Task Management

Task Manipulation Interface Functions

There are five functions that manipulate tasks;

• task_register()
• task_suspend()
• task_active()
• task_resume()
• task_sleep()

task_register() function registers a task with a specified priority. The priority defines how often the task gets actual execution time.

task_suspend() suspends a task. Suspended tasks never get execution time until they are resumed, by task_resume(), or activated, by task_active().

task_active() activates a task. Tasks activated by the function fall into ACTIVE state and get execution time as soon as possible.

task_resume() reschedules execution timing for a task taking the task priority, which is set by task_register(), into account.

task_sleep() sets a task SLEEPING status. Sleeping time duration can be specified in mili-seconds.

Task Switching and Task Priority

Actual task switching is made in the main() function. The switching timing is triggered by TIMER0 interrupt, which is set 2 mili-seconds. The next execution timing for a task is set by task_resume() function or just after the execution of the task in task switching routine, the main() function. The next execution timing for a task with priority p is defines as

    T = (p + 1) * t

where t is the task switching interval, 2 mili-seconds.

TIMER1 Interface

TIMER1 is used as a free incremental counter for time interval measurement. There are two interface functions, timer1_get_4usec() and timer1_get_1msec().

timer1_get_4usec() returns a counter value measured in 4 μ seconds.

timer1_get_1msec() returns a counter value measured in 1 mili-seconds.

LM1973 Attenuation Control

There are eight functions for attenuation control.

volume_set_volume() sets attenuation. The attenuation level, A dB, and the volume level passed to volume_set_volume(), V, is related as

    A = -0.5 * (50 - V)

where the volume level, V, can take 0 - 50.

volume_get_volume() returns current volume level.

volume_get_atten() returns current attenuation level. Note that the returned value is opposite signed value of actual attenuation level.

volume_up() increments volume level.

volume_down() decrements volume level.

volume_mute() mutes LM1973 output.

volume_unmute() unmutes LM1973 output.

volume_ckeck_mute() returns the status of LM1973; 0 is unmuted status and 1 is muted status.

EEPROM Interface

There are six functions to read and write EEPROM.

eeprom_read8() reads 1 byte data from the specified EEPROM address.

eeprom_read16() reads 2 byte data from the specified EEPROM address.

eeprom_read32() reads 4 byte data from the specified EEPROM address.

eeprom_write8() writes 1 byte data to the specified EEPROM address.

eeprom_write16() writes 2 byte data to the specified EEPROM address.

eeprom_write32() writes 4 byte data to the specified EEPROM address.

Seven Segment

Seven Segment control is achieved by a management task and three interface functions.

Seven Segment Management Task

The management task, task_sevensegment(), takes the roll of illuminating LED's. The task's priority is set the highest, '0', in the system (refer to "electricvolume.h").
Seven Segment has three display status: MUTE, NORMAL and BLINK. In the MUTE status Seven Segment blacks out. Seven Segment displays a two digit value normally in NORMAL status. In BLINK status, Seven Segment displays two digit value with blinking.

Seven Segment Interface Functions

ss_display_dec() displays a two digit decimal value. The value can take 0 to 99.

ss_display_hex() displays a two digit hexadecimal value. The value can take 0x00 to 0xFF.

ss_display_char() displays a two digit characters set associated to a specified value. The character sets are defined as

VALUE	CHARACTER SET	COMMENT
0	OF	OFF
1	On	ON
2	uP	UP
3	dn	DOWN
4	==	MUTE
5	P1	PRESET 1
6	P2	PRESET 2
7	P3	PRESET 3
8	P4	PRESET 4
9	P5	PRESET 5

Rotary Encoder

The Rotary encoder is controlled by a management task, task_rotaryencoder().
The management task

• keeps watching phase A signal of the rotary encoder, EC16B,
• checks phase B signal when phase A signal transit OFF=>ON, and finds out the rotation direction,
• increments or decrements volume level depending on the rotation direction, and
• updates the seven segment display.

IR Sensor

IR sensor control consists of a interrupt routine, a management task and four interface functions.

IR Interrupt Routine

The signal from the IR sensor, PL-IRM0101-3, is fed to RB7 pin of PIC16F88 and PORTB change interrupt is used to detect the change of IR signal. The IR interrupt routine checks ON=>OFF and OFF=>ON signal transition and

• measures OFF duration and ON duration,
• finds out LEADER, "1" or "0" signal, and
• saves received IR code and notifies to the IR Management Task when a datum is ready.

IR Management Task

The management task, task_infrared(), wakes up every 150 mili-seconds normally and controls volume level of LM1973 according to the received IR code. Because the system can learn which volume control function (UP, DOWN, MUTE or PRESET 1-5) is associated to an IR code, the management task simply compares 32 bit data and execute the associated function.

IR Interface Functions

ir_code_init() reads IR codes for volume control functions (UP, DOWN, MUTE and PRESET 1-5) from EEPROM.

ir_get_last_code() returns the 32 bit IR code received most recently.

ir_set_code() makes the association of a volume control function and a 32 bit IR code. The function saves the association information to EEPROM as well.

ir_set_preset() makes the association of a preset function and preset information (a 32 bit IR code and a volume level). The function saves the association information to EEPROM as well.

Push Button

Push button is controlled by a management task, task_pushbutton().
The management task controls two system status: NORMAL MODE and LEARNING MODE. When the system is in NORMAL MODE, the management task simply keeps watching the button status, waking up every 100 mili-seconds, and makes the system LEARNING MODE when the button is kept down (ON) for more than 3 seconds.

When the system is going into LEARNING MODE, the management task suspends IR management task.

In the LEARNING MODE, the management task

1. displays the characters that indicates one of the volume control functions (UP, DOWN, MUTE and PRESET 1-5) to which an IR code is to associate,
2. associates the latest IR code received to the volume control function when the button is pushed down, and
3. repeats 1 and 2 for all volume control functions (UP, DOWN, MUTE and PRESET 1-5).

The system learns IR codes in a order of UP => DOWN => MUTE => PRESET 1 => .... => PRESET 5 functions. The volume control functions (UP, DOWN, MUTE and PRESET 1-5) to learn transits one by one as the button is pushed down.

Since the management task takes the latest IR code received when learning an IR code, you can enter IR key pad multiple times before pushing the button.

For PRESET 1-5 functions, a volume level is read and saved with an IR code. Volume level can be varied by turning the rotary encoder.

When returning to NORMAL MODE after finishing learning IR codes, the management task resumes IR management task.