From bb72a137a55c6b9ccc4a0eb74379c9ad6fad8892 Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Mon, 29 Feb 2016 13:38:51 -0500
Subject: [PATCH 1/6] update, extend asm_syntax.txt

---
 misc/asm_syntax.txt | 277 ++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 254 insertions(+), 23 deletions(-)

diff --git a/misc/asm_syntax.txt b/misc/asm_syntax.txt
index 6e9b072..596f8bc 100644
--- a/misc/asm_syntax.txt
+++ b/misc/asm_syntax.txt
@@ -1,42 +1,273 @@
-Basics of the Unix assembler syntax
+Basics of the "Unix v0" 'as' assembler syntax and PDP-7 coding:
 
-Lines starting with " are comment lines
+ASSEMBLER SYNTAX:
+=================
+
+Anything from " to end of line is a comment.
 
 . is the location counter, where the next code or constant will be placed
-.. is the relocation counter
+.. is the relocation counter (not currently handled)
 
-t = 0		Sets a built-in variable to this value without generating any machine code.
-		Variables so far are . .. and t. Not sure what t's purpose is yet.
+Symbol names start with a letter, and can contain letters and "."
+The dump of label values in "scans/sysmap" appears to show truncation
+after 8 characters (not currently enforced by the "as7" Perl script).
 
-orig:		is a label. It looks like labels can have dots in them.
-		Dots seem to separate structures and fields, e.g. u.base
-		but there are some symbols that start with dots, e.g. .seek
+symbol = expression
 
-jms copy; 10; u.rg+2; 6		Semicolons separate instructions and
-				word expressions that follow the instruction
+	Sets a built-in variable to this value without generating any
+	machine code.
 
-				Some expressions are 0:0, not sure about this.
-				Is it two 9-bit fields? No idea
+	as7 enters machine instructions and the indirect bit (i)
+	into the variable table.
 
-jmp 1f		Jump back to the closest 1:	label
-jmp 1b		Jump forward to the closest 1:	label
+label:	is a label.
 
-Some lines are indented differently to others e.g.
+	single digit decimal numbers can be used as "local" labels,
+	which are referenced with Nf and Nb:
 
-	jms betwen; o10000; o17762
-	   jms error
-	dac .+1
+	jmp 1f		Jump back to the closest 1: label
+	jmp 1b		Jump forward to the closest 1: label
 
-I think this is to indicate the skip logic, but it plays no part in the assembly syntax.
-
--1 occurs instead of instructions, so it looks like the assembler allows
-literal constants at any time.
+multiple words can be entered on one line, separated by semi-colon.
 
 String literals seem to be two characters decorated with < > characters, e.g.
 "ab" is <a>b. I'm guessing these are placed as pairs in one word. The syntax
 is confusing, because I've also seen <no> ; 040 ; <fi> ; <le>; <s 012 which
 appears to mean "no files\n".
 
-Looks like a line can contain multiple labels, e.g. o12: d10: 10
+A line can contain multiple labels, e.g. o12: d10: 10
 
 Numeric literals: 0xx are octal values, [1-9]xx are decimal values.
+
+CONVENTIONS:
+============
+
+Because there is no immediate mode (and "as" lacks the literal syntax
+found in DEC assemblers), there is a convention for literal (manifest)
+constants:
+
+	dNNN indicates the location of a constant for decimal NNN.
+	oOOO for octal constant OOO.
+	dmN (decimal minus) indicates a constant for decimal -N.
+
+High order bits of the "law" (load ac with word) instruction are all
+ones, so "-1" as an instruction loads -1 into AC.
+
+Subroutine arguments are often located in the words following the
+call. When an argument is a variable, sometimes a "0:" local label is
+used to tag the location:
+
+	jms namei; 0:0
+
+Indentation is (sometimes) used to indicate an instruction
+or subroutine that may skip:
+
+	jms betwen; o10000; o17762
+	   jms error
+	dac .+1
+
+NOTE! the "betwen" (between) routine (which appears in multiple
+places) takes ADDRESSES of values (which can be literals, as above),
+or could be symbol names for variables.
+
+I haven't seen any cases where "skip chains" (sequences of skip
+instructions) are indicated by multiple indents.
+
+There is no hardware stack, so the only form of subroutine call (jms)
+is "impure" and leaves the (updated) program counter in the first word
+of the subroutine, and execution starts on the second word.
+
+Routines which fetch arguments from after the jms instruction may do:
+
+	 routine: 0
+	    lac routine i	" pick up argument after jms
+	    dac temp		" store in temp location
+	    isz routine		" increment return PC to skip argument
+
+Routines which (optionally) skip (eg; on success) may use "isz
+routine" to (conditionally) increment the return PC.
+In the system code t is used as a (current) offset into a block of
+temporary location(s) for a routine or group of routines , at label
+9f, so you'll see:
+
+    this:
+	0
+	lac 9f+t+N
+    ....
+    t=t+M
+    ....
+    that:
+	0
+	lac 9f+t+I
+    ....
+    t=t+J
+    .....
+    .....
+    .....
+    9f:
+       .=.+t
+
+
+HARDWARE:
+=========
+
+References:
+http://simh.trailing-edge.com/docs/architecture18b.pdf
+http://www.soemtron.org/pdp7.html
+http://www.soemtron.org/pdp7history.html
+
+NOTE!  All opcodes are defined in "sop.s" (and in "as7") and are
+commented as below.
+
+The PDP-4/7/9/15 family started as a simplified version of the PDP-1,
+(itself an evolution of the TX-0, designed at MIT Lincoln Labs). The
+PDP-4 wasn't very successful (offering 5/8 PDP-1 performance at 1/2
+the price).
+
+The PDP-7 was originally concieved of as a repackaging of the PDP-1,
+but DEC had a built up more system software for the PDP-4 than for the
+PDP-1 (including a FORTRAN II compiler!), so they continued with the
+new architecture.   See Bob's paper (first link above) for more detail.
+
+The Living Computing Museum in Seattle has a running PDP-7, and
+intends to build simulated disk hardware to enable running "Unix v0".
+
+Words are 18 bits, words are typically represented as six octal digits.
+
+There is one 18 bit accumulator, called "AC".
+
+The "LINK" register is a 1-bit register that is included in shifts.
+
+The Extended Arithmetic Element (EAE) option adds an "MQ" register which
+has limited uses.
+
+Bit numbering is "big endian": bit zero is 400000.
+
+There are no "addressing" modes: memory referencing instructions,
+(opcodes 0 thru 060) decode the low 14 bits as:
+    I (020000) "indirect" bit
+    Y (017777) 13-bit address field.
+
+When the "I" bit is clear, the "Y" field is the address of the operand.
+When the "I" bit is set, the word referenced by the contents of the
+word addressed by "Y" field is used as the operand.
+
+Unlike the PDP-1 (and PDP-6/10) indirect references are not
+multi-level, and end after the first indirect fetch.
+
+The PDP-7 found by Ken Thompson apparently did not have extended
+memory or memory protection options and could directly reference all
+8K words of memory (at all times).
+
+Unix system code appears to have resided in the low 4K of memory, and
+a single user program in the high 4K.  The system had a "fast"
+fixed-head disk, but indirect memory access locks out DMA by the disk
+controller, and indirect access cannot be used while disk transfers
+are active (the interrupt service routines for clock and TTY, are
