15-01-2013, 01:08 PM
Embedded Microcontroller Systems
[attachment=46961]
Performance Metrics
Latency – time delay between when I/O device is ready for service and when uC responds.
input device – time between when data is ready and when it is actually latched into uC
output device – time between when device is ready for new data and when it is sent.
Priority – determines the order of service when more than two or more devices request at the same time.
determines if a high-priority device can suspend a low-priority request that is currently being processed.
may want to implement equal priority so that no device monopolizes the uC.
Synchronization Methods
I/O devices can be in one of 3 “states”
idle – disabled or inactive, no I/O occurs
busy – working on generating an input (input I/O) or accepting an output (output I/O)
done – ready for a new transaction.
Busy to done transitions cause status flags to become true.
Buffering – FIFO Queue
Data is received (Get) in the same order that it was transmitted (Put)
As long as FIFO is not full or empty, both producer and consumer operate at their own rate.
Need a way for producer and consumer to know if FIFO is full or empty.
Synchronization – Periodic Polling
Periodic polling – uses a clock/timer interrupt to periodically check the I/O status.
Used in cases where interrupts are desirable (there is much to do in the main program) but the I/O device does not support interrupts.
Keypad is an example – will investigate in the next exercise.
Example – DC Motor
Important in LOTS of applications
cameras, drives, elevators, trains, robots…
Many types, but all work similarly:
Apply voltage across + and – leads, electrical energy is converted to mechanical energy.
For some range of voltage, the torque of the motor shaft is proportional to value of voltage.
Some Terminology
Control variables – properties we want to control (position, velocity, temperature, etc)
Control commands – output to actuators
Driving forces – the actuator forces that cause the control variables to change (heat, force, etc)
Physical plant – the thing being controlled
Incremental Control
Rate of sampling is very important
If sampling rate is too fast, actuators are saturated and a bang-bang system results.
If sampling rate is too slow, then controller will not keep up with plant.
Rule of thumb for rate: control execution rate is 10x the step response of the plant.
Must check for underflow and overflow after increment or decrement.
[attachment=46961]
Performance Metrics
Latency – time delay between when I/O device is ready for service and when uC responds.
input device – time between when data is ready and when it is actually latched into uC
output device – time between when device is ready for new data and when it is sent.
Priority – determines the order of service when more than two or more devices request at the same time.
determines if a high-priority device can suspend a low-priority request that is currently being processed.
may want to implement equal priority so that no device monopolizes the uC.
Synchronization Methods
I/O devices can be in one of 3 “states”
idle – disabled or inactive, no I/O occurs
busy – working on generating an input (input I/O) or accepting an output (output I/O)
done – ready for a new transaction.
Busy to done transitions cause status flags to become true.
Buffering – FIFO Queue
Data is received (Get) in the same order that it was transmitted (Put)
As long as FIFO is not full or empty, both producer and consumer operate at their own rate.
Need a way for producer and consumer to know if FIFO is full or empty.
Synchronization – Periodic Polling
Periodic polling – uses a clock/timer interrupt to periodically check the I/O status.
Used in cases where interrupts are desirable (there is much to do in the main program) but the I/O device does not support interrupts.
Keypad is an example – will investigate in the next exercise.
Example – DC Motor
Important in LOTS of applications
cameras, drives, elevators, trains, robots…
Many types, but all work similarly:
Apply voltage across + and – leads, electrical energy is converted to mechanical energy.
For some range of voltage, the torque of the motor shaft is proportional to value of voltage.
Some Terminology
Control variables – properties we want to control (position, velocity, temperature, etc)
Control commands – output to actuators
Driving forces – the actuator forces that cause the control variables to change (heat, force, etc)
Physical plant – the thing being controlled
Incremental Control
Rate of sampling is very important
If sampling rate is too fast, actuators are saturated and a bang-bang system results.
If sampling rate is too slow, then controller will not keep up with plant.
Rule of thumb for rate: control execution rate is 10x the step response of the plant.
Must check for underflow and overflow after increment or decrement.