Balancing Start-up and Stand

Balancing Start-up and Stand
Balancing Start-up and Stand-by Time
I
Functional View
Enable UI
1.1
On the readiness for operation of a digital camera
Start Camera
Start Display
Enable Buttons
Approximately 22% of all photos are taken with flash light.
1
2
The chance that a photo needs flash light given that a photo with flash light was taken in the last 15 minutes is 95%.
Stand-by Power
3
Metadata include time, orientation of the camera, GPS location, compass heading, and camera settings.
4
To prevent a state space explosion, we ignored the least relevant parts and combined some other parts.
5
Leakage causes a fully charged flash light to become discharge completely in two minutes. When a flash light is partially
charged, its Start-up Time is of course shorter than in case of a cold start-up.
6
Status include battery level, start-up progress (using hour-glass animation), available memory (in number of photos), and
digital camera settings.
7
Clearly observable start-up activities, like extending the lens and opening the lens cover, reduce the Subjective Start-up
Time.
8
A shutter-like lens cover was rejected since the Robustness of the design was less. In particular, the design is more
sensitive to dust and external forces.
9
A manual cover was rejected since the Start-up Time of the design is longer. Removing a manual cover requires
approximately 0.5 second. Furthermore, it is typically forgotten (approximately 70%): Instead of removing the cover in
parallel during digital camera start-up, it is removed after start-up.
10
Left-handed thread was rejected, although there are no difference in relevant system qualities between right-hand and
left-hand thread used to extend the lens.
11
A fixed lens was rejected since the design negatively impacts the digital camera’s Ease of Transportation and requires
more Digital Zoom than currently possible without compromising the Image Quality.
12
To ensure low Cost, a generic System On Chip solution has been chosen instead of dedicated, special-purpose
hardware.
13
The digital camera’s start-up and stand-by design must be simple to implement to ensure low Cost not only now but also
in the future.
20
14
Ease of Transportation is achieved by folding the lens, resulting in a convenient form factor. The folding of the lens is
under control of the user by pressing the on/off button.
15
15
The lens must be protected against dust and external forces to prevent damage and to ensure the Image Quality during
the camera’s complete Life Time.
16
For both Image Quality and Ease of Transportation, the light path is only enabled when sufficient power is available in
the batteries to prevent a partially opened cover [that leaves the lens unprotected], and a partially extended lens
[resulting in an inconvenient form factor].
17
The on/off button is always enabled. For Reliability, all other buttons are disabled to prevent erroneous input while the
camera is stored.
18
For both Image Quality and Reliability, image acquisition is only enabled when sufficient power is available in the
batteries among others to prevent damage to the sensor and permanent storage.
19
Dedicated GPS tracking hardware is chosen to enable a long Stand-by Time. A GPS software tracking application
consumes too much power in the warm state, since the satellites have to be continuously tracked, requiring all
dependent parts, including System on Chip, CPU and OS, to be in the hot state.
20
Currently, after initialization, the GPS hardware returns either “no-signal” or the GPS position. In the next release, the
software driver will be changed such that during GPS hardware initialization “no-signal” will be returned. This will reduce
the Start-up Time from 915 ms to 841 ms. Furthermore, a photo taken when no GPS signal was available will be tagged
with a GPS position (and its associated timestamp) when a GPS position was or becomes available within a 1 minute
time window around the time the photo was taken.
