From 0595773355ff282f1f8927a6c10a2f95dcdc4c8b Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Tue, 23 Aug 2022 14:41:45 -0400
Subject: [PATCH] Invents a new virtual select line for extended handling card
 ROM areas.

---
 Machines/Apple/AppleII/Card.hpp     | 10 ++++++---
 Machines/Apple/AppleII/SCSICard.cpp | 34 ++++++++++++++++++++++++-----
 2 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/Machines/Apple/AppleII/Card.hpp b/Machines/Apple/AppleII/Card.hpp
index 3a3a784d7..386e5d657 100644
--- a/Machines/Apple/AppleII/Card.hpp
+++ b/Machines/Apple/AppleII/Card.hpp
@@ -42,9 +42,13 @@ class Card {
 	public:
 		virtual ~Card() {}
 		enum Select: int {
-			None	= 0,		// No select line is active.
-			IO		= 1 << 0,	// IO select is active; i.e. access is in range $C0x0 to $C0xf.
-			Device	= 1 << 1,	// Device select is active; i.e. access is in range $Cx00 to $Cxff.
+			None		= 0,		// No select line is active.
+			IO			= 1 << 0,	// IO select is active; i.e. access is in range $C0x0 to $C0xf.
+			Device		= 1 << 1,	// Device select is active; i.e. access is in range $Cx00 to $Cxff.
+
+			C8Region	= 1 << 2,	// Access is to the region $c800 to $cfff, was preceded by at least
+									// one Device access to this card, and has not yet been followed up
+									// by an access to $cfff.
 		};
 
 		/*!
diff --git a/Machines/Apple/AppleII/SCSICard.cpp b/Machines/Apple/AppleII/SCSICard.cpp
index de2560ae9..2d0dac720 100644
--- a/Machines/Apple/AppleII/SCSICard.cpp
+++ b/Machines/Apple/AppleII/SCSICard.cpp
@@ -73,8 +73,7 @@ SCSICard::SCSICard(ROM::Map &map) : scsi_bus_(1), ncr5380_(scsi_bus_, 1) {
 
 void SCSICard::perform_bus_operation(Select select, bool is_read, uint16_t address, uint8_t *value) {
 	switch(select) {
-		case Select::None:
-		break;
+		default: break;
 
 		case Select::Device:
 			if(is_read) {
@@ -85,8 +84,8 @@ void SCSICard::perform_bus_operation(Select select, bool is_read, uint16_t addre
 		case Select::IO:
 			address &= 0xf;
 			switch(address) {
-				case 0:	case 1:	case 2:	case 3:
-				case 4:	case 5:	case 6:	case 7:
+				case 0x0:	case 0x1:	case 0x2:	case 0x3:
+				case 0x4:	case 0x5:	case 0x6:	case 0x7:
 					if(is_read) {
 						*value = ncr5380_.read(address);
 					} else {
@@ -94,12 +93,35 @@ void SCSICard::perform_bus_operation(Select select, bool is_read, uint16_t addre
 					}
 				break;
 
+				case 0xa:
+					// RAM and ROM select.
+					if(!is_read) {
+						const auto rom_base = size_t((*value & 0x0f) << 10);
+						const auto ram_base = size_t((*value & 0x70) << 6);
+
+						rom_pointer_ = &rom_[rom_base];
+						ram_pointer_ = &ram_[ram_base];
+					}
+				break;
+
 				default:
 					printf("Unhandled: %04x %c %02x\n", address, is_read ? 'r' : 'w', *value);
 				break;
 			}
 		break;
-	}
 
-	// TODO: is it extra-contractual to respond in 0xc800 to 0xd000? Clarify.
+		case Select::C8Region:
+			if(address & 0x400) {
+				if(is_read) {
+					*value = rom_pointer_[address & 0x3ff];
+				}
+			} else {
+				if(is_read) {
+					*value = ram_pointer_[address & 0x3ff];
+				} else {
+					ram_pointer_[address & 0x3ff] = *value;
+				}
+			}
+		break;
+	}
 }