Smart Car Race
Layered architecture
The ability to provide a design of different levels of abstraction can



Simplify the design considerably
Enable different role players to effectively
Work at various levels of abstraction
Systems design and business process design can both use this. Some design processes specifically
generate designs that contain various levels of abstraction.
Layered architecture partitions the concerns of the application into stacked groups (layers). it is a
technique used in designing computer software, hardware, and communications in which system
or network components are isolated in layers so that changes can be made in one layer without
affecting the others.
Layers used in the Smart Car Race Project
APP
PID Position
HAL
Servo
Motor
Sensors
LCD/Buttons
PI Motors
MAL
ADC
eMIOS
GPIO
Motores
MAL (Microcontroller Abstraction Layer)
ADC
The analog-to-digital converter (ADC) block provides accurate and fast conversions
for a wide range of applications. An ADC module has a corresponding digital interface.
The ADC digital interface contains advanced features for normal or injected conversion. A
conversion can be triggered by software or hardware (Cross Triggering Unit or PIT).
There are three types of input channels:
• Internal precision, ADC0_P[n] (internally multiplexed precision channels)
• Internal standard, ADC0_S[n] (internally multiplexed standard channels)
• External ADC0_X[n] (externally multiplexed standard channels)
The mask registers present within the ADCDig can be programmed to configure which
channel has to be converted. Three external decode signals MA[2:0] (multiplexer address)
are provided for external channel selection and are available as alternate functions on
GPIO. The MA[0:2] are controlled by the ADC itself and are set automatically by the
hardware. A conversion timing register for configuring different sampling and conversion
times is associated to each channel type.
Normal conversion
This is the normal conversion that the user programs by configuring the normal
conversion mask register (NCMR). Each channel can be individually enabled by setting ‘1’
in the corresponding field of NCMR registers. Mask registers must be programmed before
starting the conversion and cannot be changed until the conversion of all the selected
channels ends (NSTART bit in the Main Status Register (MSR) is reset).
Normal Conversion Operating Modes
Two operating modes are available for the normal conversion:
• One Shot
• Scan
To enter one of these modes, it is necessary to program the MCR[MODE] bit. The first
phase of the conversion process involves sampling the analog channel and the next phase
involves the conversion phase when the sampled analog value is converted to digital.
In Scan Mode (MODE = 1), a sequential conversion of N channels specified in the
NCMR registers is continuously performed. As in the previous case, at the end of each
conversion the digital result of the conversion is stored into the corresponding data register.
The MSR[NSTART] status bit is automatically set when the Normal conversion starts.
Unlike One Shot Mode, the MCR[NSTART] bit is not reset. It can be reset by software
when the user needs to stop scan mode. In that case, the ADC completes the current scan
conversion and, after the last conversion, also resets the MSR[NSTART] bit.
ADC used in the Smart Car Race Project
Functions
For the Smart Car Race, we use 11 ADC channels in Scan Mode, each one for every
phototransistor of the sensor board. The idea is to multiplexing each sensor to obtain the analog
value to know which color is sensing the phototransistor. In the code we used 3 functions to
manipulate this Layer. The next Table 1.1 shows how the functions work.
Function
How it works
void ADC_init(void);
In this function, the ADC is configurated to
works in Scan Mode, setting the bit 2 of the
MCR (Main Configuration Register)
void ADC_paths(void);
Configuration of the paths in ADC mode
unsigned long ADC_shot(int lub_channel)
This function returns an unsigned long value
which is the ADC Conversion. In the argument,
the channel is declared by the user. This
function works very easy and it can be really
useful and powerful to work with.
Table 1.1- Functions and how they work.
Variables and #Defines
In the ADCHeader, we declared the variables used in this layer. The principal function of
the variables and defines is to have the possibility to make changes without change large lines of
code, it makes possible the portability. We know that we don’t need to make the code portable,
but we decide this just to show the rules and recommendations that were taught in the courses.
Macros and Variables
Name
Register or Constant
1. ADC_channel
Macro used to configure the Normal Conversion
Mask Register 0 (NCMR0). Sets the channel used
for conversion.
2. ADC_start
Macro used to configure the Normal
Convertion. Setting this bit starts the chain or
scan conversion.
3. ADCconfiguration
Macro used to configure the Main
Configuration Register (MCR). Sets the Mode of
operation.
4. ADCtimeConvertion
Macro used to configure the Conversion timing
registers. Sets the conversion time.
5. ADC_pad[1:11]
Macro used to configure the pads as ADC
function.
6. luw_channel
Stores the number of the channel that we want
to get the analog Value.
7. luw_potencia
Using an algorithm, this variable gets the
number of the channel, then we have to shift
the lub_potencia variable because our ADC
channel starts in the number 4 (ANP4).
8. lul_resultado
Stores the value of the ADC convertion.
eMIOS
The eMIOS provides functionality to generate or measure time events. The eMIOS
uses timer channels that are reduced versions of the unified channel (UC) module used on
MPC555x devices. Each channel provides a subset of the functionality available in the
unified channel, at a resolution of 16 bits, and provides a user interface that is consistent
with previous eMIOS implementations.
Modulus Counter (MC) mode
The MC mode can be used to provide a time base for a counter bus or as a general
purpose timer. Bit MODE[6] selects internal or external clock source when cleared or set,
respectively. When external clock is selected, the input signal pin is used as the source and
the triggering polarity edge is selected by the EDPOL and EDSEL in the EMIOSC[n] register.
The internal counter counts up from the current value until it matches the value in
register A1. Register B1 is cleared and is not accessible to the MCU. Bit MODE[4] selects
up mode or up/down mode, when cleared or set, respectively.
When in up count mode, a match between the internal counter and register A1
sets the FLAG and clears the internal counter. The timing of those events varies according
to the MC mode setup as follows:
• Internal counter clearing on match start (MODE[0:6] = 001000b)
o External clock is selected if MODE[6] is set. In this case the internal counter
clears as soon as the match signal occurs. The channel FLAG is set at the
same time the match occurs. Note that by having the internal counter
cleared as soon as the match occurs and incremented at the next input
event a shorter zero count is generated.
o Internal clock source is selected if MODE[6] is cleared. In this case the
counter clears as soon as the match signal occurs. The channel FLAG is set
at the same time the match occurs. At the next prescaler tick after the
match the internal counter remains at zero and only resumes counting on
the following tick.
• Internal counter clearing on match end (MODE[0:6] = 001001b)
o External clock is selected if MODE[6] is set. In this case the internal counter
clears when the match signal is asserted and the input event occurs. The
channel FLAG is set at the same time the counter is cleared.
o Internal clock source is selected if MODE[6] is cleared. In this case the
internal counter clears when the match signal is asserted and the prescaler
tick occurs. The channel FLAG is set at the same time the counter is cleared.
When in up/down count mode (MODE[0:6] = 00101bb), a match between the
internal counter and register A1 sets the FLAG and changes the counter direction from
increment to decrement. A match between register B1 and the internal counter changes
the counter direction from decrement to increment and sets the FLAG only if MODE[5] bit
is set. Only values different than 0x0 must be written at A register. Loading 0x0 leads to
unpredictable results. Updates on A register or counter in MC mode may cause loss of
match in the current cycle if the transfer occurs near the match. In this case, the counter
may rollover and resume operation in the next cycle. Register B2 has no effect in MC
mode. Nevertheless, register B2 can be accessed for reads and writes by addressing
EMIOSB.
Output Pulse Width Modulation Buffered (OPWMB) Mode
OPWMB mode (MODE[0:6] = 11000b0) is used to generate pulses with
programmable leading and trailing edge placement. An external counter driven in MCB Up
mode must be selected from one of the counter buses. A1 register value defines the first
edge and B1 the second edge. The output signal polarity is defined by the EDPOL bit. If
EDPOL is zero, a negative edge occurs when A1 matches the selected counter bus and a
positive edge occurs when B1 matches the selected counter bus.
The A1 and B1 registers are double buffered and updated from A2 and B2,
respectively, at the cycle boundary. The load operation is similar to the OPWFMB mode.
FLAG can be generated at B1 matches, when MODE[5] is cleared, or in both A1 and
B1 matches, when MODE[5] is set. If subsequent matches occur on comparators A and B,
the PWM pulses continue to be generated, regardless of the state of the FLAG bit.
FORCMA and FORCMB bits allow the software to force the output flip-flop to the
level corresponding to a match on A1 or B1 respectively. FLAG bit is not set by the
FORCMA and FORCMB operations.
At OPWMB mode entry the output flip-flop is set to the value of the EDPOL bit in
the EMIOSC[n] register.
Some rules applicable to the OPWMB mode are:
•
B1 matches have precedence over A1 matches if they occur at the same time within
the same counter cycle.
•
A1 = 0 match from cycle n has precedence over B1 match from cycle n-1.
•
A1 matches are masked out if they occur after B1 match within the same cycle.
•
Any value written to A2 or B2 on cycle n is loaded to A1 and B1 registers at the
following cycle boundary (assuming OU[n] bit of EMIOSOUDIS register is not
asserted). Thus the new values will be used for A1 and B1 matches in cycle n+1.
eMIOS used in the Smart Car Race Project
For the Smart Car Race, we used the eMIOS with three different modes. Modulus Counter,
Output Pulse Width Modulation Buffered and Input Width Modulation Buffered. Basically, the
eMIOS is used to control three drivers of the car, the motors, the servomotor and the camera. The
“Table 2.1” shows how the eMIOS work in each driver:
Motor
ServoMotor
• Using the OPWM we control the power
consumed by the motors.
• With a OPWM signal with a small duty cycle, we
can control the position of the servomotor.
Functions of the EMIOS_Driver
To have a good idea of what’s happening in the driver, we just initialize and configure the
channels and the respective registers to generate each signal. The Table 2.2 shows how each
function works.
Function
How it works
1. vfn_initEMIOS_1(void);
Handling the MCR register to initialize the
EMIOS Modulus. Writes “15” in the bits
of GPRE to divide the clock by 16 (15+1)
what led us a clock of 4 MHz because we
are using the clock as 64MHz. In the same
way, we enable the eMIOS clock, the
global time base and the stopping
channels when is in debug mode.
2. vfn_initEMIOS_chOPWM(T_UBYTE
lub_EMIOS_ch,T_UWORD luw_busA, T_UWORD
luw_busB, T_UBYTE lub_counterBus);
The EMIOS channel is initialized writing in
the Control Register the mode as OPWM,
the counterBus and the polarity-leading
edge. In the argument of the function we
enable the EMIOS channel we want to
initialize, the value of the Register A and
B and the counter bus we want to use.
3. vfn_initEMIOS_modCnt(T_UBYTE lub_cntCh,
T_UWORD luw_period, T_UBYTE lub_prescaler);
The clock base is generated in this
function. To generate it, we have to
configure the counter modulus and
indicate the period of the clock. The
arguments of the function are the
counter channel and the period of the
clock.
4. vfn_initEMIOS_pad(T_UBYTE lub_pad);
Initialize the pad in the EMIOS function in
the PCR register of the System
Integration Unit Lite (SIU).
Variables and constants in the Driver
Function
Properties
Function: vfn_initEMIOS_chOPWM
1. lub_EMIOS_ch
Stores: The number of the EMIOS channel we want to
initialize and modify as a PWM.
Function: vfn_initEMIOS_chOPWM
2. luw_busA
Stores: The value of the register we want to change to
modify the duty Cycle of the signal PWM.
Function: vfn_initEMIOS_chOPWM
3. luw_busB
Stores: The value of the register B. In the mode PWM it’s
usually initialized with the same value of the period.
Function: vfn_initEMIOS_chOPWM
4. lub_counterBus
Stores: The value of the counter bus where the Modulus
Counter will place the signal generated. Bus A (0x0), bus
B,C,D,F (0x1) and internal bus (0x3).
Function: vfn_initEMIOS_modCnt
5. lub_cntCh
Stores: The value of the EMIOS channel used as a
Modulus Counter.
Function: vfn_initEMIOS_modCnt
6. luw_period
Stores: The period of the signal that we want to
generate with the modulus counter.
Ex: If we store (999 + 1) and we have a signal of 1MHz,
the Modulus Counter will generate a signal of 1KHz.
7. lub_prescaler
Function: vfn_initEMIOS_modCnt
Stores: The prescaler of the general clock. If the EMIOS
clock is 4MHz and if our prescaler variable is (3 + 1), at
the end our signal will be 1MHz.
Function: vfn_initEMIOS_pad
8. lub_pad
Stores: The number of the pad we want initialize with
the EMIOS function.
Sistem Integration Unit Lite (SIUL)
The System Integration Unit Lite (SIUL) controls the MCU pad configuration, ports, generalpurpose input and output (GPIO) signals and external interrupts with trigger event configuration.
The module provides the capability to configure, read, and write to the device’s general-purpose
I/O pads that can be configured as either inputs or outputs.
 When a pad is configured as an input, the state of the pad (logic high or low) is obtained by
reading an associated data input register.
 When a pad is configured as an output, the value driven onto the pad is determined by
writing to an associated data output register. Enabling the input buffers when a pad is
configured as an output allows the actual state of the pad to be read.
 To enable monitoring of an output pad value, the pad can be configured as both output
and input so the actual pad value can be read back and compared with the expected value.
Pad Configuration Registers (PCR0–PCR122)
The Pad Configuration Registers allow configuration of the static electrical and functional
characteristics associated with I/O pads. Each PCR controls the characteristics of a single pad.
Please note that input and output peripheral muxing are separate.
• For output pads:
— Select the appropriate alternate function in Pad Config Register (PCR)
— OBE is not required for functions other than GPIO
• For INPUT pads:
— Select the feature location from PSMI register
— Set the IBE bit in the appropriate PCR
• For normal GPIO (not alternate function):
— Configure PCR
— Read from GPDI or write to GPDO
Table 1.1- PCR description
Analog Pad Control (APC)
This bit enables the usage of the pad as analog input.
— 0: Analog input path from the pad is gated and cannot be used
— 1: Analog input path switch can be enabled by the ADC
Pad Output Assignment (PA [1:0])
This field is used to select the function that is allowed to drive the output of a multiplexed pad.
—
—
—
—
00: Alternative Mode 0 — GPIO
01: Alternative Mode 1 — See the signal description chapter
10: Alternative Mode 2 — See the signal description chapter
11: Alternative Mode 3 — See the signal description chapter
Output Buffer Enable (OBE)
This bit enables the output buffer of the pad in case the pad is in GPIO mode.
— 0: Output buffer of the pad is disabled when PA[1:0] = 00
— 1: Output buffer of the pad is enabled when PA[1:0] = 00
Input Buffer Enable (IBE)
This bit enables the input buffer of the pad.
— 0: Input buffer of the pad is disabled
— 1: Input buffer of the pad is enabled
GPIO Pad Data Output Registers
These registers are used to set or clear GPIO pads. Each pad data out bit can be controlled
separately with a byte access.
Pad Data Out
This bit stores the data to be driven out on the external GPIO pad controlled by this register.
— 0: Logic low value is driven on the corresponding GPIO pad when the pad is configured as
an output.
— 1: Logic high value is driven on the corresponding GPIO pad when the pad is configured as
an output.
GPIO Pad Data Input Registers
These registers are used to read the GPIO pad data with a byte access.
Pad Data In
This bit stores the value of the external GPIO pad associated with this register.
— 0: Value of the data in signal for the corresponding GPIO pad is logic low
— 1: Value of the data in signal for the corresponding GPIO pad is logic high
SIUL in the Smart Car Race
The System Integrate Unite Lite is used to configure pads with different functions, ADC,
EMIOS and GPDIO. In order to have organization in our code, each function is assigned in each
driver, depending the functionality of the pad is the driver that configures it.
Functions of the GPDIO_Driver
Function
How it works
1. vfn_initGPDIOout(T_UWORD
lub_gChannel);
Initialize the PCR of the channel
“lub_gChannel” as Output.
2. vfn_initGPDIOin(T_UBYTE
lub_gChannel);
Initialize the PCR of the channel
“lub_gChannel” as Input.
3. vfn_setGPDO(T_UWORD
lub_gChannel, T_UBYTE lub_gValue);
Sets the “lub_gValue” to the channel
“lub_gChannel”. The variable “lub_gValue” can
be just ‘0’ or ‘1’ because GPDO is just for one
bit.
Macros and Variables
Name
Register or Constant
1. luw_gChannel
Stores the number of the PCR register.
2. lub_gValue
Stores the value that is assigned to a pad.
HAL (Hardware Abstraction Layer)
Motors
One of the main parts of the system is the Motors. If we have a simple and easy way to
control the motors we will be able to introduce other complex controllers to the system. Our idea
is to convert the percentage of power consumption we want into the duty cycle of the PWM signal
that we are going to generate.
Power
Consumption
Duty Cycle of
the PWM signal
To generate the entire driver, we have to use the EMIOS driver to initialize the channels
and the pads that we are going to use with this functionality.
First we initialize the eMIOS, the counter modulus and the pad of the motors. This is just
one function. Then, we have another function to convert a value in the range of 0 and 100, which
is the power consumption, into the period we need to generate a signal with those characteristics.
Functions of the Motor Driver
Function
How it works
1. vfn_initMotors(void);
Initialize the eMIOS, the counter modulus with
a frecuency of 1000Hz and the pad used to
control the motors.
2. vfn_setDuty(T_UBYTE lub_dutyCycle);
Sets the duty Cycle of the PWM signal just
multiplying the variable “lub_dutyCycle” for 10
to get a value between 0 and 1000 which is the
value used as period in the bus A.
Macros and Variables
Name
Value or Register
1. cub_MotorEMIOSch
EMIOS channel used for the Motors.
Value = 6
2. cub_MotorPad
Number of the PCR of the emios channel 6.
Value = 116
3. cub_MotorCntCh
EMIOS channel used as a Modulus Counter.
Value = 23
4. cuw_MotorPeriod
Period wanted for the PWM 1ms - 1KHz.
Value = (999 + 1)
5. cuw_MotorBbus
Constant of the Bus B.
Value = (999 + 1)
6. cub_MotorCntBus
Define the Bus A as default.
Value = 0
7. cub_MotorPrescaler
In order to have a signal of 1MHz we have to
divide the max frequency by (3+1) = 4
8. lub_dutyCycle
Variable written in the argument of the
function to set the motor at “lub_dutyCycle”
power consumption.
9. luw_MotorAbus
Variable used to Convert dutyCycle to Period.
Sensors Driver
Functions
Functions
How it works
1. vfn_initSensors(void);
Initialize the ADC timing conversion, the pads
used as ADC channels and the mode of
operation of the ADC. It also initialize the pads
as general purpose (GPDO), used to multiplex
each sensor and avoid interference noise.
2. vfn_getSensors_Value(void);
Gets the Value of each sensor and puts the
value in an array, each sensor is multiplexed to
get one value at a time so we can save energy
and avoid noise.
Macros and Variables
Name
1. cub_FirstSensorPad
Value or Register
First pad of the multiplexer port. Used like a
base to know the first pad we are going to
multiplex.
Servomotor Driver
Functions
Function
How it works
1. vfn_initServo(void);
Initialize the eMIOS driver to generate the
signal of the Servo. The signal has a frequency
of 62.5Hz with a period of 0.016 seconds.
2. vfn_setServoPos(T_UBYTE
lub_ServoGrados);
With this function, we just have to assign the
degrees and the servo will spin in that position.
Macros and Variables
Name
Value or Register
1. cub_Servo_pad
Pad used for the Servo PH3.
Value = 115
2. cub_Servo_emiosCh
EMIIOS channel used for the Servo.
Value = 5
3. cub_Servo_Cntch
Number of the Modulus counter used for the
Servo. Value = 0
4. cuw_Servo_Period
Period of the Servo Signal. Value = (15999 + 1)
= 16000 (16ms) -> (62.5Hz)
5. cub_Servo_prescaler
Prescaler used to get a signal of 1MHz in the
Modulus Counter. Value = 3
6. cub_Servo_counterbus
Constant that assign the bus B to the PWM
Value = 0x1
7. cub_Servo_calibration
Calibration to have a straightforward direction
with 90° degrees. Value = 4
8. lub_ServoGrados
Stores the value of the degrees that we want to
set the servo.
9. lf_Servo_Aperiodo
Stores the value of the equation used to get
the period.
10. luw_SerPeriod
Stores the Period in an integer value.
APP (Application Layer)
PID Driver
Implementation
To know the position of the Line in the entire line of sensors we decide to weight each
sensor. In order to get two data in just one variable, we decide to weight the values of the sensors.
The magnitude of this weight values decides how much we have to spin the servomotor and the
sign of this variable decides the side of the spin.
N° of the
Sensor
Weight Value
1
2
3
4
5
6
7
8
9
10
11
|
(-5)
|
(-4)
|
(-3)
|
(-2)
|
(-1)
|
(0)
|
(1)
|
(2)
|
(3)
|
(4)
|
(5)
ADC Value
Voltage Value
Weight Value
Final Error
Process of the data in the PID
Implementation of the PID
One of the critical steps in the Control of the Car was how to get the error. The weight
values answered this question. The weight values give us the opportunity to know, with just one
variable, the position of the car in relation of the line. For example, let’s say that the car is a little
bit moved right of the line. If we know the answer of the black color, which is in the range of (2.3 3.5) and the answer of the white color, between (0.2 – 1.2), we can get the value of each side and
then add both parts. The left part will be weight with negative values and the right part of the
board with positives. So, in the example, the voltage of the sensor would be:
#Sensor 1
Value
0.2
2
0.2
3
0.2
4
0.2
5
0.2
6
0.2
7
2.3
8
2.3
9
0.2
10
0.2
11
0.2
10
0.2
(4)
0.8
11
0.2
(5)
1
The next step would be multiply the Values of the voltages and the weight values:
#Sensor
Value
Weight V.