Stand-by Time ~
17
Preferred Solution
Enable Image Acquisition
Use UI
6
4.1
4.4
3.1
14
Alternatives
8
16
9
3.3
Illuminate Scene
15
3
3.2
Extend Lens
Remove Lens
Protection
4.3
Enable Light Path
Start Metadata
Collection
Start Sensor
4.2
Enable Permanent
Storage
Display Status
Start Signal
Processing
5.1
18
Preferred Solution
Alternatives
10
11
Camera FullFunctional
Start-up Dependencies
II
Design decisions / constraints
1
High-end rechargeable AA
battery: 1.2 V – 3000 mAh
Assumed stand-by power: 12 mW
Stand-by time / battery runs flat in:
3000 mAh / (12 mW/1.2V) = 300 h
= 12.5 day
Check Battery Level
2
IV
Of Digital Camera Parts
Fixed lens
1.1
Display Controller
Display
3.1
Pareto Frontiers
Lens Cover
Lens Controller
3.2
Lens Extender
2
25
3.3
Battery Controller
Flash Light
4.1
ISP
Image Sensor
4.2
OS
Application
Camera
SoC
4.2
GPU
12
4.2
RAM
Memory Controller
4.3
Flash Memory
Power (mW)
CPU
1
Flash 1
10
No Flash
2
4.4
Inertial Measure Unit
4.4
5
Compass
4.4
III
Quantification of Key Parameters
start-up: max
power: 0 mW
4
Digital Camera Part
1.1
2
3.1
3.2
3.3
4.1
4.2
4.3
4.4
0
GPS
Display Controller
Display
Battery Controller
Lens Controller
Lens Cover
7
Lens Extender
Flash Light 5
System On Chip
ISP
Image Sensor
CPU OS Application
GPU
RAM
Memory Controller
IMU + Compass
20
GPS
start-up: intermediate
power: intermediate
3
400
600
800
1000
1200
7
start-up: 0 ms
power: max
Cold
Warm
Hot
start-up start-up power power
(ms)
(ms) (mW) (mW)
78
15
0.3
2.3
213
35
3.4
6.2
12
0.1
69
21
0.3
1.7
312
248
1.8 15
14
697
482
2.6
1123
6.9
123
15
0.3
1.3
152
15
0.3
4.3
674
62
1.5
3.2
304
74
0.2
4.3
24
2.1
101
10
1.1
2.6
76
2
0.1
1.1
53
1.1
915
351
7.9 46.5
4
Start-up Time (ms)
Digital Camera Start-up and Stand-by Design
13
1
718 ms @
15.8 mW
2
1
Hot
Battery Controller, Flash Light
Warm
GPS, SoC, Lens Controller, ISP
Hot
Battery Controller
Warm
GPS, SoC, Lens Controller, ISP
Legend
Usage Profile
UI
25
3
5
Stop Camera
4 minutes
14
4
No user interaction
2
No
2 minutes
Battery Controller
Warm
SoC
minute
day
hour
20
Yes
Photo with
flash light in
last 15
minutes?
Hot
915 ms @
0.4 mW
3
20
2 hours
P(photo) < 1%
Hot
-
Warm
-
961 ms @
0 mW
4
Chance Next Picture (%)
19
Light Path
Image Acquisition
Function
15
Temporal Order
10
1
Function Identifier
1
Usage statistics
3
Clarification
7
Design Decision
5
1
5 minutes
2
P(photo) < 5%
718 ms @
8.9 mW
0
1
10
100
1000
Time (s)
10000
100000
1
Digital camera stand-by mode
Balancing Start-up and Stand-by Time
Definitions and Abbreviations
Cold
Hot
State in which part performs no activity: it consumes no power and needs maximal
time to start-up.
State in which part is fully active: it consumes maximal power and is ready for
operation.
Warm
State in which part has reduced activity: it consumes some power to enable a faster
start-up. E.g., processor runs with a reduced clock frequency, or OS is hibernated.
CPU
Central Processing Unit
OS
Operating System
GPS
Global Positioning System
RAM
Random Access Memory
GPU
Graphics Processing Unit
SoC
System on Chip
IMU
Inertial Measure Unit
UI
User Interface
ISP
Image Signal Processor
On the readiness for operation of a digital camera
Model Status: APPROVED (v4 Nov 2010)
Related System Concerns
Model ID: ESI 2.20.4.3.1
When dealing with the readiness for operation of a digital camera, many other system concerns have
to be taken into account as well. The relevant system concerns are visualized below. These concerns
result in the Key Parameters & Requirements as describe in the next section.
Reviewers: Pierre America, David Watts, Teade Punter
Non-Functional
Technology
Business
Price
Image Quality
Ease of
Transportation
Subjective
Start-up Time
Power
Consumption
Performance
Weight
Unintrusive
Stand-by Time
Digital Zoom
Life Time
Reliability
Robustness
· Since many events happen on the road, a digital camera should be easy to carry around
and robust against travelling conditions.
