sega/model2.cpp: TGP math lookup table logic, fixes MT09265 (#14250)

gm-matthew · web-flow · commit c2abf66a4c5f · 2025-10-03T10:02:18.000-04:00
Also remove wait state when writing to copro FIFO, no longer needed
diff --git a/src/mame/sega/model2.cpp b/src/mame/sega/model2.cpp
@@ -519,9 +519,9 @@ u32 model2_tgp_state::copro_inv_r(offs_t offset)
 	u32 result = m_copro_tgp_tables[index | 0x8000];
 	u8 bexp = (m_copro_inv_base >> 23) & 0xff;
 	u8 exp = (result >> 23) + (0x7f - bexp);
-	result = (result & 0x807fffff) | (exp << 23);
-	if(m_copro_inv_base & 0x80000000)
-		result ^= 0x80000000;
+	result = (result & 0x007fffff) | (exp << 23);
+	if (m_copro_inv_base & 0x80000000 && offset)
+		result |= 0x80000000;
 	return result;
 }
 
@@ -607,9 +607,6 @@ void model2_tgp_state::copro_fifo_w(u32 data)
 	}
 	else
 		m_copro_fifo_in->push(u32(data));
-
-	// 1 wait state for i960; prevents Manx TT course select rotation bug
-	m_maincpu->spin_until_time(attotime::from_nsec(40));
 }
 
 

Original file line number	Diff line number	Diff line change
`@@ -519,9 +519,9 @@ u32 model2_tgp_state::copro_inv_r(offs_t offset)`
`519`	`519`	`u32 result = m_copro_tgp_tables[index \| 0x8000];`
`520`	`520`	`u8 bexp = (m_copro_inv_base >> 23) & 0xff;`
`521`	`521`	`u8 exp = (result >> 23) + (0x7f - bexp);`
`522`		`- result = (result & 0x807fffff) \| (exp << 23);`
`523`		`- if(m_copro_inv_base & 0x80000000)`
`524`		`- result ^= 0x80000000;`
	`522`	`+ result = (result & 0x007fffff) \| (exp << 23);`
	`523`	`+ if (m_copro_inv_base & 0x80000000 && offset)`
	`524`	`+ result \|= 0x80000000;`
`525`	`525`	`return result;`
`526`	`526`	`}`
`527`	`527`
`@@ -607,9 +607,6 @@ void model2_tgp_state::copro_fifo_w(u32 data)`
`607`	`607`	`}`
`608`	`608`	`else`
`609`	`609`	`m_copro_fifo_in->push(u32(data));`
`610`		`-`
`611`		`- // 1 wait state for i960; prevents Manx TT course select rotation bug`
`612`		`- m_maincpu->spin_until_time(attotime::from_nsec(40));`
`613`	`610`	`}`
`614`	`611`
`615`	`612`