Course Introduction

Hardware Software CoDesign

September 2011
Agenda
Course Introduction

1. Basic Themes that came out through the Historical Background

2. Basic Pitfalls – what to guard against

3. Problem Statement of a touch screen system

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Course Introduction
Basic Themes

1. Modeling :: Because parallelism is important, the choice of an appropriate modeling

paradigm is also important. Different modeling formalisms need to be developed that
capture the various aspects of system behavior.

2. Analysis and Estimation :: Different models of the same system behavior need to
be analyzed and estimated for performance. Performance would include tradeoffs for
Area, Speed, Power. Cost to build, Time to Market are other factors.

3. System-level partitioning, synthesis and interfacing :: The basic steps of co-

synthesis. A range of methodologies are applied for this.

4. Implementation generation :: Once the architecture has been generated and trade-
offs known, the designs for the hardware and software components must be created.

5. Co-simulation and Emulation :: This helps designers to evaluate architectures and

validate assumptions on implementations. Emulation uses FPGA / other emulation
techniques to further speed up execution of system models.

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Course Introduction
Basic Pitfalls – What to guard against

1. Transient Overloads :: Transient Overloads on multiple aspects like power, memory,

out of bandwidth, data loss, missed deadlines of critical tasks.

2. Analysis Paralysis :: Since there are many ways of doing it, there could be too many
factors which do not allow the system designer to take decisions. A few ways of
taking ”judgement” decisions are based on fixing a set of topmost criteria and then
working backwards.

3. Simulation & Complexity :: Simulation based performance verification, has a con-

ceptual disadvantage that it becomes disabling as complexity increases. There is a
great lot of dependence on the pattern provided for finding corner cases.

4. Applications of the SoC :: Generally an SoC would be implemented with a certain

fixed application in focus. In some cases, the SoC could be used in non-typical or
non-designed for applications. This would break some concurrency conditions which
were not forseen earlier. Basically, for each new application, one needs to re-run the
scenarios in case of using an existing SoC.

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Course Introduction

Problem Statement of a touch screen system

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Course Introduction

Problem Statement of a touch screen system – Requirements

1. Level 0 :: It should work at lowest cost.

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Course Introduction
Problem Statement of a touch screen system – Requirements

1. Level 0 :: It should work at lowest cost.

2. Level 1 :: Some more details :-

(a) System should continuously monitor for a touch.
(b) When screen is touched, find out the X and Y coordinates.
(c) Based on the event(s) of touch and location / pattern, tasks must be performed
/ activated.

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Course Introduction
Problem Statement of a touch screen system – Requirements

1. Level 0 :: It should work at lowest cost.

2. Level 1 :: Some more details :-

(a) System should continuously monitor for a touch.
(b) When screen is touched, find out the X and Y coordinates.
(c) Based on the event(s) of touch and location / pattern, tasks must be performed
/ activated.

3. Level 2 :: Some more details :-

(a) Automated Screen Calibration
(b) Automatically wakes up and goes back to standby to save power
(c) Simple to write software and drivers
(d) Programmable conversion rate

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Course Introduction
Problem Statement of a touch screen system – Requirements

1. Level 0 :: What are the basic components required

(a) An ADC which can do a ”voltage sensing”
(b) A uP which can take in the Digital Input from ADC and do processing.
(c) Some memory to store successive touch(s) and do a pattern recognition !
(d) A ROM memory to store program, calibration related data.

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Course Introduction
Problem Statement of a touch screen system – Requirements

1. Level 0 :: What are the basic components required

(a) An ADC which can do a ”voltage sensing”
i. What should be the accuracy, precision of the ADC? 8b, 12b
ii. Should the ADC be a differential mode or single ended mode.
iii. What should be the minimum acceptable frequency for the ADC? Depends on
how ”Human Machine Interface” like touch screen works.
iv. KBD controller does key debounce at 10 1̃5ms. Should this be a programmable
frequency. In what steps should it be programmable. What complexity will
be added to the system. Can we make the system more simple. What is the
tradeoff.
(b) A uP which can take in the Digital Input from ADC and do processing.
(c) Some memory to store successive touch(s) and do a pattern recognition !
(d) A ROM memory to store program, calibration related data.

