PalmOS
Device
Processor
Speeds
|
P |
almOS 4·x (and lower)
devices use derivatives of the Motorola / Freescale Dragonball processor,
clocked at a variety of speeds from 16 MHz up to 66 MHz. The Dragonball, or MC68328, is based on the
68000 processor core, which powered the Amiga 500 and
Faster is Better?
For these types of device and the
majority of users, it’s important to establish that raw computing power is
simply not required. PalmOS is a
resource-efficient operating system, at least compared with the Microsoft
offerings of Windows on a desktop or PDA platform. Comparing the 66 MHz Super VZ processor with
the 16 MHz or 20 MHz devices, yes, the Super VZ is quicker – but most of the
difference is down to the screen refresh rates.
The user isn’t exactly kept waiting for most applications. When using Graffiti with the ROM
applications, the Palm IIIxe
can keep up even when underclocked to 10 MHz and all CPU optimisations switched
off.
What is of more relevance is how
quickly the device can keep the screen up to date.
Wait States
The Dragonball EZ uses “wait states”
when accessing memory. This,
essentially, means that the processor hangs around for a little bit before it
continues to access memory. By removing
the wait states, you can accelerate the performance by a significant amount -
ten to twenty percent. The later
Dragonball VZ doesn’t appear to use wait states, so running something like
Cruise Control, or using the relevant Afterburner settings, appears to make no difference to
processor performance.
Clock Speed
In simplistic terms, the clock
speed of a given processor family determines the speed of the chip. Although ultimately, the operating speed of
the device is determined by other factors (including the speed of memory
access and the screen speed), processor performance has a major impact on
the overall running speed of the device.
By changing the clock speed of the
device, you change the speed at which the processor handles data. Increasing the clock speed will accelerate
the chip, whereas reducing the clock speed will reduce the performance.
Taking the Palm IIIxe as an example, which is
clocked at 16 MHz at the factory, increasing the clock speed from 16 MHz to 20
Mhz will produce a theoretical processor performance increase of 25%, in other
words, at the new clock speed the processor’s performance should be 125% of the
original speed.
Similarly, reducing the clock
speed from 16 MHz to 13 MHz should reduce the processor’s speed down to 81¼% of
the original speed.
It is also true that both the
power consumption and the heat produced by the processor is determined by the
clock speed. The higher the clock speed,
the greater the power consumption and the heat output from the processor.
It is important to consider that
although the power consumption of the processor follows a broadly linear
relationship with the clock speed, the power consumption of the overall device
will follow a different rule. If the
clock speed is set to be too low, the processor will be working hard for a long
with the user being unable to do anything - thus the screen will be switched on
for a longer period than necessary. This
is especially significant where the device relies on a backlight, and you are
performing a processor-intensive operation!
The Results
It’s important for me to establish
that every PDA is more or less unique, and if you’re attempting to obtain the
following benchmarks with what appear to be identical devices, you may or may
not get quite the same results.
Palm IIIxe – Clock Speed
Comparison
This table illustrates the
relative performance of the Palm
IIIxe’s Dragonball EZ processor – with all other optimisations activated –
with clock speeds between 10 MHz and 24 MHz.
|
Clock
Speed (MHz) |
10 |
13 |
16 |
20 |
24 |
|
BenchMark 2·0 |
88% |
113% |
145% |
178% |
220% |
|
Speedy 2·0 |
61% |
77% |
99% |
121% |
149% |
|
yCPU scrn_write |
645 Kbs-1 |
879 Kbs-1 |
1126 Kbs-1 |
1379 Kbs-1 |
1702 Kbs-1 |
Click here to see the Benchmark 2·0 scores illustrated on a
graph.
Palm IIIc – Device Optimisation
This table below illustrates the
impact of processor and memory acceleration on the Palm IIIc. In order
to optimise the device, we remove all wait states and use the Fast MPx and Fast
Page modes in Afterburner.
|
Device |
IIIc Standard |
IIIc Optimised |
Accel- eration |
|
BenchMark 2·0 |
127% |
188% |
48% |
|
Speedy 2·0 |
105% |
119% |
13·3% |
|
yCPU scrn_write |
898 Kbs-1 |
1000 Kbs-1 |
11·4% |
As you can see, three different
benchmarking applications report different levels of overall system
acceleration, and the tangible acceleration is almost certainly somewhere between
11·4% and 48·0% - it’s enough to notice that the unit is a bit quicker, but not
by much. From my experience with my
Dragonball EZ devices, this fits in – you do notice a tangible performance
improvement, but it’s not especially significant. However, as “something for nothing,” it’s
worth doing.
One point to make is that the IIIc’s
screen write speed is sluggish as standard – just under 900 Kbs. That’s only marginally quicker than the optimised
IIIxe underclocked to 13 MHz. This
explains why the IIIc feels sluggish in use: the user is waiting for the screen
to redraw.
Overall Device Comparison
|
Device |
IIIxe
Optimised |
IIIc
Optimised |
m515 Standard |
Visor Pro Standard |
m130 Standard |
SJ33 Standard |
|
Benchmk 2·0 |
145% |
188% |
156% |
160% |
156% |
273% |
|
yCPU scrn_write |
1126 Kbs-1 |
1000 Kbs-1 |
3710 Kbs-1 |
1568 Kbs-1 |
1815 Kbs-1 |
30117 Kbs |
|
yCPU ManBrot32 |
21·89 s |
17·09 s |
12·78 s |
15·31 s |
13·5 s |
7∙94 s |
The Benefits Of A Quicker
Processor
I’ve thought long and hard about
this and I’ve reached the conclusion that whilst there is a certain advantage to
having a quicker processor under the hood of the PalmOS device, but in the
majority of cases it shouldn’t be a deciding factor in buying one. It’s the opposite with a Windows Mobile
device: you really do want that 500 MHz processor!
The Palm IIIxe is a good example of a relatively slow
device. With the help of memory and CPU
optimisation, it’s quick enough to deliver good enough performance for almost
all applications. By this, I mean that
I’m not noticeably kept waiting for the device.
The exceptions are when handling with large spreadsheets or word
processor documents using QuickOffice.
Some scrolling activities can be a little bit slow, but not too bad.
The Palm IIIc has an ostensibly quicker processor, but the
effect is often negated by a slower screen.
In most circumstances, there’s very little between the two devices, the
exception being the noticeably quicker recalculation of spreadsheet files, but the
slower screen redraw in certain games.
But the slower screen redraw is only noticeable if you’ve used other
PalmOS devices...
The Palm m515 has a dedicated display chip and this shows in
the dramatically quicker Screen Write figures.
It’s 3·7 times quicker than the Palm IIIc, and this means that you very,
very rarely have to wait for the screen.
So although the processor is quoted as being slower than the IIIc, in
the real world the device feels a lot snappier.
The Sony Clié SJ33 is benchmarked
at the fastest DragonBall PalmOS device.
It blazes through the benchmarks above, being nearly twice as quick as
the 33 MHz DragonBall VZ powered devices – just as you’d expect from a 66 MHz
DragonBall Super VZ powered device. However,
where the SJ33 really shines is in its screen performance. Over 30,000 Kbs compared with the m515’s 3,700
Kbs!
The Benchmarking Applications
Benchmark 2·0
© Neal Bridges, results taken from
2·0 (d’oh!), where a score of 100% is that of the Palm IIIxe.
Speedy
©Laurent Duveau, http://www.aldweb.com/, results taken
from v3·1, where a score of 100% is that of the Palm Vx.
YCPU
©2002 RH Nicholson, all tests were
computed using version 0·8i.