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<title>ring oscillator timing tests</title>
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<b>Ring Oscillators</b>
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This page collects ring oscillator timing tests for embedded systems (the prior page is <a href=prior/index.html>here</a>).

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<b>GPIO</b>
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The GPIO test measures how quickly pins can communicate with a processor core; this is relevant for implementing real-time algorithms that are not supported by processor peripherals. In this, two pins are connected; a bit is output on one, read on the other, inverted in software, and the loop repeated, with the frequency of the resulting oscillation reported. Twice this frequency is the rate of reading, modifying, and writing to pins (plus the loop overhead).

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<th>frequency (MHz)</th>
<th>processor</th>
<th>description</th>
<th>date</th>
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<tr>
<td>16.66</td>
<td>PocketBeagle</td>
<td><a href=GPIO/BeagleBoard/index.html>PRU</a></td>
<td>March, 2019</td>
</tr>

<tr>
<td>4.000</td>
<td>ATxmega8E5</td>
<td><a href=GPIO/ATxmega8E5/hello.ftdi.8E5.ring.c>VPORT</a></td>
<td>October, 2015</td>
</tr>

<tr>
<td>3.810</td>
<td>ESP32-WROOM</td>
<td><a href=GPIO/ESP32/ring.ESP32.ino>GPIO</a></td>
<td>December, 2020</td>
</tr>

<tr>
<td>3.737</td>
<td>ATSAMD51</td>
<td><a href=prior/gpio/atsamd51/index.html>PORT</a></td>
<td>November, 2018</td>
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<td>3.067</td>
<td>Raspberry Pi 4</td>
<td><a href=GPIO/bcm2835/ring.bcm2835.c>bcm2835, Buster</a></td>
<td>December, 2020</td>
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<td>2.528</td>
<td>ATSAMD11C</td>
<td><a href=GPIO/SAMD11C/ring.D11C.ino>IOBUS</a></td>
<td>November, 2020</td>
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<td>1.818</td>
<td>ATtiny412</td>
<td><a href=GPIO/ATtiny412/ring.t412.ino>VPORT</a></td>
<td>November, 2020</td>
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<td>1.171</td>
<td>ATSAMD11C</td>
<td><a href=GPIO/SAMD11C/ring.D11C.ino>PORT</a></td>
<td>November, 2020</td>
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<td>1.056</td>
<td>ATtiny412</td>
<td><a href=GPIO/ATtiny412/ring.t412.ino>PORT</a></td>
<td>November, 2020</td>
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<td>0.358</td>
<td>ATtiny412</td>
<td><a href=GPIO/ATtiny412/ring.t412.ino>digitalRead/Write</a></td>
<td>November, 2020</td>
</tr>

<tr>
<td>0.153</td>
<td>Raspberry Pi 4</td>
<td><a href=GPIO/libgpiod/ring.libgpiod.c>libgpiod, Buster</a></td>
<td>December, 2020</td>
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<td>0.153</td>
<td>Raspberry Pi 4</td>
<td><a href=GPIO/gpiolib/ring.gpiolib.c>gpiolib, Buster</a></td>
<td>December, 2020</td>
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