+coded without using indirect!).  Because of this, disk access cannot
+be "overlapped" with user code, but users are free to use "indirect"
+freely.
+
+When locations 010 through 017 of memory are referenced *INDIRECTLY*,
+they auto-increment after access, and can be used as "index
+registers".
+
+System calls are made using the "CAL" (call) instruction (octal 00).
+The Y field indicates the system call number.  "CAL" behaves like "jms
+020".  "CAL" with the "I" bit set behaves like "jms 20 i".  The system
+handler appears to deal with both (although the non-indirect form
+destroys the contents of location 020), and has a longer code path, so
+it seems likely that "sys=cal i" became the preferred system call at
+some point?
+
+The kernel preserves the contents of the users' AC and MQ registers
+and locations 8-15 in the "userdata" block (symbols u.ac, u.mq and
+u.rq).  Location u.rq+8 is the saved PC of the last system call.
+
+The "save" system call (and any undefined system call) write high 4K
+of memory and the "userdata" block (to fd 1?????)
+
+The system did not have advanced interrupt processing hardware, so all
+"priority interrupts" (also known in the past as "address break"
+processing) dispatched as if a "jms 0" was executed, and are processed
+in the "pibreak" routine.
+
+Summary of memory instructions (from annotated sop.s):
+
+    dac = 0040000		" MEM: deposit AC
+    jms = 0100000		" MEM: jump to subroutine
+    dzm = 0140000		" MEM: deposit zero to memory
+    lac = 0200000		" MEM: load AC
+    xor = 0240000		" MEM: XOR with AC
+    add = 0300000		" MEM: one's complement add
+    tad = 0340000		" MEM: two's complement add
+    xct = 0400000		" MEM: execute
+    isz = 0440000		" MEM: increment and skip if zero
+    and = 0500000		" MEM: AND with memory
+    sad = 0540000		" MEM: skip if AC different
+    jmp = 0600000		" MEM: jump
+
+Other instruction groups do not interpret the "I" bit, and all begin
+with '7' in the high three bits.
+
+I/O Transfer (or IOT) have 111000 (070) in the high six bits. the next
+six bits (two octal digits) indicate the device number.
+
+Operate (OPR) which is "microcoded" with low order bits indicating
+"micro operations" to be performed have 11110 (074) in the high four
+bits:
+
+    cma = 0740001		" OPR: complement AC
+    ral = 0740010		" OPR: rotate AC left
+    rar = 0740020		" OPR: rotate AC right
+    hlt = 0740040		" OPR: halt
+    sma = 0740100		" OPR: skip on minus AC
+    sza = 0740200		" OPR: skip on zero AC
+    snl = 0740400		" OPR: skip on non-zero link
+    skp = 0741000		" OPR: skip unconditionally
+    sna = 0741200		" OPR: skip on negative AC
+    szl = 0741400		" OPR: skip on zero link
+    rtl = 0742010		" OPR: rotate two left
+    rtr = 0742020		" OPR: rotate two right
+    cll = 0744000		" OPR: clear link
+    rcl = 0744010		" OPR: clear link, rotate left
+    rcr = 0744020		" OPR: clear link, rotate right
+    cla = 0750000		" OPR: clear AC
+    las = 0750004		" OPR: load AC from switches
+
+With some limitations, OPR instructions can be OR-ed together.
+(Ordering of operations is determined by the hardware, not by their
+order in the source!!):
+
+  sna cla		" skip on negative AC, clear AC
+  sna spa		" skip on negative or positive AC
+  sna ral		" skip on negative AC, rotate AC left
+  cla cll sza		" skip on AC zero, clear AC, clear LINK
+
+The last "operate" instruction is not microcoded:
+    law = 0760000		" OPR: load accumulator with (instr)
+
+and as noted above, is often coded directly as an immediate negative constant.
+
+Unix v0 depends on the EAE option, which uses instructions with 064 in
+the top four bits, and is used for multiply, divide, and the 18-bit MQ
+register:
+
+    lrs = 0640500		" EAE: long right shift
+    lrss = 0660500		" EAE: long right shift, signed
+
+    lls = 0640600		" EAE: long left shift
+    llss = 0660600		" EAE: long left shift, signed
+
+    als = 0640700		" EAE: AC left shift
+    alss = 0660700		" EAE: AC left shift, signed
+
+    mul = 0653323		" EAE: multiply
+    idiv = 0653323		" EAE: integer divide
+
+    lacq = 0641002		" EAE: load AC with MQ
+    clq = 0650000		" EAE: clear MQ
+    omq = 0650002		" EAE: OR MQ into AC
+    cmq = 0650004		" EAE: complement MQ
+    lmq = 0652000		" EAE: load MQ from AC
+

