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Annotation of xinu/h/clock.h, revision 1.1

1.1     ! root        1: /* clock.h--format of memory mapped registers for timer part of 68230 PI/T */
        !             2: 
        !             3: struct timercsr {
        !             4:   unsigned char tcsr;          /* timer control reg */
        !             5:   char dummy1; 
        !             6:   unsigned char tivr;          /* timer interrupt vector addr */
        !             7:   char dummy2;
        !             8:   unsigned char cpr_null;      /* r/w but noop 4th byte for cpr */
        !             9:   char dummy3;
        !            10:   unsigned char cpr_high;      /* high byte of counter preload reg */
        !            11:   char dummy4;
        !            12:   unsigned char cpr_med;       /* middle byte of counter preload reg */
        !            13:   char dummy5;
        !            14:   unsigned char cpr_low;       /* low byte of counter preload reg */
        !            15:   char dummy6;
        !            16:   unsigned char cnt_null;      /* r/w but noop 4th byte for counter reg */
        !            17:   char dummy7;
        !            18:   unsigned char cnt_high;      /* high byte, counter--read with clock off */
        !            19:   char dummy8;
        !            20:   unsigned char cnt_med;       /* mid. byte, counter--read with clock off */
        !            21:   char dummy9;
        !            22:   unsigned char cnt_low;       /* low byte, counter--read with clock off */
        !            23:   char dummy10;
        !            24:   unsigned char tstat;         /* bit 0 is zero-detect, rest read as 0 */
        !            25:                                /* write 1 to this byte to acknowledge tick */
        !            26: };
        !            27: 
        !            28: /* the memory-mapped location of timer registers, determined by digital */
        !            29: /* logic wired onto the mecb--(would be at higher adddress on bigger sys) */
        !            30: #define TIMER ((struct timercsr *)0x10021)
        !            31: 
        !            32: /* bit defs for tcr (timer control register)-- */
        !            33: #define CLOCKIE (5<<5)         /* user vectoring, int enabled */
        !            34: #define CLOCKDE (4<<5)         /* user vectoring, int disabled */
        !            35: #define LOADFROMCPR (0<<4)     /* when count hits 0 */
        !            36: #define LETROLLOVER (1<<4)     /* don't use CPR, just let it roll over */
        !            37: #define PRESCALE32 (0<<1)      /* count every 32 clock cycles */
        !            38:                                /* 1<<1 thru 3<<2 all involve a */
        !            39:                                /* pin on port C, for external clocking */
        !            40: #define CLOCKON (1<<0)         /* clock running */
        !            41: #define CLOCKOFF (0<<0)                /* clock not running */
        !            42: 
        !            43: /* Note: since PRESCALE32 is the only internal-only setting for bits 1-2, */
        !            44: /* we have as a result a timer downcounting every 32 cycles of the 4 Mhz  */
        !            45: /* crystal, i.e, 8 usecs/downcount, or 125,000 downcounts/second          */
        !            46: 

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