sega/megadriv.cpp: later Acclaim sport games fails i2c checks during POST

[angelosa]

I think what NBA Jam TE and friends are trying to achieve at POST is just an i2c bus check. The device is never driven in a state for reading the actual data inside, it's not using the SCL in a meaningful way while continuously hopping the SDA high then low in idle state. Follows a rough draft:

diff --git a/src/devices/machine/i2cmem.cpp b/src/devices/machine/i2cmem.cpp

index d6fbe779618..75d012226ce 100644

--- a/src/devices/machine/i2cmem.cpp

+++ b/src/devices/machine/i2cmem.cpp

@@ -316,7 +316,7 @@ void i2cmem_device::write_sda(int state)

 	state &= 1;

 	if( m_sdaw != state )

 	{

-		LOGMASKED( LOG_WRITELINE, "%s: SDA = %d @ %s\n", machine().describe_context(), state, machine().time().to_string() );

+		LOGMASKED( LOG_WRITELINE, "%s: SDA = %d @ %s (%d)\n", machine().describe_context(), state, machine().time().to_string(), state );

 		m_sdaw = state;

 

 		// Ignore transitions on SDA while device is driving it low

@@ -352,7 +352,7 @@ void i2cmem_device::write_scl(int state)

 	if( m_scl != state )

 	{

 		m_scl = state;

-		LOGMASKED( LOG_WRITELINE, "%s: SCL = %d @ %s\n", machine().describe_context(), m_scl, machine().time().to_string() );

+		LOGMASKED( LOG_WRITELINE, "%s: SCL = %d @ %s (%d)\n", machine().describe_context(), m_scl, machine().time().to_string(), m_state );

 

 		switch( m_state )

 		{

@@ -567,8 +567,10 @@ void i2cmem_device::write_wc(int state)

 int i2cmem_device::read_sda()

 {

 	int res = m_sdar & 1;

+	if (m_state == STATE_IDLE)

+		res = m_sdaw & 1;

 	if( !machine().side_effects_disabled() )

-		LOGMASKED( LOG_READLINE, "%s: SDA = %d\n", machine().describe_context(), res );

+		LOGMASKED( LOG_READLINE, "%s: SDA = %d (%d)\n", machine().describe_context(), res, m_state );

 

 	return res;

 }

i2c device operations happens normally when viewing records in options (and I guess when it saves, given I managed to initialize correctly).

Originally posted by @angelosa in 6c9d79d

List of known games affected:
hash/megadriv.xml

• bighurt
• blockb
• collslam
• nbajam, nbajamj, nbajamp (currently using a i2c own implementation in place thru rom_nbajam_alt)
• nbajamte, nbajamtef
• nflqb
• nflqb96

hash/32x.xml

• nbajamte
• nflqb (assumed, currently fails earlier)

[dinkc64]

@angelosa,
That's exactly how I have it impl'd in my i2c eeprom, and maintains full compatibility without side-effects

[angelosa]

May as well push it to master branch while we are early in release cycle.