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DragonFly users List (threaded) for 2005-06
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Re: Historical use of "traps"

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 9 Jun 2005 09:32:51 -0700 (PDT)

:I was wondering about the historical meaning of the word "trap" today, 
:in context of hardware and software traps.  I have learned that creating 
:a trap generally means an interrupt is created by one means or another. 
:  So, does "trap" mean "a trap for the kernel to fall into and handle?"

    We need a historian.  I do remember that on the 6502 instruction code
    00 was a BRK instruction.  People would often use this to insert hooks 
    into eproms or proms without erasing them.  Simply program the location
    to 00 and it would trap into software which would then implement the

    In modern times TRAPs, EXCEPTIONS, and INTERRUPTs are nearly the same,
    except that TRAPs typically mean synchronous entry into the supervisor
    context (e.g. TRAP instruction), EXCEPTIONS mean (usually) synchronous
    entry into a theupervisor due to an instruction fault, and INTERRUPTs 
    mean asynchronous entry into the supervisor.

					Matthew Dillon 

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