leonardo/renaissa: correct ACK output

src/devices/bus/odyssey2/homecomp.cpp

@@ -9,7 +9,7 @@ be inserted into the Odyssey 2/G7000.
 
 Hardware notes:
 - Z80 @ 3.547MHz
-- 2*8KB ROM, 16KB RAM(2*TMS4416, 2 unpopulated sockets)
+- 2*8KB ROM, 16KB RAM(2*TMS4416, 2 unpopulated locations)
 - optional data recorder
 
 The RAM can be expanded to 32KB by simply adding two more TMS4416. To enable it,

src/devices/bus/saitek_osa/maestro.cpp

@@ -26,7 +26,6 @@ higher speed versions, they overclocked the CPU. And if the CPU couldn't
 handle the overclock well enough, they went for a slightly lower speed XTAL.
 
 TODO:
-- does not work if cpu speed is 4MHz
 - cpu clock divider after writing to 0x2000/0x2200
 
 ***************************************************************************/
@@ -284,7 +283,7 @@ void saitekosa_maestro_device::control_w(u8 data)
 
 u8 saitekosa_maestro_device::ack_r()
 {
-	// d6: ?
+	// d6: _Vcc
 	// d7: ACK-P
 	return m_expansion->ack_state() ? 0x80 : 0x00;
 }

src/devices/bus/saitek_osa/maestroa.cpp

@@ -17,9 +17,6 @@ Hardware notes:
 The CPU is a 4MHz part, higher speed modules overclock it. The PCB is not
 compatible for upgrading to newer Maestro versions.
 
-TODO:
-- does not work if cpu speed is 4MHz
-
 ***************************************************************************/
 
 #include "emu.h"

src/mame/saitek/leonardo.cpp

@@ -46,10 +46,9 @@ The H8 Brute Force module doesn't work with the 1st program version of Leonardo,
 this is mentioned in the repair manual and it says it requires an EPROM upgrade.
 The Sparc module doesn't appear to work with it either. Moreover, the Sparc module
 manual mentions that for it to work properly on Leonardo, the chesscomputer needs
-to be upgraded with an EMI PCB (power supply related).
+to be upgraded with an EMI PCB (power supply related, meaningless for emulation).
 
 TODO:
-- OSA module comms is not completely understood
 - OSA PC link, uses MCU serial interface
 - add nvram (MCU port $14?)
 - add power-off, not useful with missing nvram support
@@ -122,12 +121,16 @@ private:
 	u8 p5_r();
 	void p6_w(u8 data);
 
+	int m_ack_state = 0;
+	int m_rts_state = 0;
 	u8 m_inp_mux = 0;
 	u8 m_led_data[2] = { };
 };
 
 void leo_state::machine_start()
 {
+	save_item(NAME(m_ack_state));
+	save_item(NAME(m_rts_state));
 	save_item(NAME(m_inp_mux));
 	save_item(NAME(m_led_data));
 }
@@ -183,7 +186,10 @@ void leo_state::unk_w(u8 data)
 
 void leo_state::exp_rts_w(int state)
 {
-	// NAND with ACK-P (not used by chesscomputer?)
+	// recursive NAND with ACK-P
+	if (state && m_ack_state)
+		m_expansion->ack_w(m_ack_state);
+	m_rts_state = state;
 }
 
 
@@ -225,8 +231,11 @@ void leo_state::p5_w(u8 data)
 	// d3: NAND with STB-P
 	m_stb->in_w<1>(BIT(data, 3));
 
-	// d5: expansion ACK-P
-	m_expansion->ack_w(BIT(data, 5));
+	// d5: expansion ACK-P (recursive NAND with RTS-P)
+	int ack_state = BIT(data, 5);
+	if (m_rts_state || !ack_state)
+		m_expansion->ack_w(ack_state);
+	m_ack_state = ack_state;
 
 	// d6,d7: chessboard led row data
 	m_led_data[0] = (m_led_data[0] & 3) | (~data >> 4 & 0xc);

src/mame/saitek/renaissance.cpp

@@ -108,6 +108,8 @@ private:
 	u8 p6_r();
 	void p6_w(u8 data);
 
+	int m_ack_state = 0;
+	int m_rts_state = 0;
 	u8 m_inp_mux = 0;
 	u8 m_led_data[2] = { };
 };
@@ -116,6 +118,8 @@ void ren_state::machine_start()
 {
 	m_out_lcd.resolve();
 
+	save_item(NAME(m_ack_state));
+	save_item(NAME(m_rts_state));
 	save_item(NAME(m_inp_mux));
 	save_item(NAME(m_led_data));
 }
@@ -200,7 +204,10 @@ u8 ren_state::control_r()
 
 void ren_state::exp_rts_w(int state)
 {
-	// NAND with ACK-P (not used by chesscomputer?)
+	// recursive NAND with ACK-P
+	if (state && m_ack_state)
+		m_expansion->ack_w(m_ack_state);
+	m_rts_state = state;
 }
 
 
@@ -243,8 +250,11 @@ void ren_state::p5_w(u8 data)
 	// d3: NAND with STB-P
 	m_stb->in_w<1>(BIT(data, 3));
 
-	// d5: expansion ACK-P
-	m_expansion->ack_w(BIT(data, 5));
+	// d5: expansion ACK-P (recursive NAND with RTS-P)
+	int ack_state = BIT(data, 5);
+	if (m_rts_state || !ack_state)
+		m_expansion->ack_w(ack_state);
+	m_ack_state = ack_state;
 
 	// d0: power-off on falling edge
 	m_expansion->pw_w(data & 1);