Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!linus!philabs!cmcl2!seismo!mcvax!euroies!rshepherd
From: rshepherd@euroies.UUCP (Roger Shepherd INMOS)
Newsgroups: net.arch,net.micro.mac,net.micro.68k
Subject: Re: timing loops
Message-ID: <200@euroies.UUCP>
Date: Thu, 20-Feb-86 09:46:29 EST
Article-I.D.: euroies.200
Posted: Thu Feb 20 09:46:29 1986
Date-Received: Mon, 24-Feb-86 07:25:43 EST
References: <221@myrias.UUCP>
Organization: University College Dublin
Lines: 24
Xref: linus net.arch:2387 net.micro.mac:4781 net.micro.68k:1440

Have a look at the transputer. Apart from a bug in REV A devices, all
transputers (no matter what speed selection) run of a standard (5 or 25 Mhz
) clock frequency. This is used to derive the standard comms link
speed and the processor clock. The transputer's real time
clock/alarm runs at 1 tick per micro-second at high priority,
this means that the occam program below will look at (eg) a uart
once every 5 uS. The accuracy achievable is quite good as the iunterrupt
latency (time to go from low to high priority) is about 58 cycles worst 
case (2.9 uS for a T414-20 - currently available parts are -12 so are
have 4.64 uS latency). 

PRI PAR
  SEQ 
    ... initialisation
    WHILE polling
      SEQ
        TIME ? AFTER nextinstance
        ... poll uart or whatever
        nextinstance := nextinstance + 5 -- 1 tick per uS
  ... -- rest of system at low priority
-- 
Roger Shepherd, INMOS Ltd, Whitefriars, Lewins Mead, Bristol, BS1 2NP, UK
Tel: +44 272 290861
UUCP: ...!mcvax!euroies!rshepherd