Final
1
0.2
(-5)
-1
2
0.2
(-4)
-0.8
3
0.2
(-3)
-0.6
4
0.2
(-2)
-0.4
5
0.2
(-1)
-0.2
6
0.2
(0)
0
7
2.3
(1)
2.3
8
2.3
(2)
4.6
9
0.2
(3)
0.6
Then, we create a variable of each side:
Variable_Left_Side = (-1) + (-0.8) + (-0.6) + (-0.4) + (-0.2) = -3
Variable_Right_Side = (2.3) + (4.6) + (0.6) + (0.8) + (1) = 9.3
Error = Variable_Left_Side + Variable_Right_Side = (-3) + (9.3) = 6.3
As we can see, if the black line is shifted more in the right side, the error will be higher. It’s
the same if the line is in the left part but the error will be negative.
Then, the Integral and Derivative value are compute.
Integral_Value = Integral_Value + Error
Derivative_Value = Error – Last_Error
Once we have the three parts of the PID controller we have to eliminate the error spinning
the Servo and changing the velocity of the motors. After that, we are able to compute again the
error. This process is showed in the next flowchart.
Starts PID
Obtain the
value of
the sensors
The conversion
is converted
into voltage
Each voltage
of the sensors
is weighted
to get a better
error of the
system
Computes the error
Computes the integral
and derivative values
If the
error > MaxTurn
Yes
Assign the maximum
shift to the servo.
Sets the ServoMotor and
the Motors depending
of the error
PID flowchart
No
Compute the
shift in base of
the error
Functions
Function
How it works
1. vfn_initPID(void)
This function Initialize the driver of the Motors,
the Sensors and the Servomotor
2. vfn_setPIDposition(void)
First, the function compute the value of the
error.
Macros and Variables
Name
Value or Register
1. Kp
Constant of proportionality
2. Ki
Constant of integral
3. Kd
Constant of derivative
4. Km
Constant of proportionality of the motor
5. MaxVoltage
Maxim Voltage used to compute the real
Voltage value
6. Resolution
Resolution of the ADC (10 bits)
7. rsf_PIDerror
Probably, this variable is one of the most
important variables of the system because it
tells us how far or how much we have to spin
the servo to stabilize the car and be in the
middle of the line.
8. rsf_PIDneg
We add the left part of the sensors (the
negative one) to have a reference of the left
part of the sensors board.
9. rsf_PIDpos
We add the right part of the sensors (the
positive one) to have a reference of the right
part of the sensors board.
10. casw_PIDweightValues
Stores the constants of the weighted values
used to help the process to manage the data.
This array gives a specific weight to each
sensor, giving us more information about
where is the line.
11. raf_PIDvoltageweight
Stores the value of the voltage weighted. Once
we have the real value of the voltage, we
multiply each position of the weight values to
each position of the voltage values. The result
is saved here.
12. raf_PIDvoltage
Stores the value of the real Voltage measured
by the ADC
13. ruw_PIDTurn
Stores the conversion Error -> Turn to put it in
the Servo
14. rsf_PIDderivative
Stores the value of the derivative part of the
PID
15. rsf_PIDintegral
Stores the value of the integral part of the PID
16. rsf_PIDLastError
Store the memory of the last error used by the
derivative part
Scheduler
Configuration of the Scheduler
To be able to have a real Time response, we define only 2 tasks in the Scheduler. The
propose to have only 2 task is to divide the tasks in two groups. In the First group, we have two
features, this features get the feedback of our system. This feedback is obtained by the sensors
and then computed them by the PID feature.
Scheduler Table
Our other group is the response of our motors to stabilize the system. The first feature is
the servomotor, this feature reacts depending of the error signal, as higher is the error as higher is
the spin of the servo. In the same way, the Motors accelerate when the error is low and the
integral value is low. This ensures the stability of the car even if the sensors board is out of the
line.
Procedure of the Control Group
Procedures of the Response Group
Why we use the Scheduler?
According to our delay times in the Tasks, we assign 2 ms for the Control group and 4 ms
for the Response group. This means that the Control Group will be execute 2 times for each time
the Response Group is executed. But the question is why? The answer is the integral and
derivative values. If we execute the PID control a lot of times, our system will respond more
precisely. It is true that the Servo and the motors just see the proportional value of the same
process, but it is also true that they will see the integral and derivative values of both processes.
This is really helpfully because we will have a record of those values that need to be observed at
any time. The next Table shows how the Tasks are executed.
Tasks