Add serial I/O.

- Reset device when receiving '#' from the UART.
- Send some hello strings via the UART.

blink.c

@@ -1,64 +1,129 @@
+/*
+ * A simple test program for testing lowlevel access to the MSS310's
+ * - LEDs (green LED, red LED)
+ * - Button
+ * - UART (debug pins)
+ *
+ * When run on the MSS310, this program:
+ * - cycles through all LED colors (red/green/yellow)
+ * - prints some text on the serial console
+ * - resets the CPU when the button on the device is pressed
+ * - resets the CPU when the # key is sent via the serial interface
+ */
+
 #include <stdint.h>
 
-#define RSTCTL          0x10000034
-#define GPIO2_MODE      0x10000064
-#define GPIO_CTRL_1     0x10000604
-#define GPIO_DATA_1     0x10000624
-#define GPIO_DSET_1     0x10000634
-#define GPIO_DCLR_1     0x10000644
+#define RSTCTL          0x10000034      /* Reset control register */
+
+#define GPIO2_MODE      0x10000064      /* GPIO2 purpose selection */
+
+#define GPIO_CTRL_1     0x10000604      /* Direction control register */
+#define GPIO_DATA_1     0x10000624      /* Data register              */
+#define GPIO_DSET_1     0x10000634      /* Data set register          */
+#define GPIO_DCLR_1     0x10000644      /* Data clear register        */
+
+/* UART is expected to be configured from u-boot already */
+#define UART0_RBR       0x10000C00      /* RX buffer register   */
+#define UART0_THR       0x10000C00      /* TX holding register  */
+#define UART0_LSR       0x10000C14      /* Line status register */
 
-#define SYS_RST            (1 << 0)
+#define UART_LSR_DR        (1 << 0)     /* Data ready                */
+#define UART_LSR_THRE      (1 << 5)     /* TX holding register empty */
+
+#define SYS_RST            (1 << 0)     /* Whole system reset */
 
 #define GPIO_RELAY         (1 << 0)
 #define GPIO_LED_PIN_RED   (1 << 1)
 #define GPIO_LED_PIN_GREEN (1 << 2)
 #define GPIO_BUTTON        (1 << 3)
 
+
 static inline void write_l(unsigned int addr, unsigned int val)
 {
     volatile uint32_t *ptr = (uint32_t *)(addr);
     *ptr = val;
 }
 
+
 static inline unsigned int read_l(unsigned int addr)
 {
     volatile uint32_t *ptr = (uint32_t *)(addr);
     return *ptr;
 }
 
+
+static inline void reset_cpu()
+{
+  write_l(RSTCTL, SYS_RST);
+}
+
+
 static void reset_if_button_pressed()
 {
+    /* Button is pressed if port is low */
     if (!(read_l(GPIO_DATA_1) & GPIO_BUTTON)) {
-        write_l(RSTCTL, SYS_RST);
+      reset_cpu();
     }
 }
 
+
+static void reset_if_hash_received()
+{
+    if (read_l(UART0_LSR) & UART_LSR_DR) {
+        /* Something in the RX buffer */
+        if ((read_l(UART0_RBR) & 0xFF) == '#') {
+            reset_cpu();
+        }
+    }
+}
+
+/* A very dumb delay routine */
 static void delay()
 {
     volatile int i, j;
     for (i = 0; i < 500; i++) {
         reset_if_button_pressed();
+        reset_if_hash_received();
         for (j = 0; j < 500; j++) {
             /* Do nothing */
         }
     }
 }
 
+
+/* Send the given string to the UART */
+static void print_string(const char *s)
+{
+    const char *p;
+
+    for (p = s; *p; ++p) {
+        while ((read_l(UART0_LSR) & UART_LSR_THRE) == 0) {
+            /* Wait until there's some space in the FIFO */
+        }
+        write_l(UART0_THR, *p);
+    }
+}
+
 #ifdef __cplusplus
 extern "C"
 #endif
 void entrypoint(void)
 {
-    write_l(GPIO2_MODE, 0x05550550);
+    write_l(GPIO2_MODE, 0x05550550);  /* Value determined from original app */
+    /* Configure GPIO pins as outpu */
     write_l(GPIO_CTRL_1, GPIO_RELAY | GPIO_LED_PIN_RED | GPIO_LED_PIN_GREEN);
     while (1) {
         write_l(GPIO_DCLR_1, GPIO_LED_PIN_RED);
         delay();
+        print_string("Hello 1\r\n");
         write_l(GPIO_DCLR_1, GPIO_LED_PIN_GREEN);
         delay();
+        print_string("Hello 2\r\n");
         write_l(GPIO_DSET_1, GPIO_LED_PIN_RED);
         delay();
+        print_string("Hello 3\r\n");
         write_l(GPIO_DSET_1, GPIO_LED_PIN_GREEN);
         delay();
+        print_string("Hello 4\r\n");
     }
 }