Merge pull request #1065 from uknoblic/cc2538_speed

CC2538: Allow for configuration of processor clocks

cpu/cc2538/clock.c

@@ -37,12 +37,12 @@
  * Implementation of the clock module for the cc2538
  *
  * To implement the clock functionality, we use the SysTick peripheral on the
- * cortex-M3. We run the system clock at 16 MHz and we set the SysTick to give
- * us 128 interrupts / sec. However, the Sleep Timer counter value is used for
- * the number of elapsed ticks in order to avoid a significant time drift caused
- * by PM1/2. Contrary to the Sleep Timer, the SysTick peripheral is indeed
- * frozen during PM1/2, so adjusting upon wake-up a tick counter based on this
- * peripheral would hardly be accurate.
+ * cortex-M3. We run the system clock at a configurable speed and set the 
+ * SysTick to give us 128 interrupts / sec. However, the Sleep Timer counter 
+ * value is used for the number of elapsed ticks in order to avoid a 
+ * significant time drift caused by PM1/2. Contrary to the Sleep Timer, the 
+ * SysTick peripheral is indeed frozen during PM1/2, so adjusting upon wake-up 
+ * a tick counter based on this peripheral would hardly be accurate.
  * @{
  *
  * \file
@@ -62,7 +62,19 @@
 #include <stdint.h>
 /*---------------------------------------------------------------------------*/
 #define RTIMER_CLOCK_TICK_RATIO (RTIMER_SECOND / CLOCK_SECOND)
-#define RELOAD_VALUE (125000 - 1)  /** Fire 128 times / sec */
+
+/* Prescaler for GPT0:Timer A used for clock_delay_usec(). */
+#if SYS_CTRL_SYS_CLOCK < SYS_CTRL_1MHZ
+#error System clock speeds below 1MHz are not supported
+#endif
+#define PRESCALER_VALUE         (SYS_CTRL_SYS_CLOCK / SYS_CTRL_1MHZ - 1)
+
+/* Reload value for SysTick counter */
+#if SYS_CTRL_SYS_CLOCK % CLOCK_SECOND
+/* Too low clock speeds will lead to reduced accurracy */
+#error System clock speed too slow for CLOCK_SECOND, accuracy reduced
+#endif
+#define RELOAD_VALUE            (SYS_CTRL_SYS_CLOCK / CLOCK_SECOND - 1)
 
 static volatile uint64_t rt_ticks_startup = 0, rt_ticks_epoch = 0;
 /*---------------------------------------------------------------------------*/
@@ -74,8 +86,8 @@ static volatile uint64_t rt_ticks_startup = 0, rt_ticks_epoch = 0;
  *
  * We also initialise GPT0:Timer A, which is used by clock_delay_usec().
  * We use 16-bit range (individual), count-down, one-shot, no interrupts.
- * The system clock is at 16MHz giving us 62.5 nano sec ticks for Timer A.
- * Prescaled by 16 gives us a very convenient 1 tick per usec
+ * The prescaler is computed according to the system clock in order to get 1
+ * tick per usec.
  */
 void
 clock_init(void)
@@ -98,15 +110,14 @@ clock_init(void)
   /* Make sure GPT0 is off */
   REG(GPT_0_BASE + GPTIMER_CTL) = 0;
 
-
   /* 16-bit */
   REG(GPT_0_BASE + GPTIMER_CFG) = 0x04;
 
   /* One-Shot, Count Down, No Interrupts */
   REG(GPT_0_BASE + GPTIMER_TAMR) = GPTIMER_TAMR_TAMR_ONE_SHOT;
 
-  /* Prescale by 16 (thus, value 15 in TAPR) */
-  REG(GPT_0_BASE + GPTIMER_TAPR) = 0x0F;
+  /* Prescale depending on system clock used */
+  REG(GPT_0_BASE + GPTIMER_TAPR) = PRESCALER_VALUE;
 }
 /*---------------------------------------------------------------------------*/
 CCIF clock_time_t

cpu/cc2538/dev/i2c.c

@@ -43,15 +43,7 @@
 
 #include <stdint.h>
 #include "clock.h"
-/*---------------------------------------------------------------------------*/
-/* Additional functions */
-static uint32_t
-get_sys_clock(void)
-{
-  /* Get the clock status diviser */
-  return SYS_CTRL_32MHZ /
-         (1 << (REG(SYS_CTRL_CLOCK_STA) & SYS_CTRL_CLOCK_STA_SYS_DIV));
-}
+#include "sys-ctrl.h"
 /*---------------------------------------------------------------------------*/
 void
 i2c_init(uint8_t port_sda, uint8_t pin_sda, uint8_t port_scl, uint8_t pin_scl,
@@ -111,7 +103,7 @@ void
 i2c_set_frequency(uint32_t freq)
 {
   /* Peripheral clock setting, using the system clock */
-  REG(I2CM_TPR) = ((get_sys_clock() + (2 * 10 * freq) - 1) /
+  REG(I2CM_TPR) = ((SYS_CTRL_SYS_CLOCK + (2 * 10 * freq) - 1) /
                    (2 * 10 * freq)) - 1;
 }
 /*---------------------------------------------------------------------------*/

cpu/cc2538/dev/spi.c

@@ -226,8 +226,8 @@ spix_init(uint8_t spi)
   /* Start by disabling the peripheral before configuring it */
   REG(regs->base + SSI_CR1) = 0;
 
