From ce6b5c488796671a90c5be3be974715ff308373b Mon Sep 17 00:00:00 2001
From: rswier <rswier@acm.org>
Date: Wed, 13 Apr 2016 05:09:24 -0400
Subject: [PATCH 1/5] Cleaned up B run-time

Pared down the B run-time to a minimal functionality.  This is based on
research decompiling the pdp-11 libb.a run-time.
---
 src/other/brt.s  |  4 +--
 src/other/brtb.b | 84 ++++++++++++++++++------------------------------
 2 files changed, 34 insertions(+), 54 deletions(-)

diff --git a/src/other/brt.s b/src/other/brt.s
index b86b106..0fe2046 100644
--- a/src/other/brt.s
+++ b/src/other/brt.s
@@ -112,7 +112,7 @@ jmp start
    isz sp
    jmp fetch
 
-.getchr: .+1
+.getchar: .+1
    s 2
    n 8
    n 7
@@ -125,7 +125,7 @@ jmp start
    isz sp
    jmp fetch
 
-.putchr: .+1
+.putchar: .+1
    s 2
    n 8
    n 7
diff --git a/src/other/brtb.b b/src/other/brtb.b
index 0c48c9a..34d792c 100644
--- a/src/other/brtb.b
+++ b/src/other/brtb.b
@@ -11,72 +11,52 @@ lchar(s, n, c) {
   return(c);
 }
 
-getstr(s) {
-  auto c, i;
+putnum(n, b) {
+  auto a, d;
 
-  i = 0;
-  while ((c = getchr()) != '*n') {
-    lchar(s,i,c);
-    i = i+1;
+  d = 0;
+  if (n < 0) {
+    n = -n;
+    if (n < 0) {
+      n = n-1;
+      d = 1;
+    } else
+      putchar('-');
   }
-  lchar(s,i,'*e');
-  return(s);
-}
-
-putstr(s) {
-  auto c, i;
-
-  i = 0;
-  while ((c = char(s,i)) != '*e') {
-    putchr(c);
-    i = i+1;
-  }
-}
-
-putnum(n) {
-  if (n > 9) {
-    putnum(n / 10);
-    n = n % 10;
-  }
-  putchr(n + '0');
-}
-
-octal(n) {
-  if (n > 7) {
-    octal(n / 8);
-    n = n & 7;
-  }
-  putchr(n + '0');
+  if (a = n/b)
+    putnum(a, b);
+  putchar(n%b + '0' + d);
 }
 
 printf(fmt,x1,x2,x3,x4,x5,x6,x7,x8,x9) {
-  auto adx, c, i;
+  auto adx, a, c, i, n;
   
   i = 0;
   adx = &x1;
 loop:
-  while ((c = char(fmt,i)) != '%') {
-    if (c=='*e')
+  while ((c = char(fmt, i)) != '%') {
+    if (c == '*e')
       return;
-    putchr(c);
+    putchar(c);
     i = i+1;
   }
   i = i+1;
-  c = char(fmt,i);
-  if (c=='d') {
-    if (*adx < 0) {
-      putchr('-');
-      *adx = -*adx;
-    }  
-    putnum(*adx);
-  } else if (c=='o') 
-    octal(*adx);
+  a = *adx;
+  c = char(fmt, i);
+  if (c=='d')
+    putnum(a, 10);
+  else if (c=='o') 
+    putnum(a, 8);
   else if (c=='c')
-    putchr(*adx);
-  else if (c=='s')
-    putstr(*adx);
-  else {
-    putchr('%');
+    putchar(a);
+  else if (c=='s') {
+    n = 0;
+    while ((c = char(a, n)) != '*e') {
+      putchar(c);
+      n = n+1;
+    }
+  } else {
+    putchar('%');
     goto loop;
   }
   i = i+1;

From 032dc377053f79afbe06c8126f99ea68049c74f1 Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Thu, 14 Apr 2016 10:34:54 -0400
Subject: [PATCH 2/5] sys: alloc comments

