Add comments and clean up.

[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..fcb46c4b29dd06c5454eebf8ad05366e10848abb 100644 (file)
--- a/bertos/cpu/cortex-m3/drv/clock_sam3.c
+++ b/bertos/cpu/cortex-m3/drv/clock_sam3.c
@@ -30,13 +30,117 @@
  *
  * -->
  *
- * \brief AT91SAM3 clocking driver.
+ * \brief Atmel SAM3 clock setup.
  *
  * \author Stefano Fedrigo <aleph@develer.com>
  */
 
 #include "clock_sam3.h"
+#include <cfg/compiler.h>
+#include <cfg/macros.h>
+#include <io/sam3.h>
+
+
+/* Frequency of board main oscillator */
+#define BOARDOSC_FREQ  12000000
+
+/* Timer countdown timeout for clock initialization operations */
+#define CLOCK_TIMEOUT    0xFFFFFFFF
+
+
+#if CPU_FREQ == 84000000 || CPU_FREQ == 48000000
+
+INLINE uint32_t evaluate_pll(void)
+{
+       return CKGR_PLLR_MUL(CPU_FREQ / BOARDOSC_FREQ * 2 - 1) | CKGR_PLLR_DIV(2);
+}
+
+#else
+
+#warning CPU clock frequency non-standard setting: multiplier and divider values \
+ will be computed at runtime: effective computed frequency could be different \
+ from expected.
+
+/*
+ * 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.  Start with higher multipliers and divisors, generally better.
+ */
+INLINE uint32_t evaluate_pll(void)
+{
+       int mul, div, best_mul, best_div;
+       int best_delta = CPU_FREQ;
+       int freq = 0;
+
+       for (mul = 13; mul > 0; mul--)
+       {
+               for (div = 24; div > 0; div--)
+               {
+                       freq = BOARDOSC_FREQ / div * (1 + mul);
+                       if (ABS((int)CPU_FREQ - freq) < best_delta) {
+                               best_delta = ABS((int)CPU_FREQ - freq);
+                               best_mul = mul;
+                               best_div = div;
+                       }
+               }
+       }
+
+       return CKGR_PLLR_DIV(best_div) | CKGR_PLLR_MUL(best_mul);
+}
+
+#endif /* CPU_FREQ */
 
 void clock_init(void)
 {
+       uint32_t timeout;
+
+       /* Disable watchdog */
+       WDT_MR = BV(WDT_WDDIS);
+
+       /* Set wait states for flash access, needed for higher CPU clock rates */
+       EEFC0_FMR = EEFC_FMR_FWS(3);
+#ifdef EEFC1_FMR
+       EEFC1_FMR = EEFC_FMR_FWS(3);
+#endif
+
+       // Initialize main oscillator
+       if (!(CKGR_MOR & BV(CKGR_MOR_MOSCSEL)))
+       {
+               CKGR_MOR = CKGR_MOR_KEY(0x37) | CKGR_MOR_MOSCXTST(0x8)
+                       | BV(CKGR_MOR_MOSCRCEN) | BV(CKGR_MOR_MOSCXTEN);
+               timeout = CLOCK_TIMEOUT;
+               while (!(PMC_SR & BV(PMC_SR_MOSCXTS)) && --timeout);
+       }
+
+       // Switch to external oscillator
+       CKGR_MOR = CKGR_MOR_KEY(0x37) | CKGR_MOR_MOSCXTST(0x8)
+               | BV(CKGR_MOR_MOSCRCEN) | BV(CKGR_MOR_MOSCXTEN) | BV(CKGR_MOR_MOSCSEL);
+       timeout = CLOCK_TIMEOUT;
+       while (!(PMC_SR & BV(PMC_SR_MOSCXTS)) && --timeout);
+
+       // Initialize and enable PLL clock
+       CKGR_PLLR = evaluate_pll() | BV(CKGR_PLLR_STUCKTO1) | CKGR_PLLR_PLLCOUNT(0x2);
+       timeout = CLOCK_TIMEOUT;
+       while (!(PMC_SR & BV(PMC_SR_LOCK)) && --timeout);
+
+       PMC_MCKR = PMC_MCKR_CSS_MAIN_CLK;
+       timeout = CLOCK_TIMEOUT;
+       while (!(PMC_SR & BV(PMC_SR_MCKRDY)) && --timeout);
+
+       PMC_MCKR = PMC_MCKR_CSS_PLL_CLK;
+       timeout = CLOCK_TIMEOUT;
+       while (!(PMC_SR & BV(PMC_SR_MCKRDY)) && --timeout);
+
+       /* Enable clock on PIO for inputs */
+       // TODO: move this in gpio_init() for better power management?
+       pmc_periphEnable(PIOA_ID);
+       pmc_periphEnable(PIOB_ID);
+       pmc_periphEnable(PIOC_ID);
+#ifdef PIOF_ID
+       pmc_periphEnable(PIOD_ID);
+       pmc_periphEnable(PIOE_ID);
+       pmc_periphEnable(PIOF_ID);
+#endif
 }