sam3n port: add code to setup system clock

[bertos.git] / bertos / cpu / cortex-m3 / drv / clock_sam3.c

diff --git a/bertos/cpu/cortex-m3/drv/clock_sam3.c b/bertos/cpu/cortex-m3/drv/clock_sam3.c
index 967e3798b6613429ef293e4675b8ed78286f9601..ae70d52999ae20b35574f792aac35c0e7a7fd2ba 100644 (file)
--- a/bertos/cpu/cortex-m3/drv/clock_sam3.c
+++ b/bertos/cpu/cortex-m3/drv/clock_sam3.c
@@ -36,7 +36,58 @@
  */
 
 #include "clock_sam3.h"
+#include <io/sam3_pmc.h>
+#include <cfg/compiler.h>
+#include <cfg/macros.h>
+
+/* Value to use when writing CKGR_MOR, to unlock write */
+#define CKGR_KEY  0x37
+
+/*
+ * Try to evaluate the correct divider and multiplier value depending
+ * on the desired CPU frequency.
+ *
+ * We try all combinations in a certain range of divider and multiplier
+ * values.  The range can change, with better match with "strange"
+ * frequencies, but boot time will be longer.
+ *
+ * Limits for SAM3N: divider [1,255], multiplier [1,2047].
+ */
+INLINE uint32_t evaluate_pll(void)
+{
+       int mul, div, best_mul, best_div;
+       int best_delta = CPU_FREQ;
+       int freq = 0;
+
+       for (mul = 1; mul <= 8; mul++)
+       {
+               for (div = 1; div <= 24; div++)
+               {
+                       // RC oscillator set to 12 MHz
+                       freq = 12000000 / div * (1 + mul);
+                       if (ABS(CPU_FREQ - freq) < best_delta) {
+                               best_delta = ABS(CPU_FREQ - freq);
+                               best_mul = mul;
+                               best_div = div;
+                       }
+               }
+       }
+
+       // Bit 29 must always be set to 1
+       return CKGR_PLLR_DIV(best_div) | CKGR_PLLR_MUL(best_mul) | BV(29);
+}
+
 
 void clock_init(void)
 {
+       /* Enable and configure internal Fast RC oscillator */
+       CKGR_MOR_R =
+               CKGR_MOR_KEY(CKGR_KEY)       // Unlock key
+               | CKGR_MOR_MOSCRCEN          // Main On-Chip RC oscillator enable
+               | CKGR_MOR_MOSCRCF_12MHZ;    // RC oscillator frequency
+
+       /* Master clock: select PLL clock and no prescaling */
+       PMC_MCKR_R = PMC_MCKR_CSS_PLL_CLK;
+
+       CKGR_PLLR_R = evaluate_pll();
 }