard
+                                       ; disks
                jbe success
 
 .pass_on:
@@ -354,7 +359,7 @@ EDDWrite:
                TRACER 'w'
 
                call edd_setup_regs
-               xchg esi,edi
+               xchg esi,edi            ; Opposite direction of a Read!
                call bcopy
                xor ax,ax
                ret
@@ -397,7 +402,8 @@ EDDGetParms:
                ret
 %endif ; EDD
 
-               ; Set up registers as for a "Read", and compares against disk size.
+               ; Set up registers as for a "Read", and compares against disk
+               ; size.
                ; WARNING: This fails immediately, even if we can transfer some
                ; sectors.  This isn't really the correct behaviour.
 setup_regs:
@@ -589,21 +595,22 @@ Int15Start:
 oldint15:      pop bp
                jmp far [cs:OldInt15]
 
-int15_e801:
+int15_e801:                            ; Get mem size for > 64 MB config
                mov ax,[cs:Mem1MB]
                mov cx,ax
                mov bx,[cs:Mem16MB]
                mov dx,bx
                jmp short int15_success
 
-int15_e881:
+int15_e881:                            ; Get mem size for > 64 MB config
+                                       ; 32-bit code
                mov eax,[cs:Mem1MB]
                mov ecx,eax
                mov ebx,[cs:Mem16MB]
                mov edx,ebx
                jmp short int15_success
 
-int15_88:
+int15_88:                              ; Get extended mem size
                mov ax,[cs:MemInt1588]
                jmp short int15_success
 
@@ -805,7 +812,8 @@ Int13Funcs  dw Reset                ; 00h - RESET
                dw Invalid              ; 06h - FORMAT TRACK AND SET BAD FLAGS
                dw Invalid              ; 07h - FORMAT DRIVE AT TRACK
                dw GetParms             ; 08h - GET PARAMETERS
-               dw InitWithParms        ; 09h - INITIALIZE CONTROLLER WITH DRIVE PARAMETERS
+               dw InitWithParms        ; 09h - INITIALIZE CONTROLLER WITH
+                                       ;       DRIVE PARAMETERS
                dw Invalid              ; 0Ah
                dw Invalid              ; 0Bh
                dw Seek                 ; 0Ch - SEEK TO CYLINDER

diff --git a/memdisk/postprocess.pl b/memdisk/postprocess.pl
index f8cba96..fcda478 100755 (executable)
--- a/memdisk/postprocess.pl
+++ b/memdisk/postprocess.pl
@@ -12,8 +12,10 @@
 ## -----------------------------------------------------------------------
 
 #
-# Postprocess the memdisk binary.
-#
+# Postprocess the memdisk binary.  Used during the 'make' process.
+# We write memdisk16.bin out to the final memdisk kernel, pad it to an
+# integral 512-byte sector length, write this number of sectors into the
+# kernel header field "setup_sects", then append memdisk32.bin
 
 eval { use bytes; };