From 77f14fa6384f6b2bed27def9d74cd152f2759748 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Wed, 23 Oct 2019 23:09:49 -0400
Subject: [PATCH] Starts trying to make sense of interrupts.

---
 Components/68901/MFP68901.cpp | 31 ++++++++++++++++++++++----
 Components/68901/MFP68901.hpp | 41 +++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+), 4 deletions(-)

diff --git a/Components/68901/MFP68901.cpp b/Components/68901/MFP68901.cpp
index 9cef37808..e0a127cf9 100644
--- a/Components/68901/MFP68901.cpp
+++ b/Components/68901/MFP68901.cpp
@@ -26,10 +26,18 @@ uint8_t MFP68901::read(int address) {
 		case 0x02:
 			LOG("Read: data direction "  << PADHEX(2) << int(gpip_direction_));
 		return gpip_direction_;
-		case 0x03:		LOG("Read: interrupt enable A");		break;
-		case 0x04:		LOG("Read: interrupt enable B");		break;
-		case 0x05:		LOG("Read: interrupt pending A");		break;
-		case 0x06:		LOG("Read: interrupt pending B");		break;
+		case 0x03:
+			LOG("Read: interrupt enable A");
+		return interrupt_enable_[0];
+		case 0x04:
+			LOG("Read: interrupt enable B");
+		return interrupt_enable_[1];
+		case 0x05:
+			LOG("Read: interrupt pending A");
+		return interrupt_pending_[0];
+		case 0x06:
+			LOG("Read: interrupt pending B");
+		return interrupt_pending_[1];
 		case 0x07:		LOG("Read: interrupt in-service A");	break;
 		case 0x08:		LOG("Read: interrupt in-service B");	break;
 		case 0x09:		LOG("Read: interrupt mask A");			break;
@@ -209,3 +217,18 @@ void MFP68901::reevaluate_gpip_interrupts() {
 	}
 	gpip_interrupt_state_ = gpip_state;
 }
+
+
+// MARK: - Interrupts
+
+void MFP68901::begin_interrupt(Interrupt interrupt) {
+	// In service is always set.
+	interrupt_in_service_[interrupt >> 3] |= 1 << (interrupt & 7);
+
+	// Pending is set only if the interrupt is enabled.
+//	interrupt_pending_[interrupt >> 3] |=
+}
+
+void MFP68901::end_interrupt(Interrupt interrupt) {
+	// Reset in-service and pending.
+}
diff --git a/Components/68901/MFP68901.hpp b/Components/68901/MFP68901.hpp
index f7dcf7978..e69519e49 100644
--- a/Components/68901/MFP68901.hpp
+++ b/Components/68901/MFP68901.hpp
@@ -63,6 +63,47 @@ class MFP68901 {
 		uint8_t gpip_interrupt_state_ = 0;
 
 		void reevaluate_gpip_interrupts();
+
+		// MARK: - Interrupts
+
+		// Ad hoc documentation: there seems to be a four-stage process here.
+		// This is my current understanding:
+		//
+		// Interrupt in-service refers to whether the signal that would cause an
+		// interrupt is active.
+		//
+		// If the interrupt is in-service and enabled, it will be listed as pending.
+		//
+		// If a pending interrupt is enabled in the interrupt mask, it will generate
+		// a processor interrupt.
+		//
+		// So, the designers seem to have wanted to allow for polling and interrupts,
+		// and then also decided to have some interrupts be able to be completely
+		// disabled, so that don't even show up for polling.
+		uint8_t interrupt_in_service_[2] = {0, 0};
+		uint8_t interrupt_enable_[2] = {0, 0};
+		uint8_t interrupt_pending_[2] = {0, 0};
+		uint8_t interrupt_mask_[2] = {0, 0};
+
+		enum Interrupt {
+			GPIP0 = 0,
+			GPIP1,
+			GPIP2,
+			GPIP3,
+			TimerD,
+			TimerC,
+			GPIP4,
+			GPIP5,
+			TimerB,
+			TransmitError,
+			TransmitBufferEmpty,
+			ReceiveError,
+			ReceiveBufferFull,
+			GPIP6,
+			GPIP7
+		};
+		void begin_interrupt(Interrupt interrupt);
+		void end_interrupt(Interrupt interrupt);
 };
 
 }