On Thu, 27 Aug 2015, Josh Koffman wrote:

> Hi Sergio,
>
> Thanks for the ideas. Just for reference, in xc8 you can enable and
> disable interrupts by using ei() and di() respectively.
>
> For my BAM code I'm hoping to do 8 channels at once, so I'll be
> preprocessing the current dimmer value of all channels to make a
> single variable that holds the state of all channels for any given
> time slice. Hopefully it works out!

In that case:


// assume all 8 channels are in a single port
#define BAM_PORT PORTA

// globals
unsigned char
 	bit_cnt, bit_mask, bit_pos, BAM_buff[8], chan_buff[8];


// BAM_buff[j] is the slice of chan_buff[][j]
// i.e. row[j] of BAM_buff consists of col[j] of chan_buff

// from what I've read, there is no advantage to storing
// chan_buff[][7] as BAM_buff[0] so using left shifts in the
// following code just makes things much more complicated for
// no added benefit

void init_BAM(void)
{
  	// disable interrupts
 	di();

  	bit_cnt   =3D 1;
  	bit_mask  =3D 0x80;
 	bit_pos   =3D 0;

 	for (j=3D0; j<8; j++)
 	{
 		BAM_buff[j] =3D 0;
 		chan_buff[j] =3D 0;
 	}

 	BAM_PORT =3D 0;

  	// enable interrupts
 	ei();
}


void set_channel_value(unsigned char indx, unsigned char val)
{
 	unsigned char
 		j, mask;


// note for this to work col[j] of chan_buff is rearranged in row[j] of BAM=
_buff

 	chan_buff[indx] =3D val;

 	mask =3D 1 << indx;

 	for (j=3D0; j<8; j++)
  	{
 		if ((val & 1) =3D=3D 0)
 		{
 			// bit j of chan_buff[indx] is 0 so
 			// clear the coressponding bit
 			BAM_buff[j] &=3D ~mask;
 		}
 		else
 		{
 			// bit j of chan_buff[indx] is 1 so
 			// set the coressponding bit
 			BAM_buff[j] |=3D mask;
 		}

 		val >>=3D 1;
  	}

  	// disable interrupts
 	di();

 	BAM_PORT =3D BAM_buff[bit_pos];

  	// enable interrupts
 	ei();
}


// this proc is called within the ISR

void service_BAM(void)
{
// this proc processes 8 channels in parallel
// each channel is only one bit wide
// the value of each channel is output serially one bit at a time
// the value of each channel takes 255 ticks to output competely

  	bit_cnt--;

  	if (bit_cnt =3D=3D 0)
  	{
 		// don't calculate bit_mask from bit_pos in the ISR as
 		// as variable shifts are expensive and unnecessary in
 		//  this case

  		if ((bit_mask & 0x80) =3D=3D 0)
  		{
  			bit_mask <<=3D 1;
 			bit_pos++;
  		}
  		else
  		{	bit_mask =3D 1;
 			bit_pos  =3D 0;
  		}

  		bit_cnt =3D bit_mask;

  		// I'm assuming the output pins are defined as a group at compile time

 		BAM_PORT =3D BAM_buff[bit_pos];
  	}
}


Regards
Sergio Masci
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