From df29a50738a9099361f000fcad00511e777434e5 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Wed, 31 Aug 2022 15:33:48 -0400
Subject: [PATCH] Attempt to support the DMA interface.

---
 Components/5380/ncr5380.cpp         | 37 +++++++++++++++++++++--------
 Components/5380/ncr5380.hpp         |  9 +++++++
 Machines/Apple/AppleII/SCSICard.cpp | 16 +++++++++++++
 3 files changed, 52 insertions(+), 10 deletions(-)

diff --git a/Components/5380/ncr5380.cpp b/Components/5380/ncr5380.cpp
index 7c4d14829..f6f35d13e 100644
--- a/Components/5380/ncr5380.cpp
+++ b/Components/5380/ncr5380.cpp
@@ -33,14 +33,10 @@ void NCR5380::write(int address, uint8_t value, bool) {
 	switch(address & 7) {
 		case 0:
 			LOG("[SCSI 0] Set current SCSI bus state to " << PADHEX(2) << int(value));
-			data_bus_ = value;
 
+			data_bus_ = value;
 			if(dma_request_ && dma_operation_ == DMAOperation::Send) {
-//				printf("w %02x\n", value);
-				dma_acknowledge_ = true;
-				dma_request_ = false;
-				update_control_output();
-				bus_.set_device_output(device_id_, bus_output_);
+				dma_acknowledge(value);
 			}
 		break;
 
@@ -143,10 +139,7 @@ uint8_t NCR5380::read(int address, bool) {
 			LOG("[SCSI 0] Get current SCSI bus state: " << PADHEX(2) << (bus_.get_state() & 0xff));
 
 			if(dma_request_ && dma_operation_ == DMAOperation::InitiatorReceive) {
-				dma_acknowledge_ = true;
-				dma_request_ = false;
-				update_control_output();
-				bus_.set_device_output(device_id_, bus_output_);
+				return dma_acknowledge();
 			}
 		return uint8_t(bus_.get_state());
 
@@ -324,3 +317,27 @@ void NCR5380::set_execution_state(ExecutionState state) {
 size_t NCR5380::scsi_id() {
 	return device_id_;
 }
+
+bool NCR5380::dma_request() {
+	return dma_request_;
+}
+
+uint8_t NCR5380::dma_acknowledge() {
+	const uint8_t bus_state = uint8_t(bus_.get_state());
+
+	dma_acknowledge_ = true;
+	dma_request_ = false;
+	update_control_output();
+	bus_.set_device_output(device_id_, bus_output_);
+
+	return bus_state;
+}
+
+void NCR5380::dma_acknowledge(uint8_t value) {
+	data_bus_ = value;
+
+	dma_acknowledge_ = true;
+	dma_request_ = false;
+	update_control_output();
+	bus_.set_device_output(device_id_, bus_output_);
+}
diff --git a/Components/5380/ncr5380.hpp b/Components/5380/ncr5380.hpp
index 65f01c6a9..7f51bb810 100644
--- a/Components/5380/ncr5380.hpp
+++ b/Components/5380/ncr5380.hpp
@@ -33,6 +33,15 @@ class NCR5380 final: public SCSI::Bus::Observer {
 		/*! @returns The SCSI ID assigned to this device. */
 		size_t scsi_id();
 
+		/*! @return @c true if DMA request is active; @c false otherwise. */
+		bool dma_request();
+
+		/*! Signals DMA acknowledge with a simultaneous read. */
+		uint8_t dma_acknowledge();
+
+		/*! Signals DMA acknowledge with a simultaneous write. */
+		void dma_acknowledge(uint8_t);
+
 	private:
 		SCSI::Bus &bus_;
 
diff --git a/Machines/Apple/AppleII/SCSICard.cpp b/Machines/Apple/AppleII/SCSICard.cpp
index 0c5dbd43e..f24b7115d 100644
--- a/Machines/Apple/AppleII/SCSICard.cpp
+++ b/Machines/Apple/AppleII/SCSICard.cpp
@@ -103,6 +103,15 @@ void SCSICard::perform_bus_operation(Select select, bool is_read, uint16_t addre
 					}
 				break;
 
+				case 0x8:
+					// DMA acknowledge.
+					if(is_read) {
+						*value = ncr5380_.dma_acknowledge();
+					} else {
+						ncr5380_.dma_acknowledge(*value);
+					}
+				break;
+
 				case 0xa:
 					// RAM and ROM select.
 					if(!is_read) {
@@ -114,6 +123,13 @@ void SCSICard::perform_bus_operation(Select select, bool is_read, uint16_t addre
 					}
 				break;
 
+				case 0xe:
+					// DRQ in b7.
+					if(is_read) {
+						*value = ncr5380_.dma_request() ? 0x80 : 0x00;
+					}
+				break;
+
 				default:
 					printf("Unhandled: %04x %c %02x\n", address, is_read ? 'r' : 'w', *value);
 				break;