From 83e223e2bd46701b124887361a5431e4ccd5512d Mon Sep 17 00:00:00 2001
From: folkert van heusden <mail@vanheusden.com>
Date: Sat, 26 Mar 2022 17:55:02 +0100
Subject: [PATCH] limit to 22b if bit 4 of mmr3 is not set

---
 bus.cpp | 39 +++++++++++++++++++++++++++++++++------
 1 file changed, 33 insertions(+), 6 deletions(-)

diff --git a/bus.cpp b/bus.cpp
index 05a257f..f18f539 100644
--- a/bus.cpp
+++ b/bus.cpp
@@ -53,6 +53,7 @@ void bus::clearmem()
 void bus::init()
 {
 	MMR0 = 0;
+	MMR3 = 0;
 }
 
 uint16_t bus::read(const uint16_t a, const bool word_mode, const bool use_prev)
@@ -316,21 +317,34 @@ uint16_t bus::read(const uint16_t a, const bool word_mode, const bool use_prev)
 
 	uint16_t pdr_len = (((pages[run_mode][apf].pdr >> 8) & 127) + 1) * 64;
 
-	if (p_offset >= pdr_len && (MMR0 & 1)) {
+	bool direction = !!(pages[run_mode][apf].pdr & 8);
+
+	if ((p_offset >= pdr_len && (MMR0 & 1) && direction == false) || (p_offset < pdr_len && (MMR0 & 1) && direction == true)) {
 		D(fprintf(stderr, "bus::read::p_offset %o >= %o\n", p_offset, pdr_len);)
-		c->schedule_trap(04);  // invalid address
+		c->schedule_trap(0250);  // invalid access
+
+		pages[run_mode][apf].pdr |= 1 << 7;
+
+		MMR2 = c->getPC();
 	}
 	else if (m_offset >= n_pages * 8192) {
 		D(fprintf(stderr, "bus::read %o >= %o\n", m_offset, n_pages * 8192);)
 		c->schedule_trap(04);  // invalid address
+
+		pages[run_mode][apf].pdr |= 1 << 7;
+
+		MMR2 = c->getPC();
 	}
 
+	if (direction == false)  // 18 bit
+		m_offset &= 01777777777;
+
 	if (word_mode)
 		temp = m -> readByte(m_offset);
 	else
 		temp = m -> readWord(m_offset);
 
-	D(fprintf(stderr, "BUS read from %o (pages: %o/%o/%o, run mode %d, apf %d, PDR: %06o): %06o\n", m_offset, pages[run_mode][apf].par, pages[run_mode][apf].par * 64, n_pages * 8192, run_mode, apf, pages[run_mode][apf].pdr, temp);)
+	D(fprintf(stderr, "BUS read from %o (pages: %o/%o/%o, run mode %d, apf %d, PDR: %06o, b22: %d): %06o\n", m_offset, pages[run_mode][apf].par, pages[run_mode][apf].par * 64, n_pages * 8192, run_mode, apf, pages[run_mode][apf].pdr, MMR3 & 16, temp);)
 
 	return temp;
 }
@@ -597,16 +611,29 @@ uint16_t bus::write(const uint16_t a, const bool word_mode, uint16_t value, cons
 
 	uint16_t pdr_len = (((pages[run_mode][apf].pdr >> 8) & 127) + 1)* 64;
 
-	if (p_offset >= pdr_len && (MMR0 & 1)) {
+	bool direction = !!(pages[run_mode][apf].pdr & 8);
+
+	if ((p_offset >= pdr_len && (MMR0 & 1) && direction == false) || (p_offset < pdr_len && (MMR0 & 1) && direction == true)) {
 		D(fprintf(stderr, "bus::write::p_offset %o >= %o\n", p_offset, pdr_len);)
-		c->schedule_trap(04);  // invalid address
+		c->schedule_trap(0250);  // invalid access
+
+		pages[run_mode][apf].pdr |= 1 << 7;
+
+		MMR2 = c->getPC();
 	}
 	else if (m_offset >= n_pages * 8192) {
 		D(fprintf(stderr, "bus::write %o >= %o\n", m_offset, n_pages * 8192);)
 		c->schedule_trap(04);  // invalid address
+
+		pages[run_mode][apf].pdr |= 1 << 7;
+
+		MMR2 = c->getPC();
 	}
 
-	D(fprintf(stderr, "BUS write to %o (pages: %o/%o/%o, run mode %d, apf %d, PDR: %06o): %06o\n", m_offset, pages[run_mode][apf].par, pages[run_mode][apf].par * 64, n_pages * 8192, run_mode, apf, pages[run_mode][apf].pdr, value);)
+	D(fprintf(stderr, "BUS write to %o (pages: %o/%o/%o, run mode %d, apf %d, PDR: %06o, b22: %d): %06o\n", m_offset, pages[run_mode][apf].par, pages[run_mode][apf].par * 64, n_pages * 8192, run_mode, apf, pages[run_mode][apf].pdr, MMR3 & 16, value);)
+
+	if (direction == false)  // 18 bit
+		m_offset &= 01777777777;
 
 	if (word_mode)
 		m->writeByte(m_offset, value);