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| multitasking.h |
Description:
Allow
an easy way to program tasks that must be executed periodically.
In a wide meant this helps to do time based programming.
Timer0 is used to generate an interrupt with a period determined by base_time
,for each task a counter is increased until the predefined
task-time value is reached, then sets a task-flag that indicates the
task can be executed.
This library is included in GcBasic-PL installer, but you can download
it directly: multitasking.h
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Use:
Actually a
maximum of 16 Tasks and 8 LTasks are supported.
The base time must be defined:
#define base_time value
where value is the desired period in us, for example:
#define
base_time 100
' for 100 us
Maximum base_time value with 20 MHz clock is 13107.
Maximum base_time value with 4 MHz clock is 65535.
Maximum base_time value with other clocks: 65535/ChipMhz/4.
The subroutine containing each task must be defined:
#define Task1 Sub_name1
#define Task2 Sub_name2
#define
LTask1 Sub_name3
The period of each Task must be defined, for example:
#define Task1_us 500
' Task1 period is 500 us
#define Task2_ms 10
' Task2 period is 10 ms
#define LTask1_s 1
' LTask1 period is 1 s
In this example, Sub_name1 will be executed every 500 us, Sub_name2
every 10 ms and Sub_name3 every 1 seg.
Maximum value for Task period in us is: base_time*255
For example, with a 100 us base_time, maximum value for Tasks is:
100*255 = 25500 us => 25 ms
LTask is for long period tasks, a period is long or not depending on
the base_time
When the needed period > base_time*255 then you need an LTask.
Maximun value for LTask period in us is: base_time*65535
For example, with a 100 us base_time, maximum value for LTasks is:
100*65535 = 6553500 us => 6553 ms => 6 s
Task will be executed with the command: Do_Taskx,
for example in a main loop:
do
Do_Task2
Do_LTask1
loop
or any other way... for example:
do
Do_Task2
if PORTB.0 on then Do_LTask1
loop
Is possible to execute a Task directly inside Interrupt subroutine:
#define Run_Task1
'Run Task inside interrupt subroutine
There is a counter variable for each task: cont_Taskx
A period
variable:
time_Taskx
And a task flag:
flag_Taskx
These variables can be used in the program, reading or writting to
achieve different behaivors; see next example where time_task3 variable
is used to have a variable period task.
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Example:
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'________________________________________________________________________________
'
'
Example for multitasking.h
'
'
'
One led atached to PORTB.0 toggles at 1 s rate
'
One led atached to PORTB.1 toggles at
300 ms s rate
'
One led atached to PORTB.3 toggles at
a variable rate, defined by ReadAD
'
'________________________________________________________________________________
'
#chip 16F876A, 20 'MHz
#config HS_OSC, WDT_OFF,
LVP_OFF, PWRTE_ON
'________________________________________________________________________________
#include
<multitasking.h>
#define base_time 500
'Base time in us
#define Task1 read_input
'Task1 subroutine
#define Task1_us 500
'This task will run every 500 us
#define Task2 led2
'Task2 subroutine
#define Task2_ms 300
'This task will run every 300 ms
#define Task3 led3
'Task3 subroutine
'We will have the period for this
task from ReadAD
#define LTask1 led1
'LTask1 subroutine
#define LTask1_s 1
'This task will run every 1 s
#define Run_LTask1
'Run Task inside interrupt subroutine
'________________________________________________________________________________
DIR PORTA.0 IN
DIR PORTB OUT
do
'Main Loop
Do_Task1
Do_Task3
Do_Task2
loop
'________________________________________________________________________________
Sub read_input
time_Task3
= ReadAD(An0)
'Read ADC
at PORTA.0
End Sub
Sub led1
PORTB
= PORTB xor
1 'Toggle led at PORTB.0
End Sub
Sub led2
PORTB
= PORTB xor 2
'Toggle led at PORTB.1
End Sub
Sub led3
PORTB
= PORTB xor 4
'Toggle led at PORTB.2
End Sub
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