-  /* Set the IO clock as the SSI clock */
-  REG(regs->base + SSI_CC) = 1;
+  /* Set the system clock as the SSI clock */
+  REG(regs->base + SSI_CC) = 0;
 
   /* Set the mux correctly to connect the SSI pins to the correct GPIO pins */
   ioc_set_sel(regs->clk.port,

cpu/cc2538/dev/sys-ctrl.c

@@ -70,17 +70,18 @@ sys_ctrl_init()
    * 32KHz source: RC or crystal, according to SYS_CTRL_OSC32K_USE_XTAL
    * System Clock: 32 MHz
    * Power Down Unused
-   * I/O Div: 16MHz
-   * Sys Div: 16MHz
+   * I/O Div: according to SYS_CTRL_IO_DIV
+   * Sys Div: according to SYS_CTRL_SYS_DIV
    * Rest: Don't care
    */
 
   val = SYS_CTRL_OSCS | SYS_CTRL_CLOCK_CTRL_OSC_PD
-      | SYS_CTRL_CLOCK_CTRL_IO_DIV_16MHZ | SYS_CTRL_CLOCK_CTRL_SYS_DIV_16MHZ;
+    | SYS_CTRL_IO_DIV | SYS_CTRL_SYS_DIV;
   REG(SYS_CTRL_CLOCK_CTRL) = val;
 
-  while((REG(SYS_CTRL_CLOCK_STA) & (SYS_CTRL_CLOCK_STA_OSC32K |
-        SYS_CTRL_CLOCK_STA_OSC)) != SYS_CTRL_OSCS);
+  while((REG(SYS_CTRL_CLOCK_STA) 
+        & (SYS_CTRL_CLOCK_STA_OSC32K | SYS_CTRL_CLOCK_STA_OSC)) 
+        != SYS_CTRL_OSCS);
 
 #if SYS_CTRL_OSC32K_USE_XTAL
   /* Wait for the 32-kHz crystal oscillator to stabilize */
@@ -94,7 +95,20 @@ sys_ctrl_reset()
 {
   REG(SYS_CTRL_PWRDBG) = SYS_CTRL_PWRDBG_FORCE_WARM_RESET;
 }
-
+/*---------------------------------------------------------------------------*/
+uint32_t
+sys_ctrl_get_sys_clock(void)
+{
+  return SYS_CTRL_32MHZ >> (REG(SYS_CTRL_CLOCK_STA) &
+                            SYS_CTRL_CLOCK_STA_SYS_DIV);
+}
+/*---------------------------------------------------------------------------*/
+uint32_t
+sys_ctrl_get_io_clock(void)
+{
+  return SYS_CTRL_32MHZ >> ((REG(SYS_CTRL_CLOCK_STA) &
+                             SYS_CTRL_CLOCK_STA_IO_DIV) >> 8);
+}
 /**
  * @}
  * @}

cpu/cc2538/dev/sys-ctrl.h

@@ -42,6 +42,8 @@
  */
 #ifndef SYS_CTRL_H_
 #define SYS_CTRL_H_
+
+#include <stdint.h>
 /*---------------------------------------------------------------------------*/
 /** \name SysCtrl Constants, used by the SYS_DIV and IO_DIV bits of the
  * SYS_CTRL_CLOCK_CTRL register
@@ -242,6 +244,33 @@
 #endif
 /** @} */
 /*---------------------------------------------------------------------------*/
+/** \name System clock divisor selection
+ * @{
+ */
+#ifdef SYS_CTRL_CONF_SYS_DIV
+#if SYS_CTRL_CONF_SYS_DIV & ~SYS_CTRL_CLOCK_CTRL_SYS_DIV
+#error Invalid system clock divisor
+#endif
+#define SYS_CTRL_SYS_DIV        SYS_CTRL_CONF_SYS_DIV
+#else
+#define SYS_CTRL_SYS_DIV        SYS_CTRL_CLOCK_CTRL_SYS_DIV_16MHZ
+#endif
+
+#ifdef SYS_CTRL_CONF_IO_DIV
+#if SYS_CTRL_CONF_IO_DIV & ~SYS_CTRL_CLOCK_CTRL_IO_DIV
+#error Invalid I/O clock divisor
+#endif
+#define SYS_CTRL_IO_DIV         SYS_CTRL_CONF_IO_DIV
+#else
+#define SYS_CTRL_IO_DIV         SYS_CTRL_CLOCK_CTRL_IO_DIV_16MHZ
+#endif
+
+/* Returns actual system clock in Hz */
+#define SYS_CTRL_SYS_CLOCK      (SYS_CTRL_32MHZ >> SYS_CTRL_SYS_DIV)
+/* Returns actual I/O clock in Hz */
+#define SYS_CTRL_IO_CLOCK       (SYS_CTRL_32MHZ >> (SYS_CTRL_IO_DIV >> 8))
+/** @} */
+/*---------------------------------------------------------------------------*/
 /** \name SysCtrl functions
  * @{
  */
@@ -253,6 +282,12 @@ void sys_ctrl_init();
 /** \brief Generates a warm reset through the SYS_CTRL_PWRDBG register */
 void sys_ctrl_reset();
 
