Re: TIMI

[Blair Wyman <wyman@xxxxxxxxxxxx>]

Excerpts from midrange-l: 13-Jan-98 TIMI "David Prowak"@emi.com (442*) 

> During a Lunch & Learn earlier today, there was mention of the 
> TIMI (Technology Independent Machine Interface). 
> What is this? 
> What is it used for? 

The best place, IMO, to read about the TIMI is in Frank Soltis' book
"Inside the AS/400", but here's the nickel tour (and overpriced at that
:) 

The TIMI (internally known as 'the MI') is the functional definition of
the AS/400 'machine.'  If you write an MI assembler program, you are
writing to the TIMI. 

One of the TIMI's key attributes is that, unlike most machine
interfaces, it is not executable.  That is to say, the TIMI is the
'assembly language' (machine) interface for the AS/400 (the lowest-level
programming interface available to the programmer) and it does not
depend on the underlying technology (i.e. how many registers? ...how
wide are they?  ...are there memory mapped I/O addresses?).  So, the
TIMI representation has to be converted into actual hardware
instructions, but this is a function of the machine (and is performed by
the CRTPG TIMI instruction for OPM programs, and various TIMI
instructions such as CRTMOD, CRTBPG, etc. for ILE programs.) 

It was exactly the abstract technology-independent nature of the TIMI
that permitted us to put RISC processors in AS/400s in V3R6 without
requiring you to recompile your programs from source.  The TIMI
representation of the program *is* its 'observability,' and when it is
present it allows us to re-generate the actual hardware instructions
(the technology-dependent part of the program) without requiring you to
intervene. 

Anyway, that's the nickel tour.  Again, I recommend Frank Soltis' book
to get the real low-down...  Or, I can probably create some more
tortuously strange sentences if you think it'd help.  *8-) 

-blair 

  ___   _           Blair Wyman                  IBM Rochester 
 ( /_)  /  _  ' _   (507)253-2891           wyman@vnet.ibm.com 
__/__)_/_<_/_/_/_'  Opinions expressed may not be those of IBM. 

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