71 lines
2.0 KiB
C
71 lines
2.0 KiB
C
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//-------------------------------------------------------------------------
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//-------------------------------------------------------------------------
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extern void PUT32 ( unsigned int, unsigned int );
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extern unsigned int GET32 ( unsigned int );
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extern void dummy ( unsigned int );
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#define ARM_TIMER_LOD 0x2000B400
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#define ARM_TIMER_VAL 0x2000B404
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#define ARM_TIMER_CTL 0x2000B408
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#define ARM_TIMER_DIV 0x2000B41C
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#define ARM_TIMER_CNT 0x2000B420
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#define SYSTIMERCLO 0x20003004
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#define GPFSEL1 0x20200004
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#define GPSET0 0x2020001C
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#define GPCLR0 0x20200028
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//From experiments and from the manual the freerunning ARM timer is
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//not affected by the timer enable bit. Not affected by the 0x41C
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//prescaler. Not affected by bits 3:2 of the control register.
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//And is affected by bits 23:16 of the control register.
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//It still appears as if the system timer is 250Mhz as mentioned somewhere
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//in the manual (starts up at 250MHz).
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//If we divide 250MHz/250 we can make the free running clock 1mhz
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//wait for 4 million ticks and the led will change state every 4 seconds
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//Note the free running timer is an up counting timer, the other arm
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//timer is a down counter.
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#define TIMEOUT 4000000
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//-------------------------------------------------------------------------
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int notmain ( void )
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{
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unsigned int ra;
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unsigned int rb;
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ra=GET32(GPFSEL1);
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ra&=~(7<<18);
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ra|=1<<18;
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PUT32(GPFSEL1,ra);
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PUT32(ARM_TIMER_CTL,0x00F90000);
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PUT32(ARM_TIMER_CTL,0x00F90200);
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rb=GET32(ARM_TIMER_CNT);
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while(1)
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{
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PUT32(GPSET0,1<<16);
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while(1)
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{
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ra=GET32(ARM_TIMER_CNT);
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if((ra-rb)>=TIMEOUT) break;
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}
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rb+=TIMEOUT;
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PUT32(GPCLR0,1<<16);
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while(1)
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{
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ra=GET32(ARM_TIMER_CNT);
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if((ra-rb)>=TIMEOUT) break;
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}
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rb+=TIMEOUT;
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}
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return(0);
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}
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//-------------------------------------------------------------------------
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//-------------------------------------------------------------------------
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