MEM(4) MEM(4)
NAME
mem, kmem, kUmem, mtpr, fineclock - memory and VAX processor
registers
DESCRIPTION
Mem is a file that is an image of the main memory of the
computer. It may be used to examine (and even to patch) the
system. Byte addresses in mem are interpreted as physical
memory addresses. References to non-existent locations
return errors.
Kmem and kUmem are like mem, but access kernel-mode virtual
memory. KUmem promises that reads and writes will be done
in two-byte quantities; this is convenient for UNIBUS
accesses.
Mtpr accesses VAX internal processor registers. Each regis-
ter is 4 bytes long; register n may be read or written at
address n*4.
Fineclock reads a high-resolution clock. Reading four bytes
returns a 32-bit unsigned integer representing the number of
microseconds since the epoch 00:00:00 GMT, Jan. 1, 1970,
with high-order bits discarded.
Mem, kmem, kUmem, and mtpr have minor device numbers 0, 1,
3, and 5. Fineclock is a separate driver; the minor device
number is ignored.
FILES
SEE ALSO
time(2)
VAX Hardware Handbook
BUGS
Examining and patching device and processor registers may
give unexpected results when read-only or write-only bits
are present.
An attempt to read a nonexistent processor register returns
0 instead of an error.
The fineclock counter overflows every hour or so. It is
only as precise as the hardware; hence it is inaccurate on a
MicroVAX.