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Course Introduction
Problem Statement of a touch screen system – Requirements
1. Level 0 :: What are the basic components required
(a) An ADC which can do a ”voltage sensing”
(b) A uP which can take in the Digital Input from ADC and do processing.
i. Write a small flow chart on how the data and control would flow from ADC to
uP and control the events based on touch.

ii. Write the software as if it was processor agnostic.

iii. What is the complexity of the program.
iv. Is an 8bit general purpose processor ok. What will require an upgrade to 16bit
or 32bit general purpose processor.
v. Is there anything in the program which can be hardware accelerated at low cost.
Will a DSP suffice for this application.
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(c) Some memory to store successive touch(s) and do a pattern recognition !
(d) A ROM memory to store program, calibration related data.
Course Introduction
Problem Statement of a touch screen system – Design

1. Level 1 :: What are the basic components which we can fix (pin down)
(a) The technology node based on requirements
(b) The ADC
(c) The uP or DSP

2. Level 2 :: Can we prototype this system using off the shelf components
(a) Create the IP required to interface ADC with the uP/DSP busses. Add any
hardware acceleration required.

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Course Introduction
Problem Statement of a touch screen system – Design Block Diagram

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Course Introduction
Problem Statement of a touch screen system – Software Design At the top
level, the software provides for the following :-

1. Configure the controller hardware.

2. Determine if the screen is touched.

3. Acquire Stable, debounced position measurements.

4. Calibrate the touch screen.

5. Send changes in touch status and position to the higher level graphics software.

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Course Introduction
Problem Statement of a touch screen system – Software Design
Configure the controller hardware.

1. Create a function named TouchConfigureHardware()

2. Decide – Should the driver be interrupt driven or polling driven.

3. In case of interrupts, the driver would actually use two :-

(a) An interrupt to wake up when the screen is initially touched, known as the PEN DOWN
interrupt.
(b) A second interrupt to signal when the ADC is available with the set of data
conversions (X, Y).

Determine if the screen is touched.

1. Create a function named WaitForTouchState ()

2. When the controller is in the detection mode and a touch is detected, an internal
interrupt can be generated called PEN DOWN IRQ.

3. This detection is based on Y-axis touch plane tied high, X-axis touch plane tied low,
and on the basis of touch the planes are shorted together and Y-axis plane is pulled
low.

4. The driver task would not consume any CPU time until the PEN DOWN IRQ event occurs.
It would wake up and go into conversion mode only once the user touches screen.

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Course Introduction
Problem Statement of a touch screen system – Software Design
Acquire Stable, debounced position measurements – Reading touch data

1. Create a function named TouchScan(). The outline of the procedure would be :-

(a) Check to see if the screen is touched.
(b) Take several raw readings on each axis for later filtering.
(c) Check to see if the screen is still touched.
(d) (Depending on H/W) store the readings to a memory block, or use FIFO entries.
(e) (Depending on H/W) if the ADC output is 12bit, either pack data into 16bit
(aligned) locations or chop/dither them to 8bit.
(f) Taking Stable readings (filtering by using oversampling) is necessary for higher
level drivers to act appropriately. NOTE :: This filtering could be a h/w function
if CPU bandwidth is critical factor.

Calibrate the touch screen.

1. In an ideal scenario, the calibration would be run once during initial product power up
and reference values saved in ”non-volatile” memory.

2. Create a function name CalibrateTouchScreen () in case the user wants to calibrate

using a graphical target on screen.

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Problem Statement of a touch screen system – Software Design

Send changes in touch status and position to the higher level graphics software.

1. Create a function named GetScaledTouchPosition(). This is a routine to read raw

values and convert them to screen co-ordinates.

2. Create a function named TouchTask (). This routine calls the actual task the user
intended to be run while using the touch screen.

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Course Introduction

Acknowledgements

1. Datasheet of IDT MK712 Touch Screen Controller

2. Application Bulletin ”Burr Brown” now TI (public domain information)

:: Touch Screen Controller Tips.

3. http://www.eetimes.com/design/embedded/4006455/Writing-drivers-for
common-touch-screen-interface-hardware

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