added screencast link to lecture 7

commit 20f9168a5422fc13785dc0543a5adf1d5fceb959
Author: Chris Gregg <[email protected]>
Date:   Mon Oct 15 20:57:45 2018 -0700

    added screencast link to lecture 7

Author: tofergregg

_includes/schedule.html

@@ -146,7 +146,7 @@
             </tr>
             <tr>
                 <td>Lecture 7 (Mon): Communication and the Serial Protocol
-                    (<a href="lectures/07-Serial/serial.pdf">slides</a>--><!--, <a href="https://www.youtube.com/watch?v=NSX4izsY55I">screencast</a>-->, <a href="https://github.com/cs107e/cs107e.github.io/tree/master/lectures/Serial/code">code</a>)
+                    (<a href="lectures/07-Serial/serial.pdf">slides</a>, <a href="https://youtu.be/LErUamayHQk">screencast</a>, <a href="https://github.com/cs107e/cs107e.github.io/tree/master/lectures/Serial/code">code</a>)
                 </td>
                 <td>Read about characters and strings, basic IO (getc, putc, puts, printf), and structures (Section 1.5, 1.6, 1.9, 5.5, 6, 7 in K&amp;R; Section 3 in EssentialC).
                     Read about <a href="https://learn.sparkfun.com/tutorials/serial-communication/all">Serial Communication</a>.

lectures/07_Serial/code/sos/sos.c

@@ -0,0 +1,54 @@
+#include "gpio.h"
+#include "timer.h"
+
+#define PIN 20
+#define ONE_SECOND 1000
+#define DELAY_MORSE (ONE_SECOND/4)
+
+void morse_s();
+void morse_o();
+void dot();
+void dash();
+void morse_letter(char *code); // "--..-."
+
+void dot() {
+    gpio_write(PIN,1);
+    timer_delay_ms(DELAY_MORSE);
+    gpio_write(PIN,0);
+    timer_delay_ms(DELAY_MORSE);
+}
+
+void dash() {
+    gpio_write(PIN,1);
+    timer_delay_ms(DELAY_MORSE * 3);
+    gpio_write(PIN,0);
+    timer_delay_ms(DELAY_MORSE);
+}
+
+void morse_s() {
+    morse_letter("...");
+}
+
+void morse_o() {
+    morse_letter("---");
+}
+
+void morse_letter(char *code) {
+    while (*code) {
+        *code++ == '.' ? dot() : dash();
+    }
+}
+
+void main(void) {
+    timer_init();
+    gpio_init();
+    gpio_set_output(PIN);
+
+    while (1) {
+        // flash SOS
+        morse_s();
+        morse_o();
+        morse_s();
+        timer_delay_ms(DELAY_MORSE * 4);
+    }
+}