Xtensa: Add implementation of system timer; Correct CFLAGS

arch/xtensa/src/esp32/esp32_timerisr.c

@@ -45,6 +45,7 @@
 
 #include <nuttx/arch.h>
 #include <arch/board/board.h>
+#include <arch/xtensa/xtensa_specregs.h>
 
 #include "clock/clock.h"
 #include "xtensa.h"
@@ -53,10 +54,81 @@
  * Pre-processor Definitions
  ****************************************************************************/
 
+#warning REVISIT .. Need XT_CLOCK_FREQ
+#define XT_CLOCK_FREQ       80000000
+
+/****************************************************************************
+ * Private data
+ ****************************************************************************/
+
+static uint32_t g_tick_divisor;
+
 /****************************************************************************
  * Private Functions
  ****************************************************************************/
 
+/****************************************************************************
+ * Function:  xtensa_getcount, xtensa_getcompare, xtensa_setcompare, and
+ *            xtensa_enable_timer
+ *
+ * Description:
+ *   Lower level operations on Xtensa special registers.
+ *
+ ****************************************************************************/
+
+/* Return the current value of the cyle count register */
+
+static inline uint32_t xtensa_getcount(void)
+{
+  uint32_t count;
+
+  __asm__ __volatile__
+  (
+    "rsr %0, CCOUNT"  : "=r"(count)
+  );
+
+  return count;
+}
+
+/* Return the old value of the compare register */
+
+static inline uint32_t xtensa_getcompare(void)
+{
+  uint32_t compare;
+
+  __asm__ __volatile__
+  (
+    "rsr %0, XT_CCOMPARE"  : "=r"(compare)
+  );
+
+  return compare;
+}
+
+/* Set the value of the compare register */
+
+static inline void xtensa_setps(uint32_t compare)
+{
+  __asm__ __volatile__
+  (
+    "wsr %0, XT_CCOMPARE"  : : "r"(compare)
+  );
+}
+
+/* Enable the timer interrupt.  NOTE: This is non-atomic but safe in this
+ * context because this occurs early in the initialization sequence.
+ */
+
+static inline void xtensa_enable_timer(void)
+{
+  __asm__ __volatile__
+  (
+    "rsr a2, INTENABLE"
+    "ori a2, XT_TIMER_INTEN"
+    "wsr a2, INTENABLE"
+    :  : "a2"
+  );
+}
+
 /****************************************************************************
  * Function:  esp32_timerisr
  *
@@ -64,14 +136,43 @@
  *   The timer ISR will perform a variety of services for various portions
  *   of the systems.
  *
+ *   Xtensa timers work by comparing a cycle counter with a preset value.
+ *   Once the match occurs an interrupt is generated, and the handler has to
+ *   set a new cycle count into the comparator.  To avoid clock drift due to
+ *   interrupt latency, the new cycle count is computed from the old, not the
+ *   time the interrupt was serviced. However if a timer interrupt is ever
+ *   serviced more than one tick late, it is necessary to process multiple
+ *   ticks until the new cycle count is in the future, otherwise the next
+ *   timer interrupt would not occur until after the cycle counter had
+ *   wrapped (2^32 cycles later).
+ *
  ****************************************************************************/
 
 static int esp32_timerisr(int irq, uint32_t *regs)
 {
-  /* Process timer interrupt */
+  uint32_t compare;
+  uint32_t diff;
 
-  sched_process_timer();
-  return 0;
+  do
+    {
+      /* Increment the compare register for the next tick */
+
+      compare = xtensa_getcompare();
+      xtensa_setcompare(count + g_tick_divisor);
+
+      /* Process one timer tick */
+
+      sched_process_timer();
+
+      /* Check if we are falling behind and need to process multiple timer
+       * interrupts.
+       */
+
+      diff = xtensa_readcount() - compare;
+    }
+  while (diff < divisor);
+
+  return OK;
 }
 
 /****************************************************************************
@@ -89,17 +190,34 @@ static int esp32_timerisr(int irq, uint32_t *regs)
 
 void xtensa_timer_initialize(void)
 {
-  uint32_t regval;
+  uint64_t divisor;
+  uint32_t count;
 
-  /* Configured the timer0 as the system timer */
-#warning Missing logic
+  /* Configured the timer0 as the system timer.
+   *
+   * divisor = XT_CLOCK_FREQ / ticks_per_sec
+   *         = XT_CLOCK_FREQ / (ticks_per_usec * 1000000)
+   *         = (1000000 * XT_CLOCK_FREQ) / ticks_per_usec
+   *
+   * A long long calculation is used to preserve accuracy in all cases.
+   */
+
+  divisor = (1000000ull * (uint64_t)XT_CLOCK_FREQ) / CONFIG_USEC_PER_TICK;
+  DEBUGASSERT(divisor <= UINT32_MAX)
+  g_tick_divisor = divisor;
+
+  /* Set up periodic timer */
+
+  count = xtensa_getcount();
+  xtensa_setcompare(count + divisor);
 
   /* Attach the timer interrupt vector */
 
   (void)irq_attach(XTENSA_IRQ_TIMER0, (xcpt_t)esp32_timerisr);
 
-  /* Enable SysTick interrupts */
-#warning Missing logic
+  /* Enable the timer interrupt at the device level */
+
+  xtensa_enable_timer();
 
   /* And enable the timer interrupt */
 

configs/esp32-core/nsh/Make.defs

@@ -78,8 +78,8 @@ ifneq ($(CONFIG_DEBUG_NOOPT),y)
   ARCHOPTIMIZATION += $(MAXOPTIMIZATION) -fno-strict-aliasing -fno-strength-reduce -fomit-frame-pointer
 endif
 
-ARCHCFLAGS = -fno-builtin
-ARCHCXXFLAGS = -fno-builtin -fno-exceptions -fcheck-new -fno-rtti
+ARCHCFLAGS = -fno-builtin -ffunction-sections -fdata-sections -fstrict-volatile-bitfields -mlongcalls -MMD -MP
+ARCHCXXFLAGS = $(ARCHCFLAGS) -fno-exceptions -fcheck-new -fno-rtti
 ARCHWARNINGS = -Wall -Wstrict-prototypes -Wshadow -Wundef
 ARCHWARNINGSXX = -Wall -Wshadow -Wundef
 ARCHDEFINES =