void dss_lfsr_step(struct node_description *node)
{
const struct discrete_lfsr_desc *lfsr_desc = node->custom;
struct dss_lfsr_context *context = node->context;
PRECISION shiftAmount;
int fb0,fb1,fbresult,i;
/* Reset everything if necessary */
if((node->input[1] ? 1 : 0) == ((lfsr_desc->flags & DISC_LFSR_FLAG_RESET_TYPE_H) ? 1 : 0))
{
dss_lfsr_reset(node);
}
i=0;
/* Calculate the number of full shift register cycles since last machine sample. */
shiftAmount = ((context->sampleStep + context->t) / context->shiftStep);
context->t = (shiftAmount - (int)shiftAmount) * context->shiftStep; /* left over amount of time */
while(i<(int)shiftAmount)
{
i++;
/* Now clock the LFSR by 1 cycle and output */
/* Fetch the last feedback result */
fbresult=((context->lfsr_reg)>>(lfsr_desc->bitlength))&0x01;
/* Stage 2 feedback combine fbresultNew with infeed bit */
fbresult=dss_lfsr_function(lfsr_desc->feedback_function1,fbresult,((node->input[4])?0x01:0x00),0x01);
/* Stage 3 first we setup where the bit is going to be shifted into */
fbresult=fbresult*lfsr_desc->feedback_function2_mask;
/* Then we left shift the register, */
context->lfsr_reg=(context->lfsr_reg)<<1;
/* Now move the fbresult into the shift register and mask it to the bitlength */
context->lfsr_reg=dss_lfsr_function(lfsr_desc->feedback_function2,fbresult, (context->lfsr_reg), ((1<<(lfsr_desc->bitlength))-1));
/* Now get and store the new feedback result */
/* Fetch the feedback bits */
fb0=((context->lfsr_reg)>>(lfsr_desc->feedback_bitsel0))&0x01;
fb1=((context->lfsr_reg)>>(lfsr_desc->feedback_bitsel1))&0x01;
/* Now do the combo on them */
fbresult=dss_lfsr_function(lfsr_desc->feedback_function0,fb0,fb1,0x01);
context->lfsr_reg=dss_lfsr_function(DISC_LFSR_REPLACE,(context->lfsr_reg), fbresult<<(lfsr_desc->bitlength), ((2<<(lfsr_desc->bitlength))-1));
/* Now select the output bit */
node->output=((context->lfsr_reg)>>(lfsr_desc->output_bit))&0x01;
/* Final inversion if required */
if(lfsr_desc->flags & DISC_LFSR_FLAG_OUT_INVERT) node->output=(node->output)?0.0:1.0;
/* Gain stage */
node->output=(node->output)?(node->input[3])/2:-(node->input[3])/2;
/* Bias input as required */
node->output=node->output+node->input[5];
}
if(!node->input[0])
{
node->output=0;
}
}
int dss_lfsr_init(struct node_description *node)
{
struct dss_lfsr_context *context;
discrete_log("dss_lfsr_init() - Creating node %d.",node->node-NODE_00);
/* Allocate memory for the context array and the node execution order array */
if((node->context=malloc(sizeof(struct dss_lfsr_context)))==NULL)
{
discrete_log("dss_lfsr_init() - Failed to allocate local context memory.");
return 1;
}
else
{
/* Initialise memory */
memset(node->context,0,sizeof(struct dss_lfsr_context));
}
/* Initialise the object */
context=(struct dss_lfsr_context*)node->context;
context->sampleStep = 1.0 / Machine->sample_rate;
context->shiftStep = 1.0 / node->input[2];
context->t = 0;
dss_lfsr_reset(node);
return 0;
}
void dss_lfsr_step(struct node_description *node)
{
const struct discrete_lfsr_desc *lfsr_desc = node->custom;
struct dss_lfsr_context *context = node->context;
double cycles;
int clock, inc = 0;
int fb0,fb1,fbresult;
if (lfsr_desc->clock_type == DISC_CLK_IS_FREQ)
{
/* We need to keep clocking the internal clock even if disabled. */
cycles = (context->t_left + discrete_current_context->sample_time) / context->t_clock;
inc = (int)cycles;
context->t_left = (cycles - inc) * context->t_clock;
}
/* Reset everything if necessary */
if((DSS_LFSR_NOISE__RESET ? 1 : 0) == ((lfsr_desc->flags & DISC_LFSR_FLAG_RESET_TYPE_H) ? 1 : 0))
{
dss_lfsr_reset(node);
return;
}
switch (lfsr_desc->clock_type)
{
case DISC_CLK_ON_F_EDGE:
case DISC_CLK_ON_R_EDGE:
/* See if the clock has toggled to the proper edge */
clock = (DSS_LFSR_NOISE__CLOCK != 0);
if (context->last != clock)
{
context->last = clock;
if (lfsr_desc->clock_type == clock)
{
/* Toggled */
inc = 1;
}
}
break;
case DISC_CLK_BY_COUNT:
/* Clock number of times specified. */
inc = (int)DSS_LFSR_NOISE__CLOCK;
break;
}
for (clock = 0; clock < inc; clock++)
{
/* Fetch the last feedback result */
fbresult=((context->lfsr_reg)>>(lfsr_desc->bitlength))&0x01;
/* Stage 2 feedback combine fbresultNew with infeed bit */
fbresult=dss_lfsr_function(lfsr_desc->feedback_function1,fbresult,((DSS_LFSR_NOISE__FEED)?0x01:0x00),0x01);
/* Stage 3 first we setup where the bit is going to be shifted into */
fbresult=fbresult*lfsr_desc->feedback_function2_mask;
/* Then we left shift the register, */
context->lfsr_reg=(context->lfsr_reg)<<1;
/* Now move the fbresult into the shift register and mask it to the bitlength */
context->lfsr_reg=dss_lfsr_function(lfsr_desc->feedback_function2,fbresult, (context->lfsr_reg), ((1<<(lfsr_desc->bitlength))-1));
/* Now get and store the new feedback result */
/* Fetch the feedback bits */
fb0=((context->lfsr_reg)>>(lfsr_desc->feedback_bitsel0))&0x01;
fb1=((context->lfsr_reg)>>(lfsr_desc->feedback_bitsel1))&0x01;
/* Now do the combo on them */
fbresult=dss_lfsr_function(lfsr_desc->feedback_function0,fb0,fb1,0x01);
context->lfsr_reg=dss_lfsr_function(DISC_LFSR_REPLACE,(context->lfsr_reg), fbresult<<(lfsr_desc->bitlength), ((2<<(lfsr_desc->bitlength))-1));
/* Now select the output bit */
node->output=((context->lfsr_reg)>>(lfsr_desc->output_bit))&0x01;
/* Final inversion if required */
if(lfsr_desc->flags & DISC_LFSR_FLAG_OUT_INVERT) node->output=(node->output)?0.0:1.0;
/* Gain stage */
node->output=(node->output)?(DSS_LFSR_NOISE__AMP)/2:-(DSS_LFSR_NOISE__AMP)/2;
/* Bias input as required */
node->output=node->output+DSS_LFSR_NOISE__BIAS;
}
if(!DSS_LFSR_NOISE__ENABLE)
{
node->output=0;
}
}
