From 68dbd42a24f56640642423f0e57fc9951ea819b9 Mon Sep 17 00:00:00 2001
From: Dirk Best <mail@dirk-best.de>
Date: Wed, 4 Aug 2021 13:04:00 +0200
Subject: [PATCH] z8536: Better daisy chain support, fix port assignment when
 writing data

---
 src/devices/machine/z8536.cpp | 34 ++++++++++++++++++++++++++++++----
 src/devices/machine/z8536.h   |  1 -
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/src/devices/machine/z8536.cpp b/src/devices/machine/z8536.cpp
index 5074d82ccf7..fe1a91ff631 100644
--- a/src/devices/machine/z8536.cpp
+++ b/src/devices/machine/z8536.cpp
@@ -919,6 +919,32 @@ void cio_base_device::device_timer(emu_timer &timer, device_timer_id id, int par
 
 int z8536_device::z80daisy_irq_state()
 {
+	static const int prio[] =
+	{
+		COUNTER_TIMER_3_COMMAND_AND_STATUS,
+		PORT_A_COMMAND_AND_STATUS,
+		COUNTER_TIMER_2_COMMAND_AND_STATUS,
+		PORT_B_COMMAND_AND_STATUS,
+		COUNTER_TIMER_1_COMMAND_AND_STATUS
+	};
+
+	if (m_register[MASTER_INTERRUPT_CONTROL] & MICR_MIE)
+	{
+		for (int i = 0; i < 5; i++)
+		{
+			if (m_register[prio[i]] & PCS_IUS)
+			{
+				// we are currently servicing an interrupt request
+				return Z80_DAISY_IEO;
+			}
+			else if ((m_register[prio[i]] & PCS_IE) && (m_register[prio[i]] & PCS_IP))
+			{
+				// indicate that we have an interrupt request waiting
+				return Z80_DAISY_INT;
+			}
+		}
+	}
+
 	return 0;
 }
 
@@ -1081,19 +1107,19 @@ void z8536_device::write(offs_t offset, u8 data)
 	{
 		switch (offset & 0x03)
 		{
-		case PORT_C:
+		case 0:
 			write_register(PORT_C_DATA, data);
 			break;
 
-		case PORT_B:
+		case 1:
 			write_register(PORT_B_DATA, data);
 			break;
 
-		case PORT_A:
+		case 2:
 			write_register(PORT_A_DATA, data);
 			break;
 
-		case CONTROL:
+		case 3:
 			if (m_state0)
 			{
 				// state 0: write pointer
diff --git a/src/devices/machine/z8536.h b/src/devices/machine/z8536.h
index 47c6545b670..487d9b771e0 100644
--- a/src/devices/machine/z8536.h
+++ b/src/devices/machine/z8536.h
@@ -381,7 +381,6 @@ protected:
 	void match_pattern(int port);
 	void external_port_w(int port, int bit, int state);
 
-private:
 	devcb_write_line       m_write_irq;
 
 	devcb_read8            m_read_pa;