Pololu Orangutan X2 User Manual

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{

__asm__ volatile (

"1: push r22" "\n\t"

" ldi r22, 4" "\n\t"

"2: dec r22" "\n\t"

" brne 2b" "\n\t"

" pop r22" "\n\t"

" sbiw %0, 1" "\n\t"

" brne 1b"

: "=w" ( microseconds )

: "0" ( microseconds )

);

}

unsigned char SPIReceive( unsigned char data ) // data is often a junk byte (e.g. 0)

{

if ( SPITransmitting )

while ( ! ( SPSR & ( 1 << SPIF ))) // wait for completion of

; // previous transmission

delay_us( 3 ); // give the mega168 time to prepare

// return data

SPDR = data; // start bidirectional transfer

while ( ! ( SPSR & ( 1 << SPIF ))) // wait for completion of

; // transaction

// reading SPCR and SPDR will clear SPIF, so we will use our global flag

// to indicate that this does not mean we are currently transmitting

SPITransmitting = 0;

return SPDR;

}

We can now put wrapper functions around these low-level SPI commands to communicate with the mega168. For
instance, here is a command for setting motor 1:

void setMotor1( int speed )

{

// first, we'll prepare our command byte

unsigned char command;

if ( speed > 255 )

speed = 255;

if ( speed < -255 )

speed = -255;

if ( speed >= 0 )

command = 136; // motor 1, forward

else

{

command = 138; // motor 1, reverse

speed = -speed;

}

// the MSB of the speed gets tacked onto the command byte

command |= ( (unsigned char) speed & 0x80 ) >> 7;

// now, send the command

SPITransmit( command );

SPITransmit( (unsigned char) speed & 0x7F );

}

Orangutan X2 Command Documentation v1.01

2. ATmega644 SPI Configuration

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