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Fixed period for both sn76489 and sn76489A periodic noise; fixes pitch in 'smooth criminal' demo for colecovision and fixes pitch (but not the waveform, which will require more work) of music in dorunrun; More work is required before the code will be bit accurate due to the way the real LFSR and periodic generator work. [Lord Nightmare, Kold666, PlgDavid]

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This commit is contained in:
Jonathan Gevaryahu 2010-01-15 21:31:39 +00:00
parent b998026736
commit 4b257e2c66
1 changed files with 16 additions and 7 deletions
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23
src/emu/sound/sn76496.c
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@ -16,9 +16,9 @@
** SN76489 uses a 15-bit shift register with taps on bits D and E, output on E,
XOR function; SN94624 is identical to SN76489.
It uses a 15-bit ring buffer for periodic noise/arbitrary duty cycle.
** SN76489A uses a 16-bit shift register with taps on bits D and E, output on F,
** SN76489A uses a 15-bit shift register with taps on bits D and E, output on F,
XNOR function
It uses a 16-bit ring buffer for periodic noise/arbitrary duty cycle.
It uses a 15-bit ring buffer for periodic noise/arbitrary duty cycle.
** SN76494 and SN76496 are PROBABLY identical in operation to the SN76489A
They have an audio input line which is mixed with the 4 channels of output.
** Sega Master System III/MD/Genesis PSG uses a 16-bit shift register with taps
@ -70,6 +70,11 @@
based on testing. Got rid of R->OldNoise and fixed taps accordingly.
Added stereo support for game gear.
11/15/2010 : Lord Nightmare
Fix an issue with SN76489 and SN76489A having the wrong periodic noise periods.
Note that properly emulating the noise cycle bit timing accurately may require
extensive rewriting.
TODO: * Implement the TMS9919 which is an earlier version, possibly
lacking the /8 clock divider, of the SN76489, and hence would
have a max clock of 500Khz and 4 clocks per sample, as opposed to
@ -79,6 +84,10 @@
* Test the NCR7496; Smspower says the whitenoise taps are A and E,
but this needs verification on real hardware.
* Factor out common code so that the SAA1099 can share some code.
* Implement periodic noise as using a pointer to a table rather than a
self feeding lfsr. Kold666's recording of dorunrun proves this is the
right way.
* Fix the whitenoise bit timing so that dorunrun matches Kold666's PCB sample.
***************************************************************************/
#include "emu.h"
@ -403,27 +412,27 @@ static void generic_start(const device_config *device, int feedbackmask, int noi
static DEVICE_START( sn76489 )
{
generic_start(device, 0x8000, 0x06, FALSE, FALSE, FALSE); // todo: verify; assumed to be the same as sn94624
generic_start(device, 0x4000, 0x03, FALSE, FALSE, FALSE); // todo: verify; assumed to be the same as sn94624
}
static DEVICE_START( sn76489a )
{
generic_start(device, 0x10000, 0x0C, TRUE, FALSE, FALSE); // verified by plgdavid
generic_start(device, 0x4000, 0x03, TRUE, FALSE, FALSE); // verified by plgdavid
}
static DEVICE_START( sn76494 )
{
generic_start(device, 0x10000, 0x0C, TRUE, FALSE, FALSE); // todo: verify; assumed to be the same as sn76489a
generic_start(device, 0x4000, 0x03, TRUE, FALSE, FALSE); // todo: verify; assumed to be the same as sn76489a
}
static DEVICE_START( sn76496 )
{
generic_start(device, 0x10000, 0x0C, TRUE, FALSE, FALSE); // todo: verify; assumed to be the same as sn76489a
generic_start(device, 0x4000, 0x03, TRUE, FALSE, FALSE); // todo: verify; assumed to be the same as sn76489a
}
static DEVICE_START( sn94624 )
{
generic_start(device, 0x10000, 0x0C, FALSE, FALSE, FALSE); // verified by plgdavid
generic_start(device, 0x4000, 0x03, FALSE, FALSE, FALSE); // verified by plgdavid
}
static DEVICE_START( ncr7496 )