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46 lines
779 B
46 lines
779 B
15 years ago
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#include <avr/io.h>
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#include <stdint.h>
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#include <math.h>
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#include <spi.h>
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void spi_init(){
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uint8_t spcr, spsr, d;
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/* calculate clock divisor,
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* gcc with optimize will do that calculation compile-time. */
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uint8_t spi_clock_divisor(){
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double d;
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d = F_CPU / SPI_BAUDRATE;
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d = ceil((log(d)/log(2))*0.95); // clock needs dividing by 2^d
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// the 0.95 to avoid ceil issues
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return d-1; // the -1 because minimum divisor is /2
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}
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d = spi_clock_divisor();
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if(d>7){
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#warning "spi baudrate too slow, cannot be set"
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d=7;
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}
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spsr = 0;
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spsr |= (d & 1) ? 0 : _BV(SPI2X);
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spcr = 0 | _BV(SPIE) | _BV(SPE);
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spcr |= (d & 2) ? _BV(SPR0) : 0;
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spcr |= (d & 4) ? _BV(SPR1) : 0;
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#ifdef SPI_MASTER
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spcr |= _BV(MSTR);
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#endif
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SPCR = spcr;
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SPSR = spsr;
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}
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