esp-idf/components/freertos/include/freertos/xtensa_timer.h

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        XTENSA INFORMATION FOR RTOS TICK TIMER AND CLOCK FREQUENCY

This header contains definitions and macros for use primarily by Xtensa
RTOS assembly coded source files. It includes and uses the Xtensa hardware
abstraction layer (HAL) to deal with config specifics. It may also be
included in C source files.

User may edit to modify timer selection and to specify clock frequency and
tick duration to match timer interrupt to the real-time tick duration.

If the RTOS has no timer interrupt, then there is no tick timer and the
clock frequency is irrelevant, so all of these macros are left undefined
and the Xtensa core configuration need not have a timer.

*******************************************************************************/

#ifndef XTENSA_TIMER_H
#define XTENSA_TIMER_H

#ifdef __ASSEMBLER__
#include    <xtensa/coreasm.h>
#endif

#include    <xtensa/corebits.h>
#include    <xtensa/config/system.h>

#include    "xtensa_rtos.h"     /* in case this wasn't included directly */

#include    "FreeRTOSConfig.h"

/*
Select timer to use for periodic tick, and determine its interrupt number 
and priority. User may specify a timer by defining XT_TIMER_INDEX with -D,
in which case its validity is checked (it must exist in this core and must 
not be on a high priority interrupt - an error will be reported in invalid).
Otherwise select the first low or medium priority interrupt timer available.
*/
#if XCHAL_NUM_TIMERS == 0

  #error "This Xtensa configuration is unsupported, it has no timers."

#else

#ifndef XT_TIMER_INDEX
  #if XCHAL_TIMER3_INTERRUPT != XTHAL_TIMER_UNCONFIGURED
    #if XCHAL_INT_LEVEL(XCHAL_TIMER3_INTERRUPT) <= XCHAL_EXCM_LEVEL
      #undef  XT_TIMER_INDEX
      #define XT_TIMER_INDEX    3
    #endif
  #endif
  #if XCHAL_TIMER2_INTERRUPT != XTHAL_TIMER_UNCONFIGURED
    #if XCHAL_INT_LEVEL(XCHAL_TIMER2_INTERRUPT) <= XCHAL_EXCM_LEVEL
      #undef  XT_TIMER_INDEX
      #define XT_TIMER_INDEX    2
    #endif
  #endif
  #if XCHAL_TIMER1_INTERRUPT != XTHAL_TIMER_UNCONFIGURED
    #if XCHAL_INT_LEVEL(XCHAL_TIMER1_INTERRUPT) <= XCHAL_EXCM_LEVEL
      #undef  XT_TIMER_INDEX
      #define XT_TIMER_INDEX    1
    #endif
  #endif
  #if XCHAL_TIMER0_INTERRUPT != XTHAL_TIMER_UNCONFIGURED
    #if XCHAL_INT_LEVEL(XCHAL_TIMER0_INTERRUPT) <= XCHAL_EXCM_LEVEL
      #undef  XT_TIMER_INDEX
      #define XT_TIMER_INDEX    0
    #endif
  #endif
#endif
#ifndef XT_TIMER_INDEX
  #error "There is no suitable timer in this Xtensa configuration."
#endif

#define XT_CCOMPARE             (CCOMPARE + XT_TIMER_INDEX)
#define XT_TIMER_INTNUM         XCHAL_TIMER_INTERRUPT(XT_TIMER_INDEX)
#define XT_TIMER_INTPRI         XCHAL_INT_LEVEL(XT_TIMER_INTNUM)
#define XT_TIMER_INTEN          (1 << XT_TIMER_INTNUM)

#if XT_TIMER_INTNUM == XTHAL_TIMER_UNCONFIGURED
  #error "The timer selected by XT_TIMER_INDEX does not exist in this core."
#elif XT_TIMER_INTPRI > XCHAL_EXCM_LEVEL
  #error "The timer interrupt cannot be high priority (use medium or low)."
#endif

#endif /* XCHAL_NUM_TIMERS */

/*
Set processor clock frequency, used to determine clock divisor for timer tick.
User should BE SURE TO ADJUST THIS for the Xtensa platform being used.
If using a supported board via the board-independent API defined in xtbsp.h,
this may be left undefined and frequency and tick divisor will be computed 
and cached during run-time initialization.

NOTE ON SIMULATOR:
Under the Xtensa instruction set simulator, the frequency can only be estimated 
because it depends on the speed of the host and the version of the simulator.
Also because it runs much slower than hardware, it is not possible to achieve
real-time performance for most applications under the simulator. A frequency
too low does not allow enough time between timer interrupts, starving threads.
To obtain a more convenient but non-real-time tick duration on the simulator, 
compile with xt-xcc option "-DXT_SIMULATOR".
Adjust this frequency to taste (it's not real-time anyway!).
*/
#if defined(XT_SIMULATOR) && !defined(XT_CLOCK_FREQ)
#define XT_CLOCK_FREQ       configCPU_CLOCK_HZ
#endif

#if !defined(XT_CLOCK_FREQ) && !defined(XT_BOARD)
  #error "XT_CLOCK_FREQ must be defined for the target platform."
#endif

/*
Default number of timer "ticks" per second (default 100 for 10ms tick).
RTOS may define this in its own way (if applicable) in xtensa_rtos.h.
User may redefine this to an optimal value for the application, either by
editing this here or in xtensa_rtos.h, or compiling with xt-xcc option
"-DXT_TICK_PER_SEC=<value>" where <value> is a suitable number.
*/
#ifndef XT_TICK_PER_SEC
#define XT_TICK_PER_SEC    configTICK_RATE_HZ        /* 10 ms tick = 100 ticks per second */
#endif

/*
Derivation of clock divisor for timer tick and interrupt (one per tick).
*/
#ifdef XT_CLOCK_FREQ
#define XT_TICK_DIVISOR     (XT_CLOCK_FREQ / XT_TICK_PER_SEC)
#endif

#ifndef __ASSEMBLER__
extern unsigned _xt_tick_divisor;
extern void     _xt_tick_divisor_init(void);
#endif

#endif  /* XTENSA_TIMER_H */