fix(Lab 2):

Added:
- Buffer SIZE and clearing
- Enabled GP15 pull-up resistor

Modified:
- Sleep time according to Lab instruction
- Variables to unsigned char

.gitignore

@@ -269,4 +269,5 @@ gen
 
 # Android studio 3.1+ serialized cache file
 
-*/build/*
+*/build/*
+*/*.cmake

lab_2/lab_2.c

@@ -1,7 +1,8 @@
 /**
  * Lab 2
- * Note that this program would print out garbage for the first few characters
+ * This is configured with GPIO15 as a pseudo button with a pull up resistor
- * received. It will work as intended after a few characters are received.
+ * Since the button is active low, the program will send '1' when the button is not pressed (high)
+ * and send 'A' to 'Z' when the button is pressed (low)
  */
 
 #include <stdio.h>
@@ -9,12 +10,13 @@
 
 #define UART_ID uart0
 #define BAUD_RATE 115200    // Baud rate of UART
+#define UART_BUF_SIZE 64    // Buffer size for UART
 
 #define UART_TX_PIN 16      // GPIO for UART TX pin
 #define UART_RX_PIN 17      // GPIO for UART RX pin
-#define GPIO_PIN 15         // GPIO for pseudo button
+#define PSEUDO_BTN 15       // GPIO for pseudo button
 
-#define SLEEP_TIME 100     // For testing can use a smaller value
+#define SLEEP_TIME 1000     // For testing can use a smaller value
                             // 1000ms is based on the lab requirements
 
 /**
@@ -22,24 +24,32 @@
  * @param uart_input  Pointer to a character to be sent through UART0 (Space optimisation)
  * @return void       Prints the character in uart_receive()
  */
-void uart_transmit(char *uart_input) {
+static void uart_transmit(char *uart_input) {
-    if (gpio_get(GPIO_PIN)) {           // Active low
+    if (gpio_get(PSEUDO_BTN)) {             // If GPIO15 is high
         uart_putc(UART_ID, '1');
-    } else {                                // Active high
+    } else {                                     // If GPIO15 is low
         uart_putc(UART_ID, *uart_input);
-        *uart_input = (*uart_input - 'A' + 1) % 26 + 'A'; // Next character
+        *uart_input = (*uart_input - 'A' + 1) % 26 + 'A'; // Next character and wrap around back to A
-                                                          // Wrap around back to A
     }
 }
 
+/**
+ * Clear buffer (read until buffer size is UART_BUF_SIZE)
+ * This is to prevent the program from printing out garbage
+ * for the first few characters received or during pseudo button press
+ * @return void
+ */
+static void uart_buf_clr() {
+    while (uart_is_readable(UART_ID) && uart_getc(UART_ID) != UART_BUF_SIZE);
+}
+
 /**
  * Receives a character through UART0 and prints it out
- * Ideally, the buffer should be cleared after each read
  * NOTE: Flipping bit 5 effectively converts a character to lowercase
  * @param uart_output Pointer to a location to store the received character (Space optimisation)
  * @return void       Character is read and printed
  */
-void uart_receive(char *uart_output) {
+static void uart_receive(char *uart_output) {
     if (uart_is_readable(UART_ID)) {
         *uart_output = uart_getc(UART_ID);
 
@@ -50,6 +60,8 @@ void uart_receive(char *uart_output) {
             *uart_output = '2';         // If '1' is received, print '2'
         }
 
+        uart_buf_clr();                 // Clear buffer
+
         printf("%c\n", *uart_output);
     }
 }
@@ -58,22 +70,25 @@ void uart_receive(char *uart_output) {
  * Initializes UART0 and GPIO pins
  * @return void
  */
-void pin_init() {
+static void pin_init() {
     // UART init
     uart_init(UART_ID, BAUD_RATE);
     gpio_set_function(UART_TX_PIN, GPIO_FUNC_UART);
     gpio_set_function(UART_RX_PIN, GPIO_FUNC_UART);
 
     // Pseudo button init
-    gpio_set_dir(GPIO_PIN, GPIO_IN);
+    gpio_set_dir(PSEUDO_BTN, GPIO_IN);
+
+    // Enable pull up resistor
+    gpio_set_pulls(PSEUDO_BTN, true, false);
 }
 
 int main() {
     stdio_init_all();
     pin_init();
 
-    char uart_input = 'A'; // Initial value of A
+    u_char uart_input = 'A'; // Initial value of A
-    char uart_output;      // To store received character
+    u_char uart_output;      // To store received character
 
     while (true) {
         uart_transmit(&uart_input); // Pass by reference to change
@@ -82,7 +97,7 @@ int main() {
         uart_receive(&uart_output); // Pass by reference to change
                                     // value of uart_output during reception
 
-        sleep_ms(SLEEP_TIME); // Sleep based on SLEEP_TIME
+        sleep_ms(SLEEP_TIME);   // Sleep based on SLEEP_TIME
     }
 
 }