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Annotation of 43BSDTahoe/man/man4/tahoe/mem.4, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1986 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)mem.4       6.2 (Berkeley) 6/30/87
        !             6: .\"
        !             7: .TH MEM 4 "June 30, 1987"
        !             8: .UC 7
        !             9: .SH NAME
        !            10: mem, kmem, vmem \- main memory
        !            11: .SH DESCRIPTION
        !            12: .lg
        !            13: .I Mem
        !            14: is a special file that is an image of the main memory
        !            15: of the computer.
        !            16: It may be used, for example, to examine
        !            17: (and even to patch) the system.
        !            18: .PP
        !            19: Byte addresses in
        !            20: .I mem
        !            21: are interpreted as physical memory addresses.
        !            22: References to non-existent locations cause errors to be returned.
        !            23: .PP
        !            24: Examining and patching device registers is likely
        !            25: to lead to unexpected results when read-only or write-only
        !            26: bits are present.
        !            27: .PP
        !            28: The file
        !            29: .I kmem
        !            30: is the same as 
        !            31: .I mem
        !            32: except that kernel virtual memory
        !            33: rather than physical memory is accessed.
        !            34: .PP
        !            35: The file
        !            36: .I vmem
        !            37: allows access to the mapped portion of the VERSAbus
        !            38: i/o space.  On the Tahoe the upper megabyte
        !            39: of the physical address space is accessible through
        !            40: this file (0xfff00000 through 0xffffffff). 
        !            41: Accesses to the upper 64 kilobytes of
        !            42: the i/o space result in VERSAbus transfers with a
        !            43: 16-bit address (the offset in this region) and a
        !            44: ``non-privileged short i/o'' VERSAbus address modifier.
        !            45: Accesses to the remainder of the mapped region,
        !            46: result in VERSAbus transfers with a 24-bit address
        !            47: and a ``non-privileged standard'' VERSAbus address
        !            48: modifier.  This region is actually part of the region
        !            49: between 0xfeff0000 and 0xffff0000
        !            50: which generates VERSAbus transfers with a 24-bit address.
        !            51: Accesses to the remainder of the one gigabyte i/o space
        !            52: generate transfers that utilize a 32-bit address with
        !            53: a ``non-privileged extended'' address modifier.  Any
        !            54: 32-bit address generated by a cpu access to this part
        !            55: of the i/o space have the upper two bits zero; thus,
        !            56: for example, an access to physical address 0xfe000000
        !            57: causes the address 0x3e000000 to be supplied in the
        !            58: resultant VERSAbus read/write cycle.
        !            59: .PP
        !            60: On the Tahoe, the 
        !            61: per-process data for the current process
        !            62: begins at virtual address 0xbffff000.
        !            63: .SH FILES
        !            64: /dev/mem,
        !            65: /dev/kmem,
        !            66: /dev/vmm
        !            67: .SH BUGS
        !            68: Memory files are accessed one byte
        !            69: at a time, an inappropiate method for some
        !            70: device registers.

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