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will_84
0 Posts |
 Posted - 04 Sep 2007 : 11:00:34
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I'm looking for a good place on the BitsyXb board to measure CPU power fluctuations when transitioning from low power states to full power.
I found the +5V VCC on the J3 connector from the reference manual, but I was wondering if there was a better place to isolate the measurement to the CPU. Right now I'm using a simple DAQ board, so I don't have the capability of measuring the draw directly off of the PXA's pinout due to wiring precision. |
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grenierm
133 Posts |
Posted - 05 Sep 2007 : 15:57:26
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Hi, thanks for the question, and sorry for the delayed response.
In order to get a better signal from the processor during low power to high power transitions (such as wake-up from suspend mode) try probing the POWERENABLE line, which is pin 41 on connector J3.
Keep in mind that the pins are numbered such that pin 1 has a square pad, which can be seen from the bottom of the board, and the column of pins associated with pin 1 represents all the odd pin numbers.
Hope this helps. |
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grenierm
133 Posts |
Posted - 06 Sep 2007 : 12:51:46
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Another option (and likely more relevent than the above response) would be to place your multimeter in series with the 12V line, found on header J16, pin 1, on the connector board.
Also, it would be smart to disconnect all peripherals such as backlight, display and touchscreen, etc. |
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will_84
0 Posts |
Posted - 11 Sep 2007 : 15:28:09
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Thank you for the reply, yes, I initially had good results with the 12V line in power from the external AC transformer using a simple multimeter, unfortunately my DAQ board (www.mccdaq.com USB-1208LS) has a 10V threshold for DC voltages.
Idealistically I would like to measure just the CPU's voltage, however if there is not a suitable location for this, I suspect that the board's +/- 10V AC mode can be made to work effectively as +20V DC with a common ground and reference. |
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grenierm
133 Posts |
Posted - 11 Sep 2007 : 17:32:13
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In this case, the core voltage for the CPU (1.8V DC) can be measured by probing the output of the linear voltage regulator. Probe at pin 5, on U55.
In order to find U55, flip the BitsyXb over so that the bottom of the board is facing you lengthwise with the Atmel Atmega8535L IC near the top of the board. Go up from the Atmega8535L IC about an inch and you'll find U55, (it's a 5 pin regulator) and pin 5 is the top-left pin)
Let me know if you have any trouble finding this location. |
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will_84
0 Posts |
Posted - 12 Sep 2007 : 10:48:02
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| I was able to identify the regulator, and pin 5, and it is strictly for the CPU? |
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grenierm
133 Posts |
Posted - 12 Sep 2007 : 14:15:30
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Yes, this linear regulator is for the Processor Core Voltage.
Also, more useful information about Power Supply Characteristics can be found in the BitsyXb User Manual, under section 6.3.4 |
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will_84
0 Posts |
Posted - 08 Oct 2007 : 17:07:30
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Thanks for the manual reference, it was able to clarify my terminology,
My interest is in the VDDI processor core voltage mentioned in 6.3.4, it's my understanding that the processor frequency and this voltage are interrelated, and using some cpufreq drivers on my side I'm attempting to measure the impact on power consumption.
The U55 regulator unfortunately remains constant throughout frequency changes, is there a reference location for VDDI on board? |
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grenierm
133 Posts |
Posted - 08 Oct 2007 : 18:16:05
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Hi Will_84,
A better reference for the VDDI processor core voltage is on the output of inductor L12.
I have just emailed you a graphic of the location on the BitsyXb, you'll want to use the left side of L12, this is the inductor output. |
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