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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/s1.s
+21 -17
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@@ -6,12 +6,16 @@ orig:
hlt " overwritten with interrupt return addr
jmp pibreak " dispatch to interrupt processing
. = orig+7
-1 " only ever set (to -1): never read?!
. = orig+7 " real time (60Hz) clock
-1 " -1 will cause "clock overflow" on next tick
" Overflow is checked by "clsf" instr
" in PI service (pibreak) routine,
" reset to -1 after tick handling
" results in an interrupt every "jiffy"
. = orig+020 " syscall (CAL) and user "interrupt" processing
1f " addr for "CAL I": store return here on "CAL"
iof " interrupts off
iof " here on CAL: interrupts off
dac u.ac " save user AC
lac 020 " save user return addr
dac 1f " save as if "CAL I"
@@ -22,29 +26,29 @@ orig:
1f " literal to restore location 20
1: 0 " "CAL I" PC stored here
iof " interrupts off
dac u.ac " save user AC
dac u.ac " save user AC in user area
lacq
dac u.mq " save user MQ
dac u.mq " save user MQ in user area
lac 8
dac u.rq " save user auto-index location 8
dac u.rq " save user auto-index location 8 in uarea
lac 9
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
dac u.rq+1 " save auto-index location 9 in user area
jms copy; 10; u.rq+2; 6 " save auto-index locations 10-15 (using 8/9!)
lac 1b " load user PC
dac u.rq+8 " save in user area
-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
lac uquant " load user quantum (tick) count
jms betwen; d0; maxquant " check if between 0 & maxquant (30 jiffies)
jms swap " no: quantum expired: swap process out
ion " interrupts on
-1
tad u.rq+8 " get address of system call
jms laci " load AC indirect??
jms betwen; o20001; swn " range check
jms laci " load system call instruction
jms betwen; o20001; swn " range check (expects CAL I!)
jmp badcal " bad system call
tad swp " add system call table base
tad swp " add "jmp syscall_table_base"
dac .+1 " save as next instruction
jmp .. i " dispatch system call
@@ -137,7 +141,7 @@ swp: " system call dispatch table
.chdir; .chmod; .chown; badcal; .sysloc; badcal; .capt; .rele
.status; badcal; .smes; .rmes; .fork
swn:
.-swp-1 i " count of system calls, plus indirect!
.-swp-1 i " last system call number: "CAL I n"
" AC/ new value for intflg (non-zero to ignore interrupt char)
" sys intrp