From b3259cc9d19cec735753226e199da90424671fe7 Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Mon, 29 Feb 2016 13:40:20 -0500
Subject: [PATCH 2/6] add (tab separated) comments

---
 src/sys/sop.s | 180 +++++++++++++++++++++++++-------------------------
 1 file changed, 89 insertions(+), 91 deletions(-)

diff --git a/src/sys/sop.s b/src/sys/sop.s
index 22ca2a4..124ee9d 100644
--- a/src/sys/sop.s
+++ b/src/sys/sop.s
@@ -1,97 +1,95 @@
 "** 01-s1.pdf page 62
 " sop
 
-dac = 0040000
-jms = 0100000
-dzm = 0140000
-lac = 0200000
-xor = 0240000
-add = 0300000
-tad = 0340000
-xct = 0400000
-isz = 0440000
-and = 0500000
-sad = 0540000
-jmp = 0600000
-nop = 0740000
-i = 020000
-law = 0760000
-cma = 0740001
-las = 0750004
-ral = 0740010
-rar = 0740020
-hlt = 0740040
-sma = 0740100
-sza = 0740200
-snl = 0740400
-skp = 0741000
-sna = 0741200
-szl = 0741400
-rtl = 0742010
-rtr = 0742020
-cil = 0744000
-rcl = 0744010
-rcr = 0744020
-cia = 0750000
-lrs = 0640500
-lrss = 0660500
-lls = 0640600
-llss = 0660600
-als = 0640700
-alss = 0660700
-mul = 0653323
-idiv = 0653323
-lacq = 0641002
-clq = 0650000
-omq = 0650002
-cmq = 0650004
-lmq = 0652000
+dac = 0040000			" MEM: deposit AC
+jms = 0100000			" MEM: jump to subroutine
+dzm = 0140000			" MEM: deposit zero to memory
+lac = 0200000			" MEM: load AC
+xor = 0240000			" MEM: XOR with AC
+add = 0300000			" MEM: one's complement add
+tad = 0340000			" MEM: two's complement add
+xct = 0400000			" MEM: execute
+isz = 0440000			" MEM: increment and skip if zero
+and = 0500000			" MEM: AND
+sad = 0540000			" MEM: skip if AC different
+jmp = 0600000			" MEM: jump
+nop = 0740000			" OPR: no-op
+i = 020000			" indirect
+law = 0760000			" OPR: load accumulator with (instr)
+cma = 0740001			" OPR: complement AC
+las = 0750004			" OPR: load AC from switches
+ral = 0740010			" OPR: rotate AC left
+rar = 0740020			" OPR: rotate AC right
+hlt = 0740040			" OPR: halt
+sma = 0740100			" OPR: skip on minus AC
+sza = 0740200			" OPR: skip on zero AC
+snl = 0740400			" OPR: skip on non-zero link
+skp = 0741000			" OPR: skip unconditionally
+sna = 0741200			" OPR: skip on negative AC
+szl = 0741400			" OPR: skip on zero link
+rtl = 0742010			" OPR: rotate two left
+rtr = 0742020			" OPR: rotate two right
+cll = 0744000			" OPR: clear link
+rcl = 0744010			" OPR: clear link, rotate left
+rcr = 0744020			" OPR: clear link, rotate right
+cla = 0750000			" OPR: clear AC
+lrs = 0640500			" EAE: long right shift
+lrss = 0660500			" EAE: long right shift, signed
+lls = 0640600			" EAE: long left shift
+llss = 0660600			" EAE: long left shift, signed
+als = 0640700			" EAE: AC left shift
+alss = 0660700			" EAE: AC left shift, signed
+mul = 0653323			" EAE: multiply
+idiv = 0653323			" EAE: integer divide
+lacq = 0641002			" EAE: load AC with MQ
+clq = 0650000			" EAE: clear MQ
+omq = 0650002			" EAE: OR MQ into AC
+cmq = 0650004			" EAE: complement MQ
+lmq = 0652000			" EAE: load MQ from AC
 
-dscs = 0707141
-dslw = 0707124
-dslm = 0707142
-dsld = 0707104
-dsls = 0707144
-dssf = 0707121
-dsrs = 0707132
-
-iof = 0700002
-ion = 0700042
-caf = 0703302
-clon = 0700044
-clsf = 0700001
+dscs = 0707141			" DSK: clear status register
+dslw = 0707124			" DSK: clear and load WC from AC
+dslm = 0707142			" DSK: clear and load MAC from AC
+dsld = 0707104			" DSK: clear and load TA and SA from AC
+dsls = 0707144			" DSK: load status
+dssf = 0707121			" DSK: skip on flags
+dsrs = 0707132			" DSK: read status register
 
+iof = 0700002			" PIC: interrupts off
+ion = 0700042			" PIC: interrupts on
+caf = 0703302			" CPU: clear all flags
+clon = 0700044			" CLK: clear flag, enable
+clsf = 0700001			" CLK: skip if overflow
 "** 01-s1.pdf page 63
-clof = 0700004
-ksf = 0700301
-krb = 0700312
-tsf = 0700401
-tcf = 0700402
-tls = 0700406
-sck = 0704301
-cck = 0704304
-lck = 0704312
-rsf = 0700101
-rsa = 0700104
-rrb = 0700112
-psf = 0700201
-pcf = 0700202
-psa = 0700204
-cdf = 0700501
-lds = 0701052
-lda = 0701012
-wcga = 0704206
-raef = 0700742
-rlpd = 0700723
-beg = 0700547
-spb = 0704401
-cpb = 0704404
-lpb = 0704412
-wbl = 0704424
-dprs = 0704752
-dpsf = 0704741
-dpcf = 0704761
-dprc = 0704712
-crsf = 0706701
-crrb = 0706712
-
+clof = 0700004			" CLK: clear flag, disable
+ksf = 0700301			" KBD: skip if flag set
+krb = 0700312			" KBD: read buffer
+tsf = 0700401			" TTY: skip if flag set
+tcf = 0700402			" TTY: clear flag
+tls = 0700406			" TTY: load buffer, select
+sck = 0704301			" S-2: skip on console keyboard
+cck = 0704304			" S-2: clear console keyboard
+lck = 0704312			" S-2: load console keyboard
+rsf = 0700101			" PTR: skip if flag set
+rsa = 0700104			" PTR: select alphanumeric mode
+rrb = 0700112			" PTR: clear flag, or read buffer
+psf = 0700201			" PTP: skip if flag set
+pcf = 0700202			" PTP: clear flag
+psa = 0700204			" PTP: alphanumeric mode
+cdf = 0700501			" ???
+lds = 0701052			" S-2: load display status
+lda = 0701012			" S-2: load display address
+wcga = 0704206			" S-2: ???
+raef = 0700742			" S-2: resume after edges flag
+rlpd = 0700723			" S-2: resume after light pen stop, disabled
+beg = 0700547			" S-2: begin
+spb = 0704401			" S-2: skip on push button flag
+cpb = 0704404			" S-2: clear push button flag
+lpb = 0704412			" S-2: load push buttons
+wbl = 0704424			" S-2: write button lights
+dprs = 0704752			" dataphone: read status
+dpsf = 0704741			" dataphone: skip on flag
+dpcf = 0704761			" dataphone: clear flag
+dprc = 0704712			" dataphone: read character
+crsf = 0706701			" CDR: skip if ready
+crrb = 0706712			" CDR: read buffer