+/** \brief Returns the actual system clock in Hz */
+uint32_t sys_ctrl_get_sys_clock();
+
+/** \brief Returns the actual io clock in Hz */
+uint32_t sys_ctrl_get_io_clock();
+
 /** @} */
 
 #endif /* SYS_CTRL_H_ */

cpu/cc2538/dev/uart.c

@@ -136,7 +136,7 @@
  * Baud rate defines used in uart_init() to set the values of UART_IBRD and
  * UART_FBRD in order to achieve the configured baud rates.
  */
-#define UART_CLOCK_RATE       16000000 /* 16 MHz */
+#define UART_CLOCK_RATE       SYS_CTRL_SYS_CLOCK
 #define UART_CTL_HSE_VALUE    0
 #define UART_CTL_VALUE        (UART_CTL_RXE | UART_CTL_TXE | (UART_CTL_HSE_VALUE << 5))
 

cpu/cc2538/lpm.c

@@ -78,8 +78,8 @@ static unsigned long irq_energest = 0;
 #if LPM_CONF_STATS
 rtimer_clock_t lpm_stats[3];
 
-#define LPM_STATS_INIT()         do { memset(lpm_stats, 0, sizeof(lpm_stats)); \
-  } while(0)
+#define LPM_STATS_INIT() \
+  do { memset(lpm_stats, 0, sizeof(lpm_stats)); } while(0)
 #define LPM_STATS_ADD(pm, val)   do { lpm_stats[pm] += val; } while(0)
 #else
 #define LPM_STATS_INIT()
@@ -154,7 +154,7 @@ enter_pm0(void)
 static void
 select_32_mhz_xosc(void)
 {
-  /*First, make sure there is no ongoing clock source change */
+  /* First, make sure there is no ongoing clock source change */
   while((REG(SYS_CTRL_CLOCK_STA) & SYS_CTRL_CLOCK_STA_SOURCE_CHANGE) != 0);
 
   /* Turn on the 32 MHz XOSC and source the system clock on it. */
@@ -163,8 +163,15 @@ select_32_mhz_xosc(void)
   /* Wait for the switch to take place */
   while((REG(SYS_CTRL_CLOCK_STA) & SYS_CTRL_CLOCK_STA_OSC) != 0);
 
-  /* Power down the unused oscillator. */
-  REG(SYS_CTRL_CLOCK_CTRL) |= SYS_CTRL_CLOCK_CTRL_OSC_PD;
+  /* Power down the unused oscillator and restore divisors (silicon errata) */
+  REG(SYS_CTRL_CLOCK_CTRL) = (REG(SYS_CTRL_CLOCK_CTRL)
+#if SYS_CTRL_SYS_DIV == SYS_CTRL_CLOCK_CTRL_SYS_DIV_32MHZ
+    & ~SYS_CTRL_CLOCK_CTRL_SYS_DIV
+#endif
+#if SYS_CTRL_IO_DIV == SYS_CTRL_CLOCK_CTRL_IO_DIV_32MHZ
+    & ~SYS_CTRL_CLOCK_CTRL_IO_DIV
+#endif
+    ) | SYS_CTRL_CLOCK_CTRL_OSC_PD;
 }
 /*---------------------------------------------------------------------------*/
 static void
@@ -172,9 +179,19 @@ select_16_mhz_rcosc(void)
 {
   /*
    * Power up both oscillators in order to speed up the transition to the 32-MHz
-   * XOSC after wake up.
+   * XOSC after wake up. In addition, consider CC2538 silicon errata:
+   * "Possible Incorrect Value of Clock Dividers after PM2 and PM3" and
+   * set system clock divisor / I/O clock divisor to 16 MHz in case they run
+   * at full speed (=32 MHz)
    */
-  REG(SYS_CTRL_CLOCK_CTRL) &= ~SYS_CTRL_CLOCK_CTRL_OSC_PD;
+  REG(SYS_CTRL_CLOCK_CTRL) = (REG(SYS_CTRL_CLOCK_CTRL)
+#if SYS_CTRL_SYS_DIV == SYS_CTRL_CLOCK_CTRL_SYS_DIV_32MHZ
+    | SYS_CTRL_CLOCK_CTRL_SYS_DIV_16MHZ
+#endif
+#if SYS_CTRL_IO_DIV == SYS_CTRL_CLOCK_CTRL_IO_DIV_32MHZ
+    | SYS_CTRL_CLOCK_CTRL_IO_DIV_16MHZ
+#endif
+    ) & ~SYS_CTRL_CLOCK_CTRL_OSC_PD;
 
   /*First, make sure there is no ongoing clock source change */
   while((REG(SYS_CTRL_CLOCK_STA) & SYS_CTRL_CLOCK_STA_SOURCE_CHANGE) != 0);