*
* -->
*
- * \brief AT91SAM3 clocking driver.
+ * \brief ATSAM3 clock setup.
*
* \author Stefano Fedrigo <aleph@develer.com>
*/
#include "clock_sam3.h"
-#include <io/sam3_pmc.h>
#include <cfg/compiler.h>
#include <cfg/macros.h>
+#include <io/sam3_pmc.h>
+#include <io/sam3_sysctl.h>
+#include <io/sam3_flash.h>
+#include <io/sam3_wdt.h>
+
+
+/* Frequency of board main oscillator */
+#define BOARDOSC_FREQ 12000000
+
+/* Main crystal oscillator startup time, optimal value for CPU_FREQ == 48 MHz */
+#define BOARD_OSC_COUNT (CKGR_MOR_MOSCXTST(0x8))
+
+/* Timer countdown timeout for clock initialization operations */
+#define CLOCK_TIMEOUT 0xFFFFFFFF
-/* Value to use when writing CKGR_MOR, to unlock write */
-#define CKGR_KEY 0x37
/*
* Try to evaluate the correct divider and multiplier value depending
{
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);
+ 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;
}
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
+ uint32_t timeout;
+
+ /* Disable watchdog */
+ WDT_MR = BV(WDT_WDDIS);
+
+ /* Set 4 wait states for flash access, needed for higher CPU clock rates */
+ EEFC_FMR = EEFC_FMR_FWS(3);
+
+ // Select external slow clock
+ if (!(SUPC_SR & BV(SUPC_SR_OSCSEL)))
+ {
+ SUPC_CR = BV(SUPC_CR_XTALSEL) | SUPC_CR_KEY(0xA5);
+ while (!(SUPC_SR & BV(SUPC_SR_OSCSEL)));
+ }
+
+ // Initialize main oscillator
+ if (!(CKGR_MOR & BV(CKGR_MOR_MOSCSEL)))
+ {
+ CKGR_MOR = CKGR_MOR_KEY(0x37) | BOARD_OSC_COUNT | 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) | BOARD_OSC_COUNT | BV(CKGR_MOR_MOSCRCEN) | BV(CKGR_MOR_MOSCXTEN) | BV(CKGR_MOR_MOSCSEL);
+ timeout = CLOCK_TIMEOUT;
+ while (!(PMC_SR & BV(PMC_SR_MOSCSELS)) && --timeout);
+
+ PMC_MCKR = (PMC_MCKR & ~(uint32_t)PMC_MCKR_CSS_MASK) | PMC_MCKR_CSS_MAIN_CLK;
+ timeout = CLOCK_TIMEOUT;
+ while (!(PMC_SR & BV(PMC_SR_MCKRDY)) && --timeout);
+
+ // Initialize and enable PLL clock
+ CKGR_PLLR = evaluate_pll() | BV(CKGR_PLLR_STUCKTO1) | CKGR_PLLR_PLLCOUNT(0x1);
+ timeout = CLOCK_TIMEOUT;
+ while (!(PMC_SR & BV(PMC_SR_LOCK)) && --timeout);
- /* Master clock: select PLL clock and no prescaling */
- PMC_MCKR_R = PMC_MCKR_CSS_PLL_CLK;
+ PMC_MCKR = PMC_MCKR_CSS_MAIN_CLK;
+ timeout = CLOCK_TIMEOUT;
+ while (!(PMC_SR & BV(PMC_SR_MCKRDY)) && --timeout);
- CKGR_PLLR_R = evaluate_pll();
+ PMC_MCKR = PMC_MCKR_CSS_PLL_CLK;
+ timeout = CLOCK_TIMEOUT;
+ while (!(PMC_SR & BV(PMC_SR_MCKRDY)) && --timeout);
}