Response
Time
Zoom Lens
· To capture the moment a digital camera should be able to instantly take photos. Since a
digital camera can be turned off, it should have a short start-up time.
Time to
First Photo
Zoom
· A digital camera might not be used for weeks. Due to consumption of power in stand-by
mode, the battery can run flat and the digital camera is no longer ready to take photos. A
digital camera should thus not only have a long stand-by time but also clearly
communicate the battery level to the user to prevent unexpected flat batteries.
When taking a photo, the user of the digital camera might not want to interfere with the
current event. For example, a user might want to take photos of children playing without
distracting them from their current activities. For this purpose a high-quality zoom is needed.
2. Top-level Functional View
The digital camera contains four functional parts:
battery management, user interface (UI),
image acquisition, and light path.
The enabling of both the light path and image
acquisition is conditional on the outcome of the
battery level check. The elements in the light
path and for image acquisition are thus
protected against the battery running flat.
Enable UI
Use UI
Check Battery Level
Enable Image Acquisition
Enable Light Path
Camera FullThe enabling of the UI is executed in parallel
Functional
with the battery level check. The digital camera
thus always tries to start the UI independent of
the battery level. The UI also uses the output of the battery level check: When the battery
level is too low to start the digital camera an appropriate message, like please replace
battery, will be shown on the display.
The reader should consult the Functional View on the other side for additional details.
3. The States of a Digital Camera
A part of a digital camera can be in a cold state, i.e., no activity, or in a hot state, i.e., fully
active. Many parts of a digital camera can also be in a warm state, i.e., reduced activity. A
digital camera thus seems to have millions of states: the product of the states of all its parts.
A part can only be in a state, when all parts it (physically) depends on are in the same or
higher activity state. To give a few examples: software can not run when the OS is
hibernated, and a CPU can not be in reduced clock cycle mode when the enclosing System
on Chip is off. The dependencies of a digital camera are shown on the other side. These
dependencies reduce the millions of theoretical states of a digital camera to a few hundred
thousands valid states.
For the readiness for operation of a digital camera, only approximately ten states turned out
to be relevant, since they have unique start-up and stand-by power consumption
characteristics: A faster start-up can not be achieved without consuming more power, and
less power can not be consumed without increasing the start-up time. These relevant states
form a so called Pareto frontier [5] that is shown on the other side. Since illumination of the
scene is not always needed and a flash light has both a long start-up time and a high standby power consumption, two Pareto frontiers are drawn: with and without flash light.
The digital camera’s start-up and stand-by design must be simple to implement and change,
since technological advancements will change the quantification of key parameters and thus
the Pareto frontier. The final design uses only four states on the Pareto frontiers. The
transition between states is based on the usage profile of a digital camera, in particular, on
the chance of flash light usage and on the chance that the next picture will be taken, as
shown on the other side.
Design Strategies
· The digital camera gets power from a battery. The battery can run flat. A flat battery
should not leave the digital camera in an inappropriate state, such as a partially
covered lens that is sensitive to damage or a partially extended lens that makes the
digital camera difficult to handle and store. Therefore, the battery is checked during
start-up before initiating changes in state to ensure completion of those changes.
· When photos are taken in the dark illumination of the scene is needed. The digital
camera is equipped with a flash light for this purpose. However, charging a flash light
takes quite a lot of time, and a charged flash light leaks quite some power. In fact,
without power, a flash light complete discharges in approximately two minutes. Since a
flash light is not always needed, we have considered both cases: with and without
flash light. This resulted in a stand-by strategy of the digital camera that depends on
the usage of flash light in the last 15 minutes.
Key Parameters & Requirements
Roadmap
(Objective) Start-up Time: Time needed to enable full-functionality. The user wants to take a photo of
the current event even when the digital camera is turned off.
- Present:
Subjective Start-up Time: Start-up Time as experienced by the user. The user does not want to wait
unnecessarily. Progress bars and clearly observable start-up activities, like extending the lens and
opening the lens cover, reduce the Subjective Start-up Time.
Stand-by Time: Maximal time after which a digital camera that is left unattended can still take a
photo. The digital camera might be laying around for weeks, yet the user expects to pick it up and to
take a photo.
