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MULTITASKING SUMMARY
AVAILABILITY
One form of multitasking is available on the TDS9092 embedded
computer. If you need a full pre-emptive multitasker, look at the TDS2020F
computer.
q
Interrupt Multitasking
where an interrupt swaps the Forth system for a new one at regular intervals,
runs one pass through a high level Forth word and then returns, so forming a
background loop. This is a standard feature of TDS9092 in the Forth ROM.
In addition, high level Forth code can be attached to any interrupt,
whether internal or external.
MULTITASKING WORDS
This is a list of words defined within the Forth ROM and files
_TIMING.TDS and _EVERY.TDS which are available for use in application programs
which require multitasking.
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ASSIGN
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( addr - )
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Used at compile-time only to allow a Forth word to be
executed on interrupt or as a regular background task. See pages
90-95. E.g. OCI ASSIGN RINGER
associate RINGER with
output compare interrupt of 16-bit timer)
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DELAY
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( d - )
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Delay by 32-bit number d units. 1 unit=814ns
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EVERY
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( d - )
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Perform following word every d tenths of a second. Maximum
that can be used is 1638.3 secs (27 mins). d is a 32-bit number
but only lower 16 bits used. Application is background execution of one
or many programs at defined time intervals. E.g. Run routine
AAAA every 100ms, BBBB every second and
CCCC each minute.
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LATER
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( u - )
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Used in interrupt multitasking to specify that the word
it is included in should be run again u timeslots later. 1 slot=814ns.
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LONG
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( - addr )
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A variable forming a 16-bit extension to the 16-bit
free-running timer.
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LONGER
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( - addr )
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A variable forming a 16-bit extension to
LONG
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MS
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( u - )
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Delay by 1 to 65535 milliseconds. The Forth ROM version
is based on software loops but the redefinition in _TIMING.TDS gives real-time.
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REAL
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( - t )
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Returns real time as 48-bit 2s complement no. Each
unit is 814ns; there are 1228800 per second. 32-bit counter overflows
every 58 mins 15.253 secs, 48-bit counter overflows every 7 years
95 days E.g. REAL DROP gives
a double number repeating every 58mins
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RETURN;
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( - )
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Used instead of ; to end a high level Forth word which
is to execute on interrupt and which will be the subject of an
ASSIGN statement. See INTERRUPTS.
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