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1.1       root        1: .TH MEM 4
                      2: .CT 2 sa
                      3: .SH NAME
                      4: mem, kmem, kUmem, mtpr, fineclock \- memory and VAX processor registers
                      5: .SH DESCRIPTION
                      6: .lg
                      7: .I Mem
                      8: is a file that is an image of the main memory
                      9: of the computer.
                     10: It may be used to examine
                     11: (and even to patch) the system.
                     12: Byte addresses in
                     13: .I mem
                     14: are interpreted as physical memory addresses.
                     15: References to non-existent locations return errors.
                     16: .PP
                     17: .IR Kmem
                     18: and
                     19: .I kUmem
                     20: are like
                     21: .IR mem ,
                     22: but access kernel-mode virtual memory.
                     23: .I KUmem
                     24: promises that reads and writes will be done
                     25: in two-byte quantities;
                     26: this is convenient for UNIBUS accesses.
                     27: .PP
                     28: .I Mtpr
                     29: accesses
                     30: VAX internal processor registers.
                     31: Each register is 4 bytes long;
                     32: register
                     33: .I n
                     34: may be read or written at address
                     35: .IR n \(**4.
                     36: .PP
                     37: .I Fineclock
                     38: reads a high-resolution clock.
                     39: Reading four bytes returns a 32-bit unsigned integer
                     40: representing the number of microseconds since
                     41: the epoch 00:00:00 GMT, Jan. 1, 1970,
                     42: with high-order bits discarded.
                     43: .PP
                     44: .IR Mem ,
                     45: .IR kmem ,
                     46: .IR kUmem ,
                     47: and
                     48: .IR mtpr
                     49: have minor device numbers
                     50: 0, 1, 3, and 5.
                     51: .I Fineclock
                     52: is a separate driver;
                     53: the minor device number is ignored.
                     54: .SH FILES
                     55: .EX
                     56: .F /dev/mem
                     57: .F /dev/kmem
                     58: .F /dev/kUmem
                     59: .F /dev/mtpr
                     60: .F /dev/fineclock
                     61: .EE
                     62: .SH SEE ALSO
                     63: .IR time (2)
                     64: .br
                     65: VAX Hardware Handbook
                     66: .SH BUGS
                     67: Examining and patching device and processor registers may
                     68: give unexpected results when read-only or write-only
                     69: bits are present.
                     70: .br
                     71: An attempt to read a nonexistent processor register
                     72: returns 0
                     73: instead of an error.
                     74: .br
                     75: The
                     76: .I fineclock
                     77: counter overflows every hour or so.
                     78: It is only as precise as the hardware;
                     79: hence it is inaccurate on a MicroVAX.

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