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s4.s: comment disk block free and (self modifiying) char queue routines

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This commit is contained in:
Phil Budne
2016-04-15 00:52:26 -04:00
parent cb187e12be
commit c8129d7fa4
1 changed files with 106 additions and 92 deletions
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198
src/sys/s4.s
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@@ -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: