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diff --git a/RaspberryPiZeroW_bcm2835/index.html b/RaspberryPiZeroW_bcm2835/index.html
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+<html>
+<head>
+<style>
+pre code {
+ background-color: #eee;
+ border: 1px solid #999;
+ display: block;
+ padding: 20px;
+}
+</style>
+
+
+</head>
+<body>
+
+<h1>RaspberryPi Zero W with BMC2835</h1>
+
+<figure>
+<img src='bcm2835-06ma.png'>
+<figcaption>Ring oscillator with 6mA pad current.</figcaption>
+</figure>
+
+<p>This ring oscillator uses the <a href='http://www.airspayce.com/mikem/bcm2835/index.html'>BCM2835 library</a> from Mike McCauley. The code is available <a href='ring.c'>here</a>, or visible below.</p>
+
+<pre>
+<code>
+//build:
+// gcc -o ring ring.c -l bcm2835
+//run:
+// sudo ./ring
+#include <bcm2835.h>
+#include <stdio.h>
+#define PIN_OUT RPI_GPIO_P1_11
+#define PIN_IN RPI_GPIO_P1_15
+
+int main(int argc, char **argv)
+{
+ if (!bcm2835_init())
+ return 1;
+
+ //set changing pad current can change ringing characteristics on pulses
+ bcm2835_gpio_set_pad(BCM2835_PAD_GROUP_GPIO_0_27, BCM2835_PAD_DRIVE_6mA);
+
+ //this block is supposed to prevent kernel swapping
+ //I didn't get it to compile...
+ //struct sched_param sp;
+ //memset(&sp, 0, sizeof(sp));
+ //sp.sched_priority = sched_get_priority_max(SCHED_FIFO);
+ //sched_setscheduler(0, SCHED_FIFO, &sp);
+ //mlockall(MCL_CURRENT | MCL_FUTURE);
+
+ bcm2835_gpio_fsel(PIN_OUT, BCM2835_GPIO_FSEL_OUTP);
+ bcm2835_gpio_fsel(PIN_IN , BCM2835_GPIO_FSEL_INPT);
+ //bcm2835_gpio_set_pud(PIN_IN, BCM2835_GPIO_PUD_UP);
+ while (1)
+ bcm2835_gpio_write(PIN_OUT, 1-bcm2835_gpio_lev(PIN_IN) );
+ bcm2835_close();
+ return 0;
+}
+</code>
+</pre>
+
+<p>We can change the pad current to improve the ringing of the pulses:</p>
+<figure>
+<img src='bcm2835-16ma.png'>
+<img src='bcm2835-02ma.png'>
+<figcaption>A) 16mA pad current, B) 2 mA pad current</figcaption>
+</figure>
+
+</body>
+
+</html>
\ No newline at end of file
diff --git a/RaspberryPiZeroW_bcm2835/ring.c b/RaspberryPiZeroW_bcm2835/ring.c
new file mode 100644
index 0000000000000000000000000000000000000000..320b448a61dae30dd7abb723b7f978f8677ee07f
--- /dev/null
+++ b/RaspberryPiZeroW_bcm2835/ring.c
@@ -0,0 +1,34 @@
+//build:
+// gcc -o ring ring.c -l bcm2835
+//run:
+// sudo ./ring
+#include <bcm2835.h>
+#include <stdio.h>
+#define PIN_OUT RPI_GPIO_P1_11
+#define PIN_IN RPI_GPIO_P1_15
+
+int main(int argc, char **argv)
+{
+ if (!bcm2835_init())
+ return 1;
+
+ //set changing pad current can change ringing characteristics on pulses
+ bcm2835_gpio_set_pad(BCM2835_PAD_GROUP_GPIO_0_27, BCM2835_PAD_DRIVE_6mA);
+
+ //this block is supposed to prevent kernel swapping
+ //I didn't get it to compile...
+ //struct sched_param sp;
+ //memset(&sp, 0, sizeof(sp));
+ //sp.sched_priority = sched_get_priority_max(SCHED_FIFO);
+ //sched_setscheduler(0, SCHED_FIFO, &sp);
+ //mlockall(MCL_CURRENT | MCL_FUTURE);
+
+ bcm2835_gpio_fsel(PIN_OUT, BCM2835_GPIO_FSEL_OUTP);
+ bcm2835_gpio_fsel(PIN_IN , BCM2835_GPIO_FSEL_INPT);
+ //bcm2835_gpio_set_pud(PIN_IN, BCM2835_GPIO_PUD_UP);
+ while (1)
+ bcm2835_gpio_write(PIN_OUT, 1-bcm2835_gpio_lev(PIN_IN) );
+ bcm2835_close();
+ return 0;
+}
+