Image Processing Reference
In-Depth Information
Figure 12 shows supply-noise maps obtained using these VMONs. Generally, although seven
measurement points is insufficient for rendering in a 3D surface expression, this simple
expression helps to understand the voltage relation between these points. This scheme
can also produce a supply-noise-map animation, and Figs. 12(a) to (f) show snapshots of
supply-noise maps corresponding to the timing points indicated in Fig. 11. Figure 12(a) is
a snapshot when the CPUs are not operating but are consuming clock power. The location
of each VMON is shown in Fig. 12(a). Note that the APL-RT CPU was running at 312 MHz,
and the AP-SYS CPU was running at 52 MHz. Figure 12(b) is a snapshot taken when the
Dhrystone program has just started. Two hot spots are clearly observed.
Figure 12(c) is a snapshot when the local supply noise is at its maximum. Figure 12(d) is
an image taken when the AP-SYS CPU shows a supply “bounce” due to an inductive effect.
A typical situation where the APL-RT CPU executes Dhrystone while the AP-SYS CPU is
not operating but is consuming clock power is depicted in Fig. 12(e). Figure 12(f) is a
snapshot when both CPUs show a supply bounce due to an inductive effect. At this time, the
Dhrystone program was terminated, and both CPUs changed their operating modes, causing
large current changes.
It looks as if clock power consumption has vanished, although the
clock remains active.
3.2 Measurement of moving picture encoding
Another measurement example involves moving picture encoding. A hardware accelerator
that executes moving picture encoding and decoding (MPEG4) was implemented in this chip,
as shown in Fig. 9, and VMON5 was embedded in it.
The waveform measured by VMON5 is shown in Fig. 13. In this MPEG4-encoding operation,
a QCIF-size picture was encoded using the MPEG4 accelerator. In the measurement, the
APL-RT CPU was running at 312 MHz, and the AP-SYS CPU was running at 208 MHz.
The MPEG4 accelerator was running at 78 MHz, and V DD was1.25V.Thebasebandpartwas
powered on, but clock distribution was stopped.
MPEG4 encoding
17.1mV 30.9mV
Clock off
(d)
(a) (b)
(f)
(c)(e)
Initialization of MPEG4
20us/div 11.6mV/div
Fig. 13. Voltage noise measured while running MPEG encoding operation
 
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