diff --git a/gpio/atsamd51/index.html b/gpio/atsamd51/index.html
new file mode 100644
index 0000000000000000000000000000000000000000..a86988becf05915e16230d5285d6e76c4c48d4a0
--- /dev/null
+++ b/gpio/atsamd51/index.html
@@ -0,0 +1,89 @@
+<html>
+<head>
+<style>
+pre code {
+ background-color: #eee;
+ border: 1px solid #999;
+ display: block;
+ padding: 20px;
+}
+</style>
+
+
+</head>
+<body>
+
+<h1>ATSAMD51</h1>
+
+<figure>
+<img src='ring.jpg' height=50%>
+<figcaption>Ring oscillator with ATSAMD51J19</figcaption>
+</figure>
+
+<p>This ring oscillator runs on the ATSAMD51J19 MCU using the Adafruit Feather dev board. The ATSAMD51J19 has an ARM Cortex-M4 running with a max speed of 120 MHz. Code for the oscillator is available <a href='ring.ino'>here</a>, or visible below.</p>
+
+<pre>
+<code>
+#define portin PORT->Group[PORTA].IN.reg
+#define outclr PORT->Group[PORTA].OUTCLR.reg
+#define outset PORT->Group[PORTA].OUTSET.reg
+#define out PORT->Group[PORTA].OUT.reg
+#define outtgl PORT->Group[PORTA].OUTTGL.reg
+
+
+const uint8_t in_pin = 21;
+const uint32_t in_mask = 1ul<<in_pin;
+const uint8_t out_pin = 22;
+const uint32_t out_mask = 1ul<<out_pin;
+
+void setup() {
+
+ // Set pin mode according to chapter '32.6.3 I/O Pin Configuration'
+ // enable input, to support reading back values, with pullups disabled
+ PORT->Group[PORTA].PINCFG[out_pin].reg = (uint8_t)(PORT_PINCFG_INEN) ;
+ // Set pin to output mode
+ PORT->Group[PORTA].DIRSET.reg = out_mask;
+ // Set in pin to input mode
+ PORT->Group[PORTA].PINCFG[in_pin].reg=(uint8_t)(PORT_PINCFG_INEN) ;
+ PORT->Group[PORTA].DIRCLR.reg = in_pin ;
+
+ //make sure port synchronizer always active, else we'll use extra clock cycles.
+ //I'm not sure I'm activating the synchronizer correctly, because I don't see a change when I add this...
+ PORT->Group[PORTA].CTRL.reg = in_mask;
+
+ //loop
+ while(1){
+ //ternary operator: assymetric 300ns (200-100)
+ //portin & in_mask ? outclr = out_mask : outset = out_mask;
+ //portin & in_mask ? outclr = out_mask : out = out_mask;
+
+ //full port inversion: symmetric 300ns
+ out = ~(portin);
+
+ //bitwise xor: 300ns
+ //out = ((portin ^ in_mask) << 1);
+
+ //if else, 300ns
+ /*if (portin & in_mask){
+ outclr = out_mask;
+ } else {
+ outset = out_mask;
+ }*/
+ }
+}
+
+void loop() {}
+</code>
+</pre>
+
+<p>By default the port consumes extra clock cycles to save power and only sample the input pin when a read is requested (see description below). We can set the input synchronizer to always be active to avoid this delay. I've tried to do this above, but I need to confirm if this was successful.</p>
+
+<img src='port-diagram.png' height=200px>
+<img src='input-synchronization.png' height=200px>
+
+
+<p><a href='../../index.html'>Back</a></p>
+
+</body>
+
+</html>
\ No newline at end of file
diff --git a/gpio/atsamd51/input-synchronization.png b/gpio/atsamd51/input-synchronization.png
new file mode 100644
index 0000000000000000000000000000000000000000..b97ebca00303cc3b77dadea50d69a815dece8d7a
Binary files /dev/null and b/gpio/atsamd51/input-synchronization.png differ
diff --git a/gpio/atsamd51/port-diagram.png b/gpio/atsamd51/port-diagram.png
new file mode 100644
index 0000000000000000000000000000000000000000..d0b534c15bb52229df521044544d4d129f9301ed
Binary files /dev/null and b/gpio/atsamd51/port-diagram.png differ
diff --git a/gpio/atsamd51/ring.ino b/gpio/atsamd51/ring.ino
