Back in their days, the TI 960 minicomputer (TTL
technology) used to have a crude OS (though they
*didn't* call it that) in the form of "PSM"  (Program
Support Monitor) and "PAM" (Program Automation
Monitior) - essentially a set of callable 'routines' linked
together (entries via a table) that handled peripherals and
some other tasks.

Routines to handle a CRT/Terminal, card reader, paper
tape reader, etc, as well 'calls' to do floating point operations
were the core of PSM or PAM.

Jim


----- Original Message -----
From: "wouter van ooijen & floortje hanneman" <wf@XS4ALL.NL>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, August 15, 2001 7:34 AM
Subject: Re: [EE]:Embedded system ,RTOS


> > Our RTOS, which is available for all PICmicro devices, is also
> > available in a freeware version called Salvo Lite. You may want to
> > download it and take it for a spin. The Salvo User manual has a
> > chapter dedicated to RTOS fundamentals -- not as in-depth as Jean
> > Labrosse's book, but a good starting point, and free for the
> > downloading.
>
> The main problem with any RTOS running on 12 and 14 bit PICs (including
> Salvo) is that a task switch can only occur in the main body of a task,
not
> in a called function. Think about the implications for a HD44780-LCD or
I2C
> library that has to wait between operations: it must either use a busy
wait
> (stalling the other tasks) or be in-lined in the main task (with grave
> consequences for the code size). I think I must agree with Olin: no
> accessible purpose stack? In that case an RTOS makes no sense. Note that a
> library of usefull routines might still make sense (an Salvo seems to fall
> in that category), but it is misleading to call it an RTOS. Note also that
> the size of the microcontroller (RAM, ROM, interrupt or not) has nothing
to
> do with it. It is just the fact that you can not stack-switch.
>
> Wouter van Ooijen
>
> van Ooijen Technische Informatica: http://www.xs4all.nl/~wf/
> Jal compiler for PIC microcontrollers:
http://www.xs4all.nl/~wf/wouter/jal
>
> --
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>
>

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