ECNG3006 MICROPROCESSOR
APPLICATIONSCourse Instructor: Mr. Kevon AndrewsOffice: Rm. 239Phone: 1-868-662-2002 ext.3156Email address: [email protected] Hours: Mon: 2-3pm, Tue: 2-3pm, Fri:10-
12pm
COURSE OUTLINE
• Differences between PIC18F452 and PIC16F877• Processes• RTOS design• FreeRTOS Overview• FreeRTOS ISR• Example RTOS application & design issues• Real-time system• Scheduling Theory• Scheduling Approaches and Performance Issues
Unit Objectives
Recall differences between PIC18F452 and PIC16F877.
Apply knowledge of states of processes in applications examples.
Design real-time system application using the FreeRTOS implementation.
Outline the design of an RTOS.Analyse design issues of real-time systems using
FreeRTOS..
Unit Objectives (cont’d)
Reconstruct real-time systems using knowledge of design issues.
Define and classify different classifications of real-time systems according to their timing attributes.
Give examples of real-time systems as related to classification of real-time systems.
Explain concepts within scheduling theory.Describe scheduling algorithms.Analyse some issues and performance of schedules.
ASSESSMENT
• End of semester examination [50%]
• 50% Coursework [50%]
– Laboratory exercises [30% ]•Laboratory exercise 1 – Introduction to MPLAB
and C18 compiler [10%]
•Laboratory exercise 2 – C18 compiler and LCD [10%]
•Laboratory exercise 3 – FreeRTOS and LCD [10%]
–Mini-project [20% ]
Differences between PIC18F452 and PIC16F877
• Show general differences.
• Architectural differences.
• Changes in registers used for direct addressing and indirect addressing.
• Interrupt priority levels.
General Differences
16F877• 8192 prg instructions• 368 bytes RAM• 3 timers• 5 A/D channels• 14 interrupt sources• 35 instructions• private stack• 1-level interrupt
priority
18F452• 16384 prg instructions• 1536 bytes RAM• 4 timers• 8 A/D channels• 18 interrupt sources• 75 instructions• user addressable stack• 2-level interrupt
priority
Program Memory Map and Stack16F877 18F542
Architectural Differences
• The PC contains 21 bits, which means that it is capable of addressing 2MB memory.
• Only 32K of memory is actually on-chip, so a read outside of the physical memory will return 0's (NOP).
• There is now a separate Bank Select Register (BSR) instead of two bits in the Status register, but only the lower 4 bits are used.
Direct Addressing
• The BSR is used to switch the banks and can be loaded directly via the MOVLB instruction.
• We need 12 bits to address all the possible data memory locations, i.e. there are 4096 possible memory locations.
Direct Addressing
Indirect Addressing
• The indirect addressing mode using the FSR and INDF registers of the 16Fxxx has been retained except that there are now three sets,– INDF0, INDF1, INDF2– FSR0 (FSR0H, FSR0L)– FSR1 (FSR1H, FSR1L)– FSR2 (FSR2H, FSR2L)
• Why are there H and L versions of the FSR?
Indirect Addressing
Indirect Addressing
• There is a special instruction LFSR to load the FSR registers.
• As usual access to the INDFn registers actually references the memory location referred to by the FSRn register.
• In addition to the INDFn registers, there are an additional four registers associated with each of INDF0..INDF2.
Indirect Addressing
• All the indirect registers are– INDFn – no change after indirect access– POSTDECn – auto-decrement after
indirect access– POSTINCn – auto-increment after
indirect access– PREINCn – auto-increment before
indirect access– PLUSWn – use value in W as offset to
FSR, don't change either W or FSR
Interrupt Priority
• Each interrupt source, except INT0, has three bits to control its operation. The functions of these bits are:– Flag bit to indicate that an interrupt event
has occurred– Enable bit that allows program execution to
branch to the interrupt vector address when the flag bit is set
– Priority bit to select high priority or low priority
Interrupt Priority
• The interrupt priority feature is enabled by setting the IPEN bit (RCON<7>).
• When interrupt priority is enabled, there are two bits which enable interrupts globally. – Setting the GIEH bit (INTCON<7>) enables
all interrupts that have the priority bit set.– Setting the GIEL bit (INTCON<6>) enables
all interrupts that have the priority bit cleared.
Interrupt Priority
• When the interrupt flag, enable bit and appropriate global interrupt enable bit are set, the interrupt will vector immediately to address 000008h or 000018h, depending on the priority level.
• Individual interrupts can be disabled through their corresponding enable bits.
C differences
Pentium• char – 8 bits• int – 32 bits• short – 16 bits• long – 32 bits• float – 32 bits• double – 64 bits
18 series• char – 8 bits• int – 16 bits• short – 16 bits• long – 32 bits• float - 32 bits• double – 64 bits
Summary
• Differences between PIC18F452 and 18F877.• Differences in PC(21 bits vs. 13bits) and selection
of banks(BSR<3:0> vs 2 bits in Status Register).• Registers used in direct(BSR<3:0> & 8-bit
opcode) and indirect addressing(FSRn & INDFn / POSTDECn / POSTINCn / PREINCn / PLUSWn.
• Introduction of different priority levels.
Processes
• Define a process
• Describe the states of a process
• Define a context and context switch
Process
• Suppose instead of doing only one thing we have the computer do several jobs at the same time. These jobs are kept in memory and the CPU time is shared between them.
• Each job is called a process.• Each process behaves as if the CPU
belonged to it alone.
Processes
States of Process
Processes
• When a process moves from the running to either the waiting or ready state, it does not have access to the CPU as it has given it to another process.
• If it is to gain access to the CPU again, we must store all what it was doing so that we can restore it as if it never stopped!
• That information that we must store is called the context of the process.
Context
• A context is literally everything about the process, some things are– Program Counter– State of the stack– CPU registers– I/O state– Process state– ... etc
Context Switch
• When the CPU switches to another process, the old context must be saved and the new context loaded for the new process.
• This save/load is called a context switch.
SUMMARY
• Process is a job, which the CPU seems to execute at the same time.
• 5 states which can describe the status of a process: new; ready; waiting; running and terminated.
• Context includes everything about a process.
• Context switch is the saving of the old context and loading of the new context.