new file mode 100644
index 0000000000000000000000000000000000000000..a057eef4f3837b4d790c7bedb072c6571d7bda75
--- /dev/null
+++ b/gpio/atsamd51/ring.ino
@@ -0,0 +1,68 @@
+#define portin PORT->Group[PORTA].IN.reg
+#define outclr PORT->Group[PORTA].OUTCLR.reg
+#define outset PORT->Group[PORTA].OUTSET.reg
+#define out PORT->Group[PORTA].OUT.reg
+#define outtgl PORT->Group[PORTA].OUTTGL.reg
+
+//11: { PORTA, 21, PIO_TCC_PDEC, (PIN_ATTR_DIGITAL|PIN_ATTR_PWM|PIN_ATTR_TIMER), No_ADC_Channel, PWM0_CH1, TCC0_CH1, EXTERNAL_INT_5 },
+const uint8_t in_pin = 21;
+const uint32_t in_mask = 1ul<<in_pin;
+//12: { PORTA, 22, PIO_TCC_PDEC, (PIN_ATTR_DIGITAL|PIN_ATTR_PWM|PIN_ATTR_TIMER), No_ADC_Channel, PWM0_CH2, TCC0_CH2, EXTERNAL_INT_6 },
+const uint8_t out_pin = 22;
+const uint32_t out_mask = 1ul<<out_pin;
+//led:{ PORTA, 23, PIO_TCC_PDEC, (PIN_ATTR_DIGITAL|PIN_ATTR_PWM|PIN_ATTR_TIMER), No_ADC_Channel, PWM0_CH3, TCC0_CH3, EXTERNAL_INT_7 }, // TCC2/WO[1]
+//const uint32_t out_mask = 1ul<<23;
+
+void setup() {
+ //set clock port for digital io
+ //PM->APBBMASK.reg |= PM_APBBMASK_PORT ;
+
+
+ // Set pin mode according to chapter '32.6.3 I/O Pin Configuration'
+ // enable input, to support reading back values, with pullups disabled
+ PORT->Group[PORTA].PINCFG[out_pin].reg = (uint8_t)(PORT_PINCFG_INEN) ;
+ // Set pin to output mode
+ PORT->Group[PORTA].DIRSET.reg = out_mask;
+ // Set in pin to input mode
+ PORT->Group[PORTA].PINCFG[in_pin].reg=(uint8_t)(PORT_PINCFG_INEN) ;
+ PORT->Group[PORTA].DIRCLR.reg = in_pin ;
+ PORT->Group[PORTA].CTRL.reg = in_mask; //make sure port synchronizer always active
+
+
+ while(1){
+ /*PORT->Group[PORTA].OUTSET.reg = out_mask; // turn on led
+ delay(1000); // wait for a second
+ PORT->Group[PORTA].OUTCLR.reg = out_mask; // turn off led
+ delay(1000); // wait for a second
+ */
+
+ //ternary operator: assymetric 300ns (200-100)
+ //portin & in_mask ? outclr = out_mask : outset = out_mask;
+ //portin & in_mask ? outclr = out_mask : out = out_mask;
+ out = ~(portin);
+
+
+ //bitwise xor: 300ns
+ //out = ((portin ^ in_mask) << 1);
+
+ //if else
+ /*if (portin & in_mask){
+ outclr = out_mask;
+ } else {
+ outset = out_mask;
+ }*/
+
+ //toggle, 10 mhz
+ //outtgl = out_mask;
+
+ //manual toggle, 20mhz
+ //outclr = out_mask;
+ //outset = out_mask;
+
+
+ }
+
+
+}
+
+void loop() {}
diff --git a/gpio/atsamd51/ring.jpg b/gpio/atsamd51/ring.jpg
new file mode 100644
index 0000000000000000000000000000000000000000..e37353cf41cd6342e28c55209aaac3f917fb13e6
Binary files /dev/null and b/gpio/atsamd51/ring.jpg differ
diff --git a/ring.json b/ring.json
index d5598693274bbc14214f05598dc8f866b7db9100..d46ebadff5d9047e4894b3d03d55bac4b760fd88 100644
--- a/ring.json
+++ b/ring.json
@@ -7,6 +7,7 @@
"dev_board_sales_link":"link for dev board purchase",
"ic_price":"price for bare ic, dollars",
"ic_sales_link":"link for ic purchase",
+ "cpu_frequency":"clock speed in MHz",
"ring_period":"period of one full ring oscillator waveform, in microseconds"
},
@@ -63,6 +64,17 @@
}
],
"gpio":[
+ {
+ "name":"ATSAMD51",
+ "serial_number":"",
+ "subdirectory_path":"gpio/atsamd51",
+ "dev_board_price":14.95,
+ "dev_board_sales link":"https://www.adafruit.com/product/3800",
+ "ic_price":4.31,
+ "ic_sales_link":"ATSAMD51J19A-AUTCT-ND",
+ "cpu_frequency":120,
+ "ring_period":0.27
+ },
{
"name":"ATSAMS70",
"serial_number":"",