---
 src/sys/s4.s | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/sys/s4.s b/src/sys/s4.s
index fe07ba5..f31686f 100644
--- a/src/sys/s4.s
+++ b/src/sys/s4.s
@@ -18,15 +18,15 @@ alloc: 0
    lac 9f+t
    jmp alloc i		" Return from routine
 1:
-   lac s.nxfblk
-   sna
+   lac s.nxfblk		" next block with list of free blocks
+   sna			" any?
    jms halt " OUT OF DISK
-   dac s.fblks
-   jms dskrd
-   lac dskbuf
-   dac s.nxfblk
-   jms copy; dskbuf+1; s.fblks+1; 9
-   lac d10
+   dac s.fblks		" save as first free block #
+   jms dskrd		" read the block
+   lac dskbuf		" get first word (pointer to next in chain)
+   dac s.nxfblk		" save as new "next"
+   jms copy; dskbuf+1; s.fblks+1; 9	" copy remaining 9 as free
+   lac d10		" reset free count
    dac s.nfblks
    jmp alloc+1
 

From cb187e12bebb6338827b8290b5f6c8ec273ccc1c Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Fri, 15 Apr 2016 00:52:09 -0400
Subject: [PATCH 3/5] update queue (and other) storage comments

---
 src/sys/s8.s | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/src/sys/s8.s b/src/sys/s8.s
index ba3dc86..0d84bf9 100644
--- a/src/sys/s8.s
+++ b/src/sys/s8.s
@@ -95,22 +95,23 @@ dm1: -1
 
 9: .=.+t			" per-routine temp variables
 c1: .=.+1			" not used?
-q1: q2;q2+98	" ** 90?  96??	" queue element free list?
-   .=.+14
-	" queues (two words each, head and tail pointers?)
+	" character queues (two words each, head and tail pointers?)
+	"  0: free list
 	"  1: tty input
 	"  2: tty output
 	"  3: display keyboard
 	"  4: paper tape reader
 	"  5: paper tape punch
-q2:
+q1: q2;q2+98			" queue element free list
+   .=.+14			" room for 7 queues (5 used)
+q2:				" queue elements (and two words padding??)
    .+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0
    .+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0
    .+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0
    .+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0
    .+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;.+2;0;0;0
-dsploc: .=.+1
-dsplno: .=.+1
+dsploc: .=.+1			" pointer into dspbuf
+dsplno: .=.+1			" display current line number
 dspbuf:
    0065057;0147740;0160000	" display commands: see 03-scope.pdf pg 20
 	" PARAM: clear blink, clear light pen, scale=1, intensity=3
@@ -157,18 +158,19 @@ dskaddr: .=.+1			" number of block in dskbuf
 uniqpid: 1			" pid generator
 lu: .=.+4			" user (process) table entry copy
 sfiles: .=.+10			" wait addresses for special files
-		" (bit vector of waiting processes?)
+		" (bit vectors of waiting processes?)
+		" bit zero (MSB) is special, bit 1 first ulist entry, ....
 		" offsets:	0: ttyin, 1: ttyout, 2: keyboard,
 		"		3: ptr,   4: ptp,    6: display
-dpdata:
+dpdata:				" dataphone data
    dpstat: .=.+1
    dpread: .=.+1
    dpwrite: .=.+1
    dpchar: .=.+1
-dspdata:
+dspdata:			" display data
    .dspb: .=.+1
    .lpba: .=.+1	"** 4 written on listing
-crdata:
+crdata:				" card reader data
    crread: .=.+1
    crchar: .=.+1
 sysdata:			" system data 64 words saved to disk
@@ -177,7 +179,7 @@ sysdata:			" system data 64 words saved to disk
    s.fblks: .=.+10		" cached free block numbers
    s.uniq: .=.+1		" next unique value
    s.tim: .=.+2			" (up?)time in 60Hz ticks (low, high)
-	" process table
+	" user (process) table
 	" first word
 	"   bits 0:2 -- status
 	"	0: free slot
@@ -188,7 +190,7 @@ sysdata:			" system data 64 words saved to disk
 	"   bits 3:17 -- disk swap address/8
 	" second word: process pid
 	" third word:  smes/rmes status:
-	"	0: not waiting
+	"	 0: not waiting
 	"	-1: this process waiting (rmes)
 	"	other: complement of sender pid
 	" fourth word: smes message
@@ -243,7 +245,7 @@ dnode:				" directory entry:
    d.name: .=.+4		" name (space padded)
    d.uniq: .=.+1		" unique number from directory inode
       . = dnode+8
-fnode:				" open file entry
+fnode:				" open file entry (copied from u.ofiles)
    f.flags: .=.+1		" see below
    f.badd: .=.+1		" offset
    f.i: 0			" file i-number