Start Camera
Commentators: Daniel Borches, Gerrit Muller, ESI Research Fellows
Customer
Battery Power
Users of a digital camera want to take high-quality photos of relevant events. The digital
camera should thus be ready for operation during those events. This readiness has different
aspects.
Name: Pierre van de Laar
Contact Details: [email protected]
(Objective)
Start-up Time
1. Introduction
Owner
Response Time: The time between pressing the shutter button and photo being taken.
Time to First Photo: The time needed to start-up the digital camera and to take one photo. Note that
by interweaving start-up and photo taking the Time to First Photo can be less than the sum of the
Start-up Time and the Response Time.
Battery Power: The more power a battery contains, the longer before the battery runs flat.
Power Consumption: The more power is consumed, the quicker the battery runs flat.
Digital Zoom: Changing the area shown in the photo by changing the reading out of the sensor and
the processing of the sensor data.
Zoom Lens: Changing the area shown in the photo by changing the light path.
Zoom: Changing the area shown in the photo.
Cost: Expenses needed to realize the digital camera, including Bill-of-Material and development and
manufacturing costs.
Performance: Behavior of the digital camera, ranging from Start-up Time to Ease of Transportation,
and from Stand-by Time to Response Time.
Life Time: Period of time during which the digital camera can be used.
Image Quality: The lens and sensor are key to achieve high-quality photos. Therefore, when the
digital camera is not used, the lens is always protected to prevent damage and thus to ensure high
quality photos throughout the digital camera’s Life Time. Furthermore, the sensor is only operated
when sufficient power is available in the battery to prevent any possible damage due to usage
outside specifications.
Ease of Transportation: The digital camera should be easy to carry and store, among others in a
pocket or bag.
Weight: The digital camera should not be too light (to reduce vibrations and improve Image Quality)
and not be too heavy (for Ease of Transportation). The battery’s weight constitutes approximately
40% of the digital camera’s weight.
Unintrusive: The user wants to take a photo without interfering and intruding in the scene. For this
reason a high-quality zoom of at least 15x is needed. Currently, this can only be realized using an
extendable zoom lens.
Reliability: Photos stored in the permanent storage can only be removed explicitly by the user.
Photos should never get lost or damaged. Therefore, buttons are disabled when the digital camera is
stored and the permanent storage is only accessed when sufficient power is available in the battery
to prevent any possible damage due to usage outside specifications.
Robustness: The digital camera should be able to withstand travelling conditions, including dust,
external forces, and extremes of weather conditions.
A digital camera has multiple modes to ensure the desired overall readiness for
operation. These modes handle the balance between start-up and stand-by time
differently based on the current usage.
- Past:
Image acquisition using film barely used power. Power was only consumed to open the
shutter to illuminate the film, to charge the flash light, and to display information in the
viewer. As a consequence, customers are used to cameras with long stand-by time.
- Future:
Improvements in LEDs will make them suitable to illuminate the scene. Whether LEDs
will replace or complement the flash light is not yet clear. Since flash light is dominant in
the balance between start-up and stand-by time, a change in illuminating the scene will
certainly cause changes in this architectural overview.
Improvements in image sensor and digital zoom will make high-quality digital zooming
possible. These improvements enable a digital camera with a fixed instead of an
extendable zoom lens. Without the extension of the lens, the start-up becomes less
observable by the user. This change will thus negatively influence the subjective start-up
time, making start-up time even more critical.
References
- Experts: Daniel Borches ([email protected]),
Gerrit Muller ([email protected])
- Documents:
[1] A3 Architecture Overview Cookbook – Daniel Borches
[2] ESI 2.20 System Architecting Course
- Other documents:
[3] Understanding A3 Thinking – A Critical Component
of Toyota’s PDCA Management System –
D.K. Sobek II and A. Smalley
[4] http://a3thinking.com/
[5] Pareto efficiency, http://en.wikipedia.org/wiki/Pareto_efficiency
- Relation with other design principles:
Power from the battery is also consumed during normal operations.
- Relation with other models:
The model uses the parts as described in the “Realization of digital camera” model.
- Model hierarchy:
Child of “Times & Digital Cameras”
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