Merge pull request #19 from philbudne/master

fix as7 relative subtraction; system & as comments

src/cmd/as.s

@@ -193,8 +193,8 @@ process: 0
    lac dot+1			" get "." value
    dac lvrand
    lac dot			" get "." type??
-   sad d3			" three?
-   jmp proc4			"  no, give "." error
+   sad d3			" three (user defined symbol?)?
+   jmp proc4			"  yes, give "." error
    sza				" zero?
    jmp proc1			"  no
    -1				" yes (".." type)

src/sys/s2.s

@@ -110,7 +110,7 @@
       skp
    jms error
    lac d1
-   dac mode
+   dac mode			" save mode bits for access
    jms access
    jms dslot
    lac u.base
@@ -131,8 +131,8 @@
 .unlink:
    jms argname
    dac u.base
-   lac d1
-   dac mode
+   lac d1			" mode bit 1 (write?)
+   dac mode			" save for access call
    jms access
    dac d.i
    jms dput
@@ -162,8 +162,8 @@
    lac u.cdir
    jms namei; 0:0
       jms error
-   lac d1
-   dac mode
+   lac d1				" mode bit 1 (write?)
+   dac mode				" save for access call
    jms access
    jms copy; 1:0; d.name; 4
    jmp okexit
@@ -197,8 +197,8 @@
    sza
    lac d1
    sna
-   lac d2
-   dac mode
+   lac d2			" mode bit 2 (read?)
+   dac mode			" save for access call
    lac u.cdir
    jms namei; 0:0
       jms error
@@ -218,8 +218,8 @@
    jmp open1
 
 .creat:
-   lac d1
-   dac mode
+   lac d1				" mode bit 1 (write?)
+   dac mode				" save for access call
    jms arg
    dac .+2
    jms copy; ..; name; 4

src/sys/s4.s

@@ -280,6 +280,9 @@ dskwr: 0
    jmp dskwr i
 t = t+3
 
+	" called with:
+	" AC/ block
+	"   jms dskio; dsld_bits
 dskio: 0
    dac dskaddr
    cll; idiv; 80
@@ -304,6 +307,8 @@ dskio: 0
    jmp dskio i
 t = t+1
 
+	" called with:
+	"   jms dsktrans; -WC; MAC; addr_ptr?; dsld_ptr
 dsktrans: 0
    -10
    dac 9f+t
@@ -312,25 +317,25 @@ dsktrans: 0
    tad dsktrans
    dac 12
 "** 01-s1.pdf page 26
-   dscs
+   dscs				" clear status register
    lac 12 i
-   dslw
+   dslw				" load WC
    lac 12 i
-   dslm
+   dslm				" load MAC
    lac 12 i
    jms laci
-   dsld
+   dsld				" load TA & SA
    dzm .dskb
    lac 12 i
    jms laci
    jms laci
-   dsls
-   lac .dskb
+   dsls				" load status
+   lac .dskb			" check for interrupt
    sna
    jmp .-2
-   lac .dske
+   lac .dske			" get status from interrupt
    sma
-   jmp 12 i
+   jmp 12 i			" return
    isz 9f+t
    jmp 1b
    jms halt " 10 disk errors

src/sys/s5.s

@@ -22,7 +22,7 @@ access: 0
    sad i.uid
    lrs 2
    lacq
-   and mode
+   and mode				" mode from system call
    sza
    jmp access i
    jms error
@@ -138,6 +138,8 @@ dslot: 0
    jmp 1b
    jmp dslot i
 
+	" called with:
+	" AC/ mode
 icreat: 0
    dac 9f+t
    jms dslot

tools/as7

@@ -465,15 +465,29 @@ sub parse_expression {
 
 	if ($op eq '+') {
 	    $word += $syllable;
+	    $flags |= $sylflags;
 	}
 	elsif ($op eq '-') {
 	    $word -= $syllable;
+	    if ($flags & $RELATIVE) {
+		# relative-relative => absolute!
+		if ($sylflags & $RELATIVE) {
+		    $flags &= ~$RELATIVE;
+		}
+		# else: relative-abs => relative (no change)
+	    }
+	    else {		# word is absolute
+		if ($sylflags & $RELATIVE) {
+		    err('A', 'absolute value minus relative??');
+		}
+		# else: absolute-absolute => absolute (no change)
+	    }
 	}
 	else {
 	    $word |= $syllable;
+	    $flags |= $sylflags;
 	}
 	$word &= 0777777;
-	$flags |= $sylflags;
 	printf("\tsyllable: %#o word: %#o\n", $syllable, $word) if ($debug);
     }
 }