From c8129d7fa4ab2609290ac2e6dfd892ccb9332ecb Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Fri, 15 Apr 2016 00:52:26 -0400
Subject: [PATCH 4/5] s4.s: comment disk block free and (self modifiying) char
 queue routines

---
 src/sys/s4.s | 198 +++++++++++++++++++++++++++------------------------
 1 file changed, 106 insertions(+), 92 deletions(-)

diff --git a/src/sys/s4.s b/src/sys/s4.s
index f31686f..8f273e3 100644
--- a/src/sys/s4.s
+++ b/src/sys/s4.s
@@ -3,19 +3,19 @@
 
 	" allocate a free disk block for a file (data or indirect)
 alloc: 0
-   -1			" Decrement the # free block numbers in the cache
-   tad s.nfblks		" kept at s.fblks. Jump to 1f if no free blocks left.
-   spa
-   jmp 1f
+   -1			" decrement the count
+   tad s.nfblks		" of free blocks at s.fblks
+   spa			" any left?
+   jmp 1f		"  no
    dac s.nfblks		" Update the count of free block numbers
-   tad fblksp
-   jms laci
-   dac 9f+t
-   jms copyz; dskbuf; 64
-   lac 9f+t
-   jms dskwr
-   dzm .savblk
-   lac 9f+t
+   tad fblksp		" get pointer to last valid entry in s.fblks
+   jms laci		" fetch the word
+   dac 9f+t		" save in t0
+   jms copyz; dskbuf; 64	" zero dskbuf
+   lac 9f+t		" get block number back
+   jms dskwr		" write out the zeros
+   dzm .savblk		" cancel system block write
+   lac 9f+t		" get the block number back
    jmp alloc i		" Return from routine
 1:
    lac s.nxfblk		" next block with list of free blocks
@@ -32,31 +32,32 @@ alloc: 0
 
 	" free the disk block whose number is in AC
 free: 0
-   lmq
-   lac s.nfblks
-   sad d10
-   jmp 1f
-   tad fblksp
-   dac 9f+t
-   lacq
-   dac 9f+t i
-   dzm .savblk
-   isz s.nfblks
-   jmp free i
+   lmq			" save block in MQ
+   lac s.nfblks		" get number of free blocks
+   sad d10		" 10?
+   jmp 1f		"  yes
+   tad fblksp		" no: get addr in s.fblks to store new block in
+   dac 9f+t		" save pointer
+   lacq			" get block number
+   dac 9f+t i		" save it in s.fblks
+   dzm .savblk		" cancel system block write
+   isz s.nfblks		" increment free count
+   jmp free i		" return
 1:
-   lac s.nxfblk
-   dac dskbuf
-   jms copy; s.fblks+1; dskbuf+1; 9
-   lacq
-   dac s.nxfblk
-   jms dskwr
-   dzm .savblk
-   lac d1
-   dac s.nfblks
-   jmp free i				" Return from the routine
+   lac s.nxfblk		" get head of free chain
+   dac dskbuf		" save (as chain ptr) in first word of disk buf
+   jms copy; s.fblks+1; dskbuf+1; 9	" with 9 of the 10 free blocks
+   lacq			" get the newly freed block back
+   dac s.nxfblk		" save as new head of free chain
+   jms dskwr		" write dskbuf to the newly freed block
+   dzm .savblk		" cancel system block write
+   lac d1		" reset free count to one
+   dac s.nfblks		" (the first word in s.fblks)
+   jmp free i		" Return from the routine
 t = t+1
 
 	" load AC indirect (without using indirect!)
+	" need to avoid use of indirect in interrupt service routines
 	" AC/ address
 	"   jms laci
 	" AC/ contents of address
@@ -141,92 +142,105 @@ copyz: 0
    jmp copyz i			" return
 t = t+1
 
-	" put queued character
-	" CALLED FROM PI: AVOIDS INDIRECT!!
-	" queue number in AC
-putchar: 0
-"** 01-s1.pdf page 23
-   dac 9f+t
-   cla
-   jms takeq
-      jmp putchar i
-   tad o40001
-   dac .+4
-   lac 9f+t
-   jms putq
-   lac char
-   dac q2+1 ..
-   isz putchar
-   jmp putchar i
-t = t+1
+	" Character queue management routines
+	" (CALLED FROM PI: USE OF INDIRECT AVOIDED!)
 
-	" get queued character
-	" CALLED FROM PI: AVOIDS INDIRECT!!
-	" queue number in AC:
+	" Queue numbers:
+	"  0: free list
 	"  1: tty input
 	"  2: tty output
 	"  3: display keyboard
 	"  4: paper tape reader
 	"  5: paper tape punch
-getchar: 0
+
+	" queue headers are two words: "first" and "last"(??)
+	" queue entries are two words: "next" and "char"
+
+	" put queued character
+	" character to store in "char"
+	" queue number in AC
+
+putchar: 0
+"** 01-s1.pdf page 23
+   dac 9f+t		" save queue number in t0
+   cla			" get entry from free list
    jms takeq
-      jmp i getchar
-   tad o200001
+      jmp putchar i	" none free: return w/o skip
+   tad o40001		" turn into "dac addr+1"
+   dac .+4
+   lac 9f+t		" get queue number back
+   jms putq		" add entry
+   lac char		" get char
+   dac q2+1 ..		" save in second word of queue entry
+   isz putchar		" give skip return
+   jmp putchar i
+t = t+1
+
+	" get queued character
+	" queue number in AC
+	" returns with skip if something found
+getchar: 0
+   jms takeq		" get entry from head of queue
+      jmp i getchar	"  nothing there: return w/o skip
+   tad o200001		" turn into "lac qentry+1" (fetch stored char)
    dac .+3
    cla
-   jms putq
-   lac q2+1 ..
-   isz getchar
+   jms putq		" put qentry on free list
+   lac q2+1 ..		" fetch queued character(!!!)
+   isz getchar		" give skip return
    jmp i getchar
 
-	" CALLED FROM PI: AVOIDS INDIRECT!!
+	" fetch first entry from a queue
+	" queue number in AC
+	" returns with skip if something dequeued
 takeq: 0
-   rcl
-   tad lacq1
+   rcl			" multiply queue number by two
+   tad lacq1		" add "lac q1"
    dac .+7
-   tad o640000
+   tad o640000		" turn "lac" into "dac"
    dac .+17
-   tad d1
+   tad d1		" increment addr
    dac .+14
-   tad o500000
+   tad o500000		" turn "dac" into "sad"
    dac .+5
-   lac q1 ..
-   sna
-   jmp takeq i
+   lac q1 ..		" load queue head
+   sna			" non-zero?
+   jmp takeq i		"  no: return zero w/o skip
    dac lnkaddr
-   sad q1+1 ..
-   jmp .+5
-   tad o200000
-   dac .+1
-   lac q2 ..
+   sad q1+1 ..		" different from tail(??)
+   jmp .+5		"  no -- (last entry?)
+   tad o200000		" yes: turn into lac
+   dac .+1		" save lac
+   lac q2 ..		" get next pointer from queue entry
    jmp .+3
-   cla
-   dac q1+1 ..
-   dac q1 ..
-   isz takeq
-   lac lnkaddr
+   cla			" here with head == tail(??)
+   dac q1+1 ..		" clear tail
+   dac q1 ..		" save (clear) head
+   isz takeq		" give skip return
+   lac lnkaddr		" return queue entry pointer
    jmp i takeq
 