From 2def710c4845a8ab3f36e257cb762e6ffc5008c6 Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Mon, 29 Feb 2016 14:22:27 -0500
Subject: [PATCH 3/6] add some (tab separated) comments; fixed some typos

---
 src/sys/s1.s | 86 ++++++++++++++++++++++++++--------------------------
 src/sys/s2.s | 27 +++++++++--------
 src/sys/s7.s | 18 +++++------
 3 files changed, 67 insertions(+), 64 deletions(-)

diff --git a/src/sys/s1.s b/src/sys/s1.s
index 80bc1c0..8dcf364 100644
--- a/src/sys/s1.s
+++ b/src/sys/s1.s
@@ -21,61 +21,61 @@ orig:
    jmp 1f+1
    1f
 1: 0
-   iof
-   dac u.ac
+   iof				" interrupts off
+   dac u.ac			" save user AC
    lacq
-   dac u.mq
+   dac u.mq			" save user MQ
    lac 8
-   dac u.rq
+   dac u.rq			" save user auto-index location 8
    lac 9
-   dac u.rq+1
-   jms copy; 10; u.rq+2; 6
-   lac 1b
-   dac u.rq+8
+   dac u.rq+1			" save user auto-index location 9
+   jms copy; 10; u.rq+2; 6	" save user auto-index locations 10-15
+   lac 1b			" load user PC after system call
+   dac u.rq+8			" save user PC
+   -1				" load -1
+   dac .savblk			" set "save" flag (cleared by disk I/O?)
+   dac .insys			" set "in system" flag
+   lac uquant			" load user quantum count
+   jms betwen; d0; maxquant	" check if between 0 & maxquant??
+      jms swap			" no: swap processes
+   ion				" interrupts on
    -1
-   dac .savblk
-   dac .insys
-   lac uquant
-   jms betwen; d0; maxquant
-      jms swap
-   ion
-   -1
-   tad u.rq+8
-   jms laci
-   jms betwen; o20001; swn
-      jmp badcal
-   tad swp
-   dac .+1
-   jmp .. i
+   tad u.rq+8			" get address of system call
+   jms laci			" load AC indirect??
+   jms betwen; o20001; swn	" range check
+      jmp badcal		" bad system call
+   tad swp			" add system call table base
+   dac .+1			" save as next instruction
+   jmp .. i			" dispatch system call
 
 . = orig+0100
    jmp coldentry
    jms halt
 
 okexit:
-   dzm: u.ac
-sysexit:
-   ion
-   lac .savblk
-   sza
-   jmp 1f
-   jms copy; sysdata; dskbuf; 64
+   dzm u.ac			" 'OK' system call exit: clear user AC
+sysexit:			" common system call exit code
+   ion				" enable interrupts
+   lac .savblk			" load "save" flag
+   sza				" is zero (cleared by disk I/O)?
+   jmp 1f			" no: no disk I/O done?
+   jms copy; sysdata; dskbuf; 64 " copy system data to disk buffer
    cla
-   jms dskio; 07000
+   jms dskio; 07000		" save to disk?
 1:
-   dzm .insys
+   dzm .insys			" clear "in system call" flag
    jms chkint
       skp
-   jmp .save
-   jms copy; u.rq+2; 10; 6
-   lac u.rq+1
+   jmp .save			" dump core??
+   jms copy; u.rq+2; 10; 6	" restore auto-index locations 10-15
+   lac u.rq+1			" restore auto-index location 9
    dac 9
-   lac u.rq
+   lac u.rq			" restore auto-index location 8
    dac 8
-   lac u.rq
+   lac u.mq			" restore MQ register
    lmq
-   lac u.ac
-   jmp u.rq+8 i
+   lac u.ac			" restore AC register
+   jmp u.rq+8 i			" return to user
 
 swap: 0
    ion
@@ -129,21 +129,21 @@ swap: 0
    jmp swap i
 t = t+1
 
-swp:
-   jmp .
+swp:			" system call dispatch table
+   jmp .		" base instruction
    .save; .getuid; .open; .read; .write; .creat; .seek; .tell
    .close; .link; .unlink; .setuid; .rename; .exit; .time; .intrp
    .chdir; .chmod; .chown; badcal; .sysloc; badcal; .capt; .rele
    .status; badcal; .smes; .rmes; .fork
 swn:
-   .-swp-1 i
+   .-swp-1 i		" count of system calls, plus indirect!
 
