From 4fc25fb7988f42456eebe03ab675433fd54c3297 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 7 Nov 2021 05:18:54 -0800
Subject: [PATCH] Adds basic shift input.

---
 Components/6526/6526.hpp                      |  9 +++++--
 .../Implementation/6526Implementation.hpp     | 26 ++++++++++++++++---
 .../6526/Implementation/6526Storage.hpp       |  1 +
 3 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/Components/6526/6526.hpp b/Components/6526/6526.hpp
index 1a48ced32..99eb5e8e6 100644
--- a/Components/6526/6526.hpp
+++ b/Components/6526/6526.hpp
@@ -40,10 +40,13 @@ enum class Personality {
 };
 
 template <typename PortHandlerT, Personality personality> class MOS6526:
-	private MOS6526Storage
+	private MOS6526Storage,
+	private Serial::Line<true>::ReadDelegate
 {
 	public:
-		MOS6526(PortHandlerT &port_handler) noexcept : port_handler_(port_handler) {}
+		MOS6526(PortHandlerT &port_handler) noexcept : port_handler_(port_handler) {
+			serial_input.set_read_delegate(this);
+		}
 		MOS6526(const MOS6526 &) = delete;
 
 		/// Writes @c value to the register at @c address. Only the low two bits of the address are decoded.
@@ -79,6 +82,8 @@ template <typename PortHandlerT, Personality personality> class MOS6526:
 		void update_interrupts();
 		void posit_interrupt(uint8_t mask);
 		void advance_counters(int);
+
+		bool serial_line_did_produce_bit(Serial::Line<true> *line, int bit) final;
 };
 
 }
diff --git a/Components/6526/Implementation/6526Implementation.hpp b/Components/6526/Implementation/6526Implementation.hpp
index f7e5bd619..f66734da2 100644
--- a/Components/6526/Implementation/6526Implementation.hpp
+++ b/Components/6526/Implementation/6526Implementation.hpp
@@ -120,6 +120,10 @@ void MOS6526<BusHandlerT, personality>::write(int address, uint8_t value) {
 		case 14:
 			counter_[0].template set_control<false>(value);
 			tod_.template set_control<false>(value);
+			if(shifter_is_output_ != bool(value & 0x40)) {
+				shifter_is_output_ = value & 0x40;
+				shift_bits_ = 0;
+			}
 		break;
 		case 15:
 			counter_[1].template set_control<true>(value);
@@ -173,9 +177,7 @@ uint8_t MOS6526<BusHandlerT, personality>::read(int address) {
 		case 11:	return tod_.template read<3>();
 
 		// Shift register.
-		case 12:
-			printf("TODO: read from shift register\n");
-		break;
+		case 12:	return shift_data_;
 
 		default:
 			printf("Unhandled 6526 read from %d\n", address);
@@ -216,6 +218,24 @@ void MOS6526<BusHandlerT, personality>::advance_tod(int count) {
 	}
 }
 
+template <typename BusHandlerT, Personality personality>
+bool MOS6526<BusHandlerT, personality>::serial_line_did_produce_bit(Serial::Line<true> *, int bit) {
+	// TODO: post CNT change; might affect timer.
+
+	if(!shifter_is_output_) {
+		shift_register_ = uint8_t((shift_register_ << 1) | bit);
+		++shift_bits_;
+
+		if(shift_bits_ == 8) {
+			shift_bits_ = 0;
+			shift_data_ = shift_register_;
+			posit_interrupt(Interrupts::SerialPort);
+		}
+	}
+
+	return true;
+}
+
 }
 }
 
diff --git a/Components/6526/Implementation/6526Storage.hpp b/Components/6526/Implementation/6526Storage.hpp
index 3f7b840be..7a3c2bf1b 100644
--- a/Components/6526/Implementation/6526Storage.hpp
+++ b/Components/6526/Implementation/6526Storage.hpp
@@ -189,6 +189,7 @@ struct MOS6526Storage {
 	uint8_t shift_data_ = 0;
 	uint8_t shift_register_ = 0;
 	int shift_bits_ = 0;
+	bool shifter_is_output_ = false;
 
 	struct Counter {
 		uint16_t reload = 0;