+	" save queue entry (at lnkaddr) to a queue (queue number in AC)
 putq: 0
-   rcl
-   tad dacq1
+   rcl			" multiply by two
+   tad dacq1		" turn into "dac qhead"
    dac .+14
-   tad d1
+   tad d1		" turn into "dac qtail"
    dac .+13
-   tad o140000
+   tad o140000		" turn into "lac qtail"
    dac .+1
-   lac q1-1 ..
+   lac q1-1 ..		" fetch tail
 "** 01-s1.pdf page 24
-   sna
-   jmp .+6
-   tad o40000
+   sna			" non-zero?
+   jmp .+6		"  no: is zero
+   tad o40000		" turn into "dac qentry" (append to queue)
    dac .+2
-   lac lnkaddr
-   dac q2 ..
+   lac lnkaddr		" get new entry
+   dac q2 ..		" append to tail entry
    jmp .+3
-   lac lnkaddr
-   dac q1 ..
-   dac q1+1 ..
+   lac lnkaddr		" here with tail == 0
+   dac q1 ..		" save new entry as head
+   dac q1+1 ..		" save new tail
    jmp putq i
 
 	" NOTE!! srcdbs, collaps, dskrd, dskwr share the same "temp" vars:

From 1a4c0c3c7180ec8e3ddf0838392c90f1d70fd1bd Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Sun, 17 Apr 2016 13:25:14 -0400
Subject: [PATCH 5/5] s6.s: add comments

---
 src/sys/s6.s | 124 ++++++++++++++++++++++++++-------------------------
 1 file changed, 63 insertions(+), 61 deletions(-)

diff --git a/src/sys/s6.s b/src/sys/s6.s
index 5ba1097..891dc9b 100644
--- a/src/sys/s6.s
+++ b/src/sys/s6.s
@@ -99,6 +99,8 @@ namei: 0
    jmp 1b		"  yes: keep going
    jmp namei i		" Didn't find it, return zero in AC (without skip)
 t = t+2
+
+		" NOTE: iget/iput share "temp" vars!!!
                         " Given an i-number in AC, fetch that i-node
                         " from disk and store it in the inode buffer
 iget: 0
@@ -113,49 +115,50 @@ iget: 0
    cll; mul; 12		" Multiply the i-num within the block by 12
    lacq			" to get the offset into the block
    tad dskbufp		" Add on the base of the disk buffer
-   dac 9f+t
+   dac 9f+t		" save pointer into dskbuf in "t0"
    dac .+2
    jms copy; ..; inode; 12	" Copy 12 words from buffer to inode
    jmp iget i		" and return
 
 iput: 0
-   lac 9f+t+1
-   jms dskrd
-   law inode-1
-   dac 8
+   lac 9f+t+1		" get block number saved by iget
+   jms dskrd		" read the block
+   law inode-1		" pointer to "in core" inode
+   dac 8		" in index 8
    -1
-   tad 9f+t
-   dac 9
-   -12
-   dac 9f+t+2
+   tad 9f+t		" get saved pointer into buffer
+   dac 9		" in index 9
+   -12			" 12 word loop count
+   dac 9f+t+2		" in t2
 1:
-   lac 8 i
+   lac 8 i		" fetch source word
 
 "** 01-s1.pdf page 36
 
-   sad 9 i
-   skp
-   jmp 2f
-   isz 9f+t+2
-   jmp 1b
-   jmp iput i
-2:
-   -1
+   sad 9 i		" differs from disk?
+   skp			"  no:
+   jmp 2f		"   yes: 
+   isz 9f+t+2		" no difference: done?
+   jmp 1b		"  no: keep going
+   jmp iput i		" yes: return w/o writing to disk
+2:			" here with in-core inode changed
+   -1			" back up both pointers
    tad 8
    dac 8
    -1
    tad 9
    dac 9
 1:
-   lac 8 i
-   dac 9 i
-   isz 9f+t+2
-   jmp 1b
-   lac 9f+t+1
-   jms dskwr
-   jmp iput i
+   lac 8 i		" fetch word
+   dac 9 i		" copy to dskbuf
+   isz 9f+t+2		" done?
+   jmp 1b		"  no: keep going
+   lac 9f+t+1		" get block number
+   jms dskwr		" write back to disk
+   jmp iput i		" return
 t = t+3
 