 .intrp:
    lac u.ac
    dac u.intflg
    jmp okexit
 
-.sysloc:
+.sysloc:		" "sysloc": syscall to return system addresses
    lac u.ac
    and o17777
    jms betwen; d1; locn
@@ -154,7 +154,7 @@ swn:
    dac u.ac
    jmp sysexit
 
-locsw:
+locsw:			" table of system data structures for "sysloc" call
    lac .
    iget; inode; userdata; sysdata; copy; copyz; betwen; dskrd
    dskwr; dskbuf; dpdata; namei; pbsflgs; alloc; free; dspdata
diff --git a/src/sys/s2.s b/src/sys/s2.s
index 9d7af58..3424c44 100644
--- a/src/sys/s2.s
+++ b/src/sys/s2.s
@@ -53,9 +53,9 @@
    jms iput
    jmp okexit
 
-.getuid:
+.getuid:			" getuid system call
    lac u.uid
-   dac u.ac
+   dac u.ac			" return u.uid in user AC
    jmp sysexit
 
 .seek:
@@ -146,12 +146,12 @@
    jms iput
    jmp sysexit
 
-.setuid:
-   lac u.uid
-   sma
-   jms error
-   lac u.ac
-   dac u.uid
+.setuid:			" setuid system call
+   lac u.uid			" load current user id
+   sma				" negative?
+   jms error			" no: error!!
+   lac u.ac			" load user AC
+   dac u.uid			" save as new uid
    jmp sysexit
 
 .rename:
@@ -168,11 +168,14 @@
    jms copy; 1:0; d.name; 4
    jmp okexit
 
+	" time system call returns line (mains) frequency ticks since boot?
+	" note: returns uptime!?
+	" at 60Hz, 36 bits would last 36+ years!
 .time:
-   lac s.tim
-   dac u.ac
-   lac s.tim+1
-   dac u.mq
+   lac s.tim			" load high order bits
+   dac u.ac			" return in AC
+   lac s.tim+1			" load low order bits
+   dac u.mq			" return in MQ
    jmp sysexit
 
 .chdir:
diff --git a/src/sys/s7.s b/src/sys/s7.s
index c5b307b..46e53ac 100644
--- a/src/sys/s7.s
+++ b/src/sys/s7.s
@@ -1,7 +1,7 @@
 "** 01-s1.pdf page 41
 " s7
 
-pibreak:
+pibreak:			" priority interrupt processing "chain"
    dac .ac	"** CROSSED OUT....
 
    dpsf
@@ -25,15 +25,15 @@ pibreak:
    dac dpwrite
    jmp piret	"** END OF CROSSOUT
 
-1: clsf
-   jmp 1f
+1: clsf			" clock overflow (line frequency ticks)?
+   jmp 1f		"  no
 
-   lpb
-   dac pbsflgs
-   isz s.tim+1
-   skp
-   isz s.tim
-   isz uquant
+   lpb			" load display push buttons
+   dac pbsflgs		" save
+   isz s.tim+1		" increment low order tick count
+   skp			"  no overflow, skip second increment
+   isz s.tim		"   low order overflowed, increment high order count
+   isz uquant		"    increment user quantum counter
 	"** written: ttydelay -> ttyd1
 	"** written: ttyrestart -> ttyres1
 cnop:

From 249ce47e44082cc57a76c8cba096b39313135dcf Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Mon, 29 Feb 2016 14:24:37 -0500
Subject: [PATCH 4/6] OR syllables by default (allows multiple OPR
 instructions)

