B166ER - Made in Cyberspace

CCS is a very nice compiler for PIC family of micro-controllers - the compiler includes a fair amount of built-in functions, many of which deal with bit manipulation - crucial functions when it comes to communications. Too bad I have to write these manually when porting communication to the NEC 78f9418 .

Having a 7 byte bitfield and transmitting it via low-speed PWM is not complex, and this is how the original code looked like, for PIC :

for (i = 0; i < 56; i++) {
shift_bit=shift_left (&irm, sizeof(ir_packet), 1);
send_bit(shift_bit);
}

Simple - 7 bytes are 56 bits, shift_left then accepts the address of irm, which is a structure of type ir_packet, shifted 1 bit to the left. The bit is then sent on it’s way.
Writing this code without the shift_left function proved to be somewhat fun though

packetBytePointer=&(BYTE *)&irm+6;
for(o=0;o<7;o++)
{
transmittedByte=*packetBytePointer;
for(z=0;z<8;z++)
{
send_bit(transmittedByte&0x80);
transmittedByte<<=1;
}
packetBytePointer--;

}

The above piece of code first puts an address to the last byte of the structure into a pointer, then assigns the value that is at that address to a temporary parameter of type BYTE (it's just an unsigned char) , and then simply iterates through it by shifting left and applying the 10000000 mask to it.
When the iteration is done, the address of the pointer is decreased to the begin the procedure on the next (previous memory-wise) byte.
This implementation was actually better in my case than shift_left of CCS , because it does not alter the original structure, so if you are storing your operational parameters in a structure that fits the transmission packet (common for simple devices such as “dumb” thermostats and motors), you don’t need to make another copy of the structure.

Bookmark to: