DSP2812例程BLDC3_1中speed模块是如何计算速度的？

#ifndef __SPEED_PR_H__
#define __SPEED_PR_H__

typedef struct {
       Uint32 NewTimeStamp;   // Variable : New 'Timestamp' corresponding to a capture event (Q0) - independently with global Q
       Uint32 OldTimeStamp;   // Variable : Old 'Timestamp' corresponding to a capture event (Q0) - independently with global Q
       Uint32 TimeStamp;      // Input : Current 'Timestamp' corresponding to a capture event (Q0) - independently with global Q
       Uint32 SpeedScaler;     // Parameter :  Scaler converting 1/N cycles to a GLOBAL_Q speed (Q0) - independently with global Q
       int32 EventPeriod;     // Input/Variable :  Event Period (Q0) - independently with global Q
       int16 InputSelect;       // Input : Input selection between TimeStamp (InputSelect=0) and EventPeriod (InputSelect=1)
       _iq Speed;              // Output :  speed in per-unit
       Uint32 BaseRpm;          // Parameter : Scaler converting GLOBAL_Q speed to rpm (Q0) speed - independently with global Q
       int32 SpeedRpm;         // Output : speed in r.p.m. (Q0) - independently with global Q
       void (*calc)();          // Pointer to the calulation function
       } SPEED_MEAS_CAP;        // Data type created

/*
Note that
         SpeedScaler = 60*f/rmp_max
where f = CLK_freq/(128*N), N = number of teeth in sprocket
and 128 is pre-determined prescaler of timer 2 (used by capture)
*/

typedef SPEED_MEAS_CAP *SPEED_MEAS_CAP_handle;
/*-----------------------------------------------------------------------------
Default initalizer for the SPEED_MEAS_CAP object.
-----------------------------------------------------------------------------*/                    
// SpeedScaler = 260 based on f(clk) 25 MHz, f(samping)= 16.67, 25 kHz
// rmp_max = 1800 rpm

#define SPEED_MEAS_CAP_DEFAULTS   { 0, \
                                    0, \
                                    0, \
                                   260, \
                                    0, \
                                    0, \
                                    0, \
                                   1800, \
                                    0, \
                                  (void (*)(Uint32))speed_prd_calc }

/*------------------------------------------------------------------------------
Prototypes for the functions in SPEED_PR.C
------------------------------------------------------------------------------*/
void speed_prd_calc(SPEED_MEAS_CAP_handle);

#endif // __SPEED_PR_H__

源文件如下：