[TUHS] PDP-7 cat is working
Warren Toomey
wkt at tuhs.org
Tue Mar 1 19:07:54 AEST 2016
All, I've got the original PDP-7 cat working in my PDP-7 user-mode
simulator called "a7out". The cat.s source code and the a7out program are
in the Github repository in src/cmds and tools, respectively.
The repository is at https://github.com/DoctorWkt/pdp7-unix
The mailing list is at http://minnie.tuhs.org/pipermail/pdp7-unix/
I'm attaching the a.out assembly output as the as7 assembler in the
repository currently is not quite ready for cat.s.
To run the original cat, create a text file, e.g. echo hello > file1
$ ./a7out a.out file1
hello <- the output of the PDP-7 machine code
Cheers, Warren
P.S Thanks again to Norman for getting us the scans.
-------------- next part --------------
000000: 237777 lac 017777 i
000001: 540407 sad d4 " Skip if we have more than four argument words
000002: 600052 jmp nofiles " Only four argument words, so no arguments
000003: 217777 lac 017777 " Move five words past the argument word count
000004: 340406 tad d1 " so that AC points at the first argument
000005: 340407 tad d4 " and save the pointer in name
000006: 040010 dac name
000007: 000003 sys open; name:0; 0 " Open file, get fd back
000010: 000000
000011: 000000
000012: 741100 spa
000013: 600035 jmp badfile " Negative fd, exit with an error message
000014: 040301 dac fi " Save file descriptor in fi
000015: 100104 jms getc " Get a character in AC
000016: 540407 sad o4
000017: 600022 jmp 1f " Break the loop when we get a ctrl-D
000020: 100140 jms putc " Write the character on stdout
000021: 600015 jmp 1b " and loop back
000022: 200301 lac fi " Close the file descriptor in fi
000023: 000011 sys close
000024: 777774 -4
000025: 377777 tad 017777 i " Subtract 4 from the count of argument words
000026: 077777 dac 017777 i
000027: 540407 sad d4 " Is the value 4, i.e. no args left?
000030: 600064 jmp done " Yes, so exit
000031: 200010 lac name " Still an argument, so move up
000032: 340407 tad d4 " to the next filename argument
000033: 040010 dac name
000034: 600007 jmp loop " and loop back to cat this file
000035: 200010 lac name " Get the pointer to the filename
000036: 040041 dac 1f " Store it in 1f below
000037: 200410 lac d8 " Load fd 8 which is stderr
000040: 000005 sys write; 1:0; 4 " Write the four words of the filename
000041: 000000
000042: 000004
000043: 200410 lac d8
000044: 000005 sys write; 1f; 2 " and then write " ?\n"
000045: 000050
000046: 000002
000047: 600024 jmp loop1 " Now try doing the next argument
000050: 000040 1: 040;077012 " String literal: " ?\n"
000051: 077012
000052: 200410 lac d8
000053: 000005 sys write; 1f; 5 " Write "No files\n" to stderr
000054: 000057
000055: 000005
000056: 000016 sys exit " and exit
000057: 156157 1: <no>; 040; <fi>;<le>;<s 012
000060: 000040
000061: 146151
000062: 154145
000063: 163012
000064: 200404 lac noc " Is the number of characters left zero?
000065: 741200 sna
000066: 000016 sys exit " Yes, exit
000067: 500406 and d1
000070: 751200 sna cla
000071: 600074 jmp 1f
000072: 100140 jms putc " Print out the character
000073: 600064 jmp done " and loop back
000074: 200404 lac noc
000075: 744020 rcr
000076: 040102 dac 1f
000077: 200405 lac fo " Load fd 1, stdout
000100: 000005 sys write; iopt+1; 1:..
000101: 000304
000102: 000000
000103: 000016 sys exit
000104: 000000 getc: 0
000105: 200176 lac ipt " Load the pointer to the next word in the buffer
000106: 540177 sad eipt
000107: 600123 jmp 1f " We've reached the end of the buffer, so read more
000110: 040174 dac 2f " Save the pointer
000111: 300411 add o400000 " Flip the msb and save into ipt
000112: 040176 dac ipt
000113: 740010 ral " Move the msb into the link register
000114: 220174 lac 2f i " Load the word from the buffer
000115: 741400 szl " Skip if this is the second character in the word
000116: 660511 lrss 9 " It's the first char, shift down the top character
000117: 500412 and o177 " Keep the lowest 7 bits
000120: 741200 sna
000121: 600105 jmp getc+1 " Skip a NUL characters and read another one
000122: 620104 jmp getc i " Return the character from the subroutine
000123: 200301 lac fi " Buffer is empty, read another 64 characters
000124: 000004 sys read; iipt+1; 64
000125: 000201
000126: 000100
000127: 741200 sna
000130: 600136 jmp 1f " No characters were read in
000131: 340200 tad iipt " Add the word count to the base of the buffer
000132: 040177 dac eipt " and store in the end buffer pointer
000133: 200200 lac iipt " Reset the ipt to the base of the buffer
000134: 040176 dac ipt
000135: 600105 jmp getc+1 " and loop back to get one character
000136: 200407 lac o4 " No character, return with ctrl-D
000137: 620104 jmp getc i " return from subroutine
000140: 000000 putc: 0
000141: 500412 and o177 " Keep the lowest 7 bits and save into 2f+1
000142: 040175 dac 2f+1
000143: 200302 lac opt " Save the pointer to the empty buffer
000144: 040174 dac 2f " position to 2f
000145: 300411 add o400000 " Flip the msb and save back into opt
000146: 040302 dac opt " This also has the effect of incrementing
000147: 741100 spa " If the bit was set, we already have one
000150: 600154 jmp 1f " character at 2f+1. If no previous character,
000151: 220174 lac 2f i " merge the old and new character together
000152: 240175 xor 2f+1
000153: 600156 jmp 3f " and go to the "save it in buffer" code
000154: 200175 lac 2f+1 " Move the character up into the top half
000155: 660711 alss 9
000156: 060174 dac 2f i " Save the word into the buffer
000157: 440404 isz noc " Add 1 to the char count, never skipping
000160: 200404 lac noc " Have we reached 128 characters, 64 words?
000161: 540413 sad d128
000162: 741000 skp
000163: 620140 jmp putc i " No, so return (more room still in the buffer)
000164: 200405 lac fo " Load fd1 (i.e stdout)
000165: 000005 sys write; iopt+1; 64 " and write out the 64 words in the buffer
000166: 000304
000167: 000100
000170: 200303 lac iopt
000171: 040302 dac opt " Set opt pointing back to base of buffer
000172: 140404 dzm noc " Set the number of chars in the buffer to 0
000173: 620140 jmp putc i " and return
000174: 000000 2: 0;0 " Current input and output word pointers
000175: 000000
000176: 000000 ipt: 0 " Current input buffer base
000177: 000000 eipt: 0 " Pointer to end of data read in input buffer
000200: 000201 iipt: .+1; .=.+64 " 64 word input buffer and pointer to it
000301: 000000 fi: 0 " Input file descriptor
000302: 000304 opt: .+2 " Current output buffer base
000303: 000304 iopt: .+1; .=.+64 " 64 word output buffer and pointer to it
000404: 000000 noc: 0 " Number of output characters
000405: 000001 fo: 1 " Output file descriptor, fd 1 is stdout
000406: 000001 d1: 1 " Octal and decimal constants
000407: 000004 o4:d4: 4
000410: 000010 d8: 8
000411: 400000 o400000: 0400000 " Msb toggle bit
000412: 000177 o177: 0177 " ASCII mask
000413: 000200 d128: 128 " 128 words in the output buffer
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