---
 tools/as7 | 125 ++++++++++++++++++++++++++++--------------------------
 1 file changed, 66 insertions(+), 59 deletions(-)

diff --git a/tools/as7 b/tools/as7
index 2a4b958..943121b 100755
--- a/tools/as7
+++ b/tools/as7
@@ -4,7 +4,7 @@
 # and convert them into PDP-7 machine code
 #
 # (c) 2016 Warren Toomey, GPL3
-# Tweaked by Phil Budne (expression parsing, "list" format)
+# Tweaked by Phil Budne (line, expression parsing, "list" format)
 #
 use strict;
 use warnings;
@@ -25,7 +25,6 @@ my $origline;  # The original current input line of code
 my $line;      # line being parsed
 my $stage = 1; # Pass one or pass two
 my $errors = 0; # set to non-zero on error
-my %Undef;	# undefined symbols: only complain once
 my $line_error = ' ';
 my $file;	# current file name
 my $lineno;	# current line number
@@ -149,7 +148,7 @@ usage() if ( @ARGV < 1 );
     rsb    => 0700144,		# select PTR in binary mode
 
     psf    => 0700201,		# skip if PTP flag set
-    pcf    => 0700202,		# clear PTP clag
+    pcf    => 0700202,		# clear PTP flag
     psa    => 0700204,		# punch PTP in alphanumeric mode
     psb    => 0700244,		# punch PTP in binary mode
 
@@ -157,7 +156,7 @@ usage() if ( @ARGV < 1 );
     krb    => 0700312,		# read KBD buffer
     iors   => 0700314,		# input/output read status
 
-    tsf    => 0700401,		# if if TTY output flag set
+    tsf    => 0700401,		# skip if if TTY output flag set
     tcf    => 0700402,		# clear TTY output flag
     tls    => 0700406,		# load TTY output buffer and select
 
@@ -272,8 +271,9 @@ sub parse_file {
     close($IN);
 }
 
-# process a label and set its value to the location counter (only called on pass 1)
-# (if called on pass 2, should check if values are identical)
+# process a label and set its value to the location counter
+# only called on pass 1;
+# if called on pass 2, should check if values are identical
 sub process_label {
     my $label = shift;
 
@@ -294,25 +294,21 @@ sub process_label {
 }
 
 # Blame Phil for this....
-# parses global $line based on prefixes
-# (nibbling of a bit at a time)
+# parses global $line based on prefixes, nibbling of a bit at a time
+# (: and ; can appear in char literals)
 # handles multiple ';' separated words per line
 sub parse_line {
-    $line_error = ' ';
-    
+    # Lose any leading whitespace
+    $line =~ s{^\s*}{};
+
     while (1) {
-	# Lose any leading whitespace
-	$line =~ s{^\s*}{};
+	$line_error = ' ';	# clear listing error indicator
+
+	return if ($line eq '' || $line =~ m{^"}); # empty or comment: quit
 
 	print "parse_line: '$line'\n" if ($debug);
 
-	return if ($line eq '');
-
-	if ($line =~ m{^"}) { # remainder of line is comment
-	    return;
-        }
-
-	if ($line =~ s{^([a-z0-9\.]+):}{}) { # label
+	while ($line =~ s{^([a-z0-9\.]+):\s*}{}) { # labels
 	    my $label = $1;
 
             # First pass: parse the labels
@@ -321,44 +317,40 @@ sub parse_line {
 		process_label($1);
 	    }
 	}
-	else {
-	    my $lhs = undef;
-	    if ( $line =~ s{^(\S+)\s*=}{}) { # assignment
-		$lhs = $1;
-            }
+
+	if ( $line =~ s{^(\S+)\s*=}{}) { # assignment
+	    my $lhs = $1;
 	    my $word = parse_expression();
-	    if ($lhs) {
-	        printf( "Setting variable %s to 0%o\n", $lhs, $word ) if ($debug);
-	        $Var{$lhs} = $word;
-	        printf("\t%06o %s\n", $word, $line_error) if ($stage == 2 && $format eq 'list');
-	    }
-	    else {	# bare expression
-		# Get its value on pass two and save to memory
-		# Also save the input line that altered memory
-		if ( $stage == 2 ) {
-		    my $location  = $Var{'.'};
-		    $Mem[$location]   = $word;
-		    $Mline[$location] = $origline;
-		    $origline = '';
-		    if ($format eq 'list') {
-			printf( "%06o: %06o %s\n", $location, $word, $line_error);
-		    }
+	    printf( "Setting variable %s to 0%o\n", $lhs, $word ) if ($debug);
+	    $Var{$lhs} = $word;
+	    printf("\t%06o %s\n", $word, $line_error) if ($stage == 2 && $format eq 'list');
+	}
+	else {	# bare expression
+	    # Get its value on pass two and save to memory
+	    # Also save the input line that altered memory
+	    my $word = parse_expression();
+	    if ( $stage == 2 ) {
+		my $location  = $Var{'.'};
+		$Mem[$location]   = $word;
+		$Mline[$location] = $origline;
+		$origline = '';
+		if ($format eq 'list') {
+		    printf( "%06o: %06o %s\n", $location, $word, $line_error);
 		}
-		# Move up to the next location in both passes
-		$Var{'.'}++;
-	    } # expr
-        } # assignment or expression
+	    }
+	    # Move up to the next location in both passes
+	    $Var{'.'}++;
+	} # expr
 
 	# eat trailing whitespace and ";", if any
-	$line =~ s{^\s*}{};
-	$line =~ s{^;}{};
+	$line =~ s{^\s*;?}{};
     } # while
 }
 
 # Blame Phil for this bit too...
 # Parse an expression off $line and return a PDP-7 word
 # as a series of whitespace separated "syllables"
-# and adds them together.
+# ORed, added, or subtracted
 sub parse_expression {
     my $word = 0;
 
@@ -366,23 +358,22 @@ sub parse_expression {
 
     while (1) {
 	my $syllable = 0;
-	my $sign = 1;
+	my $op = '|';
 
 	$line =~ s{^\s+}{};
-	print "    '$line'\n" if ($debug);
 
 	if ($line eq '' || $line =~ m{^[";]}) { # EOL ; and " terminate expr
 	    printf("\tparse_expression => %#o\n", $word) if ($debug);
 	    return $word;
 	}
 
+	print "    '$line'\n" if ($debug);
+
 	if ($line =~ s{^-}{}) {
-	    # leading '-' negates upcomming syllable.
-	    $sign = -$sign;
+	    $op = '-';
 	}
-	else {
-	    # ignore leading '+'
-	    $line =~ s{^\+}{};
+        elsif ($line =~ s{^\+}{}) {
+	    $op = '+';
 	}
 
 	if ($line =~ s{^<(.)}{}) { # <char
@@ -406,8 +397,7 @@ sub parse_expression {
 		printf("\tlbl: %s: %#o\n", $sym, $syllable) if ($debug);
 	    }
 	    elsif ($stage == 2) {
-		err('U', "$sym not defined") unless (defined $Undef{$sym});
-		$Undef{$sym} = 1; # only complain once
+		err('U', "$sym not defined")
 	    } # pass 2
 	} # symbol
 	elsif ( $line =~ s{^(\d+)([fb])}{} ) { # relative label
@@ -421,14 +411,31 @@ sub parse_expression {
 	    else {
 		$syllable = $value + 0;
 	    }
+	    $syllable &= 0777777;
 	}
 	else {
+	    # From the BSD fortune file:
+	    # Ken Thompson has an automobile which he helped design.
+	    # Unlike most automobiles, it has neither speedometer,
+	    # nor gas gauge, nor any of the numerous idiot lights
+	    # which plague the modern driver. Rather, if the driver
+	    # makes any mistake, a giant "?" lights up in the center
+	    # of the dashboard. "The experienced driver",
+	    # he says, "will usually know what's wrong.
 	    err('?', "huh? '$line'");
-	    $line = '';
+	    $line = '';		# abort processing
 	    return $word;
 	}
-	$syllable = ($syllable * $sign) & 0777777;
-	$word = ($word + $syllable) & 0777777;
+	if ($op eq '+') {
+	    $word += $syllable;
+	}
+	elsif ($op eq '-') {
+	    $word -= $syllable;
+	}
+	else {
+	    $word |= $syllable;
+	}
+	$word &= 0777777;
 	printf("\tsyllable: %#o word: %#o\n", $syllable, $word) if ($debug);
     }
 }

From 8bd39e92471951b0909604aa82d28187d201110e Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Mon, 29 Feb 2016 14:27:34 -0500
Subject: [PATCH 5/6] add missing ;

---
 scans/trysys.s | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scans/trysys.s b/scans/trysys.s
index 029db17..90f429a 100644
--- a/scans/trysys.s
+++ b/scans/trysys.s
@@ -32,7 +32,7 @@ error:
 1: 077012
 
 a.out:
-   <a.>;<ou><t 040; 040040
+   <a.>;<ou>;<t 040; 040040
 t1: 0
 t2: 0
 c1: 0

From d8c7ba5179f8bf64709fa22ddeca8aa0fc3ab5d4 Mon Sep 17 00:00:00 2001
From: Phil Budne <phil@ultimate.com>
Date: Mon, 29 Feb 2016 14:28:03 -0500
Subject: [PATCH 6/6] fix typos

---
 scans/s1.s | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scans/s1.s b/scans/s1.s
index 80bc1c0..7a0ee42 100644
--- a/scans/s1.s
+++ b/scans/s1.s
@@ -53,7 +53,7 @@ orig:
    jms halt
 
 okexit:
-   dzm: u.ac
+   dzm u.ac
 sysexit:
    ion
    lac .savblk
@@ -72,7 +72,7 @@ sysexit:
    dac 9
    lac u.rq
    dac 8
-   lac u.rq
+   lac u.mq
    lmq
    lac u.ac
    jmp u.rq+8 i