+	" NOTE! dget/dput share "temp" vars
 	" allocate directory entry
 	" AC/ entry number
 dget: 0
@@ -164,30 +167,31 @@ dget: 0
    dac 9f+t			" save in t0
    jms pget			" get free disk block
    dac 9f+t+1			" save in t1
-   jms dskrd
-   lac 9f+t
-   and o77
-   tad dskbufp
-   dac 9f+t+2
-   dac .+2
-   jms copy; ..; dnode; 8
-   lac 9f+t
-   tad d8
-   jms betwen; d0; i.size
-      skp
-   jmp dget i
-   jms dacisize
-   dzm d.i
-   jmp dget i
+   jms dskrd			" read block
+   lac 9f+t			" get word number
+   and o77			" get word within block
+   tad dskbufp			" make pointer into dskbuf
+   dac 9f+t+2			" save in t2
+   dac .+2			" save as copy source
+   jms copy; ..; dnode; 8	" copy entry into dnode
+   lac 9f+t			" get word number
+   tad d8			" of end of new node
+   jms betwen; d0; i.size	" already allocated?
+      skp			"  no
+   jmp dget i			"   yes: return
+   jms dacisize			" store new file size
+   dzm d.i			" mark new entry as free
+   jmp dget i			" return
 
+	" write directory entry (back) to disk
 dput: 0
-   lac 9f+t+1
-   jms dskrd
-   lac 9f+t+2
-   dac .+3
-   jms copy; dnode; ..; 8
-   lac 9f+t+1
-   jms dskwr
+   lac 9f+t+1			" get disk block number back
+   jms dskrd			" read into dskbuf
+   lac 9f+t+2			" get pointer into dskbuf
+   dac .+3			" save as copy dest
+   jms copy; dnode; ..; 8	" copy into dskbuf
+   lac 9f+t+1			" get disk block number
+   jms dskwr			" write back to disk
    jmp dput i
 
 t = t+3
@@ -262,6 +266,10 @@ pget: 0
    jmp pget i				" return it
 t = t+3
 
+	" write to file referenced by loaded inode
+	" AC/ file offset
+	"    jms iwrite; addr; count
+
 iwrite: 0
    dac 9f+t				" save arg in t0
    lac iwrite				" load return address
@@ -273,14 +281,14 @@ iwrite: 0
    dac iwrite				" save as iwrite instruction
    jmp 1f
 
-	" iread from file referenced by loaded inode
+	" read from file referenced by loaded inode
 	" AC/ file offset
 	"    jms iread; addr; count
 iread: 0
    dac 9f+t				" save offset in t0
    lac cnop				" get nop
    dac iwrite				" save as iwrite instruction
-1:
+1:					" common code for iread/iwrite
    -1
    tad iread i				" get word before return addr
    dac 10				" store in index 10 & 11
@@ -289,20 +297,14 @@ iread: 0
    lac iread i				" load addr
    dac 9f+t+1				" save in t1
    isz iread				" increment return addr
-   lac o70000
+   lac o70000				" get max file size
    xct iwrite				" skip if write
    lac i.size				"  read: get file size
    cma
-   tad 9f+t				" add offset
-   cma
-   jms betwen; d0; 9f+t+1
-      lac 9f+t+1
-   dac 9f+t+2
-   cma
-   tad d1
-   sna
-   jmp iread i
-   dac 9f+t+1
+   tad 9f+t				" subtract offset
+   sna					" offset == size?
+   jmp iread i				"  yes, return
+   dac 9f+t+1				" save size-offset in t1
 1:
    lac 9f+t
    jms pget
@@ -312,7 +314,7 @@ iread: 0
    and o77
    tad dskbufp
    tad dm1
-   xct iwrite
+   xct iwrite				" skip if write
    jmp .+3
    dac 10
 cskp: