1. ©Alex Doboli Chapter 3: Hardware and Software Subsystems of Mixed-Signal Architectures (Part II) Alex Doboli, Ph.D. Department of Electrical and Computer Engineering State University of New York at Stony Brook Email:adoboli@ece.sunysb.edu

2. ©Alex Doboli Tachometer ISR Tachometer ISR used in PSoC Express Specification: –Fan speed is measured through 3 pulses produced by the fan –Time distance between consecutive pulses is used to find RPMs –Response to fan inputs: Decouple fan from PWM and drive at full speed Let fan speed stabilize Measure time between consecutive pulses Reconnect fan to PWM –The 3 pulses must be received within 3 sec, otherwise this represents an abnormal functioning that is handled by the ISR –Consecutive fan speed readings should be separated by at least 4 sec (otherwise readings are incorrect) –ISR should handle multiple fans

3. ©Alex Doboli Functionality is even-driven & corresponds to FSM Events are the tachometer pulses FSM states implement the controller response Interrupt-based solution vs. polling Reduced overhead (Estimate the overhead) How are interrupts generated? Tachometer pulses are not interrupts Real-time constraints 3 pulses within 3 sec (HW vs. SW solution) Two consecutive readings separated by at least 4 sec (HW vs. SW solution) Data structure for handling multiple fans State information tables Tachometer ISR

4. ©Alex Doboli Tachometer interfacing

5. ©Alex Doboli Specification of the tachometer ISR Introduces delay of 4 sec abnormal switch to next 4 sec delay

6. ©Alex Doboli Pseudocode for FSM1 ISR

7. ©Alex Doboli Pseudocode for FSM2 ISR

8. ©Alex Doboli Multiple tachometers

9. ©Alex Doboli Data structures for handling multiple tachometers

10. ©Alex Doboli Tachometer ISR implementation

11. ©Alex Doboli Specification: –Event-driven, FSM –Two FSMs used: one for the ISR functionality and one implements the timing requirement for the functionality Interrupt driven implementation –Reduces CPU idle times (overhead) –Interrupts are generated by programmable digital block (DCB02) Data structure (table) for multiple tachometers (fans) –Sharing of design for multiple tachometers Hardware & software implementation –FSM in software –Interrupt generation & time measurement in hardware –Maximum time constraint in hardware (block DCB03) ISR implementation

12. ©Alex Doboli Programmable General I/O Ports (GIOPs): –I or O ports –Connected to CPU, digital resources, programmable analog blocks –Driving capabilities –Can originate interrupt signals Pin block –Pin (chip package), input buffer, 1-bit register, output drivers, configuration logic 8 driving modes: –Resistive pull down, strong drive, high impedance drive, resistive pull up, open drain-drives high, slow strong, high impedance, open drain-drives low Global I/O ports

13. ©Alex Doboli Port driving modes (output)

14. ©Alex Doboli Driving mode is programmed through the registers PRTxDM2, PRTxDM1, and PRTxDM0 PRT0DMx is for port 0, PRT1DMx is for port 1, etc. Driving mode programming Driving modeDM2DM1DM0 Resistive pull down000 Strong drive001 High impedance010 Resistive pull up011 Open drain high100 Slow strong drive101 High impedance analog 110 Open drain low111

15. ©Alex Doboli GPIO block structure analog On, except analog To CPU To DBB/ DCB To I2C 1 from CPU from DBB/ DCB High impedance To interrupt logic

16. ©Alex Doboli GPIO programming 1.Data communication through register PRTxDR 2.Register PRTxGS (BYP bit) 3.Register PRTxIC (GPIO interrupt configuration)