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Improve sys annotations

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Finally understand location 7 (incremented at 60Hz)
	setting it to -1 causes clock interrupt every jiffy
Improve comments in dsktrans
Clarify cnop/cskp usage in iread/iwrite code
	iwrite and iread have common code
	entry at iwrite save return address at iread
		and overwrites return address to "skp" inst
	entry at iread puts "nop" inst at iwrite
	"xct iwrite" skips on write entry
This commit is contained in:
phil
2019-10-21 22:24:09 -04:00
parent 17c9581351
commit 4b284c6bbe
5 changed files with 63 additions and 59 deletions
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src/sys/s7.s
+12 -11
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@@ -25,23 +25,24 @@ pibreak: " priority interrupt break processing "chain"
dac dpwrite " dpwrite = -1
jmp piret "** END OF CROSSOUT
1: clsf " clock overflow (line frequency ticks)?
1: clsf " clock overflow (60hz tick increment of loc 7 (-1))
jmp 1f " no
lpb " load display push buttons
dac pbsflgs " save
isz s.tim+1 " increment low order tick count
skp " no overflow, skip second increment
skp " no overflow, skip high order word increment
isz s.tim " low order overflowed, increment high order count
isz uquant " increment user quantum counter
"** written: ttydelay -> ttyd1
" ("never" skips: 36 bits overflows every 36 years!)
isz uquant " increment user quantum counter (ignore overflow)
" (18 bits overflows in 72 minutes)
"** written: ttydelay -> ttyd1 ;
"** written: ttyrestart -> ttyres1
cnop: " fetched as constant in iread
nop
cnop: " constant location for iread (stored at iwrite!)
nop
-1
dac 7 " set location 7 to -1 (nothing ever checks/clears it?)
clon " enable clock interrupts, reset flag
dac 7 " reset rt clock count to -1 (overflow on next tick)
clon " enable clock interrupts, clear overflow flag
lac ttydelay " tty delay positive?
spa " yes: skip to skp
isz ttydelay " no: done delaying?
@@ -129,7 +130,7 @@ dsprestart:
jmp piret " no: done
lac sfiles+1 " get ttyout sleep word
sma " highest bit set?
xor o400000 " no, make it so (why???)
xor o400000 " no, make it so
dac sfiles+1 " save back
"** 01-s1.pdf page 43
@@ -168,7 +169,7 @@ ttyrestart: 0
tad o20 " bump by 16
rcr " divide by two
cma " complement
dac ttydelay " save
dac ttydelay " save as delay countdown
jmp ttyrestart i
2:
lac sfiles+1 " run out of characters to send: wake user(s)