// license:BSD-3-Clause
// copyright-holders:Derrick Renaud, Couriersud
#include "emu.h"
#include "flt_rc.h"
// device type definition
DEFINE_DEVICE_TYPE(FILTER_RC, filter_rc_device, "filter_rc", "RC Filter")
//**************************************************************************
// LIVE DEVICE
//**************************************************************************
//-------------------------------------------------
// filter_rc_device - constructor
//-------------------------------------------------
filter_rc_device::filter_rc_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
: device_t(mconfig, FILTER_RC, tag, owner, clock),
device_sound_interface(mconfig, *this),
m_stream(nullptr),
m_k(0),
m_memory(0),
m_type(LOWPASS),
m_R1(1),
m_R2(1),
m_R3(1),
m_C(0)
{
}
//-------------------------------------------------
// device_start - device-specific startup
//-------------------------------------------------
void filter_rc_device::device_start()
{
m_stream = stream_alloc(1, 1, machine().sample_rate());
recalc();
save_item(NAME(m_k));
save_item(NAME(m_memory));
save_item(NAME(m_type));
save_item(NAME(m_R1));
save_item(NAME(m_R2));
save_item(NAME(m_R3));
save_item(NAME(m_C));
}
//-------------------------------------------------
// sound_stream_update - handle a stream update
//-------------------------------------------------
void filter_rc_device::sound_stream_update(sound_stream &stream, stream_sample_t **inputs, stream_sample_t **outputs, int samples)
{
stream_sample_t *src = inputs[0];
stream_sample_t *dst = outputs[0];
int memory = m_memory;
switch (m_type)
{
case LOWPASS:
while (samples--)
{
memory += ((*src++ - memory) * m_k) / 0x10000;
*dst++ = memory;
}
break;
case HIGHPASS:
case AC:
while (samples--)
{
*dst++ = *src - memory;
memory += ((*src++ - memory) * m_k) / 0x10000;
}
break;
}
m_memory = memory;
}
void filter_rc_device::recalc()
{
double Req;
switch (m_type)
{
case LOWPASS:
if (m_C == 0.0)
{
/* filter disabled */
m_k = 0x10000;
return;
}
Req = (m_R1 * (m_R2 + m_R3)) / (m_R1 + m_R2 + m_R3);
break;
case HIGHPASS:
case AC:
if (m_C == 0.0)
{
/* filter disabled */
m_k = 0x0;
m_memory = 0x0;
return;
}
Req = m_R1;
break;
default:
fatalerror("filter_rc_setRC: Wrong filter type %d\n", m_type);
}
/* Cut Frequency = 1/(2*Pi*Req*C) */
/* k = (1-(EXP(-TIMEDELTA/RC))) */
m_k = 0x10000 - 0x10000 * (exp(-1 / (Req * m_C) / machine().sample_rate()));
}