Set up the system clock to use crystal, and PLL to 80MHz

diff --git a/led_blink.c b/led_blink.c
index 14ee0d1..657255a 100644 (file)
--- a/led_blink.c
+++ b/led_blink.c
@@ -5,6 +5,29 @@ static void spin(int);
 
 __attribute__((isr))
 void main_isr() {
+       // Power on the PLL, set to 16MHz XTAL
+       SYSCTL_RCC_R &= ~(SYSCTL_RCC_PWRDN | SYSCTL_RCC_XTAL_M);
+       SYSCTL_RCC_R |= SYSCTL_RCC_XTAL_16MHZ;
+
+       // Choose the main oscillator
+       SYSCTL_RCC_R &= ~(SYSCTL_RCC_MOSCDIS | SYSCTL_RCC_OSCSRC_M);
+
+       // Wait for PLL to come up
+       while (!SYSCTL_PLLSTAT_R & SYSCTL_PLLSTAT_LOCK) {
+               asm("");
+       }
+
+       // Choose the PLL, at 80MHz
+       // Must re-do the OSCSRC, PWRDN configuration from RCC into RCC2, so
+       // that we don't interrupt what we've already configured.
+       int rcc2 = SYSCTL_RCC2_R;
+       rcc2 &= ~(SYSCTL_RCC2_SYSDIV2_M | SYSCTL_RCC2_SYSDIV2LSB |
+                 SYSCTL_RCC2_PWRDN2 | SYSCTL_RCC2_BYPASS2 |
+                 SYSCTL_RCC2_OSCSRC2_M);
+       rcc2 |= SYSCTL_RCC2_USERCC2 | SYSCTL_RCC2_DIV400 |
+               (2 << SYSCTL_RCC2_SYSDIV2_S);
+       SYSCTL_RCC2_R = rcc2;
+
        // Enable Port F
        SYSCTL_RCGCGPIO_R = 0x20;