Added:

* calculate data/instruction physical addresses from a virtual address
	memory_addresses_t calculate_physical_address(const int run_mode, const uint16_t a);

* check if a 'memory_address_t'-address would cause a fault
	void check_address(const bool trap_on_failure, const bool is_write, const memory_addresses_t & addr, const bool word_mode, const bool is_data, const int run_mode);

bus.cpp

@@ -324,6 +324,146 @@ void bus::setMMR2(const uint16_t value)
 	MMR2 = value;
 }
 
+memory_addresses_t bus::calculate_physical_address(const int run_mode, const uint16_t a)
+{
+	const uint8_t apf = a >> 13; // active page field
+
+	uint32_t physical_instruction = pages[run_mode][0][apf].par * 64;
+	uint32_t physical_data        = pages[run_mode][1][apf].par * 64;
+
+	uint16_t p_offset = a & 8191;  // page offset
+
+	physical_instruction += p_offset;
+	physical_data        += p_offset;
+
+	if (MMR0 & 1) {  // MMU enabled?
+		if ((MMR3 & 16) == 0) {  // offset is 18bit
+			physical_instruction &= 0x3ffff;
+			physical_data        &= 0x3ffff;
+		}
+	}
+
+	return { a, apf, physical_instruction, physical_data };
+}
+
+void bus::check_address(const bool trap_on_failure, const bool is_write, const memory_addresses_t & addr, const bool word_mode, const bool is_data, const int run_mode)
+{
+	// check for odd address access
+	if ((addr.virtual_address & 1) && word_mode == 0) {
+		if (is_write)
+			pages[run_mode][is_data][addr.apf].pdr |= 1 << 7;
+
+		c->schedule_trap(004);  // invalid access
+
+		throw 5;
+	}
+
+	if (!trap_on_failure)
+		return;
+
+	// check access to page
+	if ((MMR0 & (1 << 9)) || c->get_34()) {
+		const int access_control = pages[run_mode][is_data][addr.apf].pdr & 7;
+
+		// write
+		if (is_write && access_control != 6) {
+			c->schedule_trap(0250);  // invalid address
+
+			if (is_write)
+				pages[run_mode][is_data][addr.apf].pdr |= 1 << 7;
+
+			if ((MMR0 & 0160000) == 0) {
+				MMR0 &= 017777;
+				MMR0 |= 1 << 13;  // read-only
+
+				MMR0 &= ~(3 << 5);
+				MMR0 |= run_mode << 5;  // TODO: kernel-mode or user-mode when a trap occurs in user-mode?
+
+				MMR0 &= ~14;  // add current page
+				MMR0 |= addr.apf << 1;
+			}
+
+			DOLOG(debug, true, "MMR0: %06o", MMR0);
+
+			throw 1;
+		}
+
+		// read
+		if (!is_write) {
+			if (access_control == 0 || access_control == 1 || access_control == 3 || access_control == 4 || access_control == 7) {
+				c->schedule_trap(0250);  // invalid address
+
+				if (is_write)
+					pages[run_mode][is_data][addr.apf].pdr |= 1 << 7;  // TODO: D/I
+
+				if ((MMR0 & 0160000) == 0) {
+					MMR0 &= 017777;
+
+					if (access_control == 0 || access_control == 4)
+						MMR0 |= 1 << 15;  // not resident
+					else
+						MMR0 |= 1 << 13;  // read-only
+
+					MMR0 &= ~(3 << 5);
+					MMR0 |= run_mode << 5;
+
+					MMR0 &= ~14;  // add current page
+					MMR0 |= addr.apf << 1;
+				}
+
+				throw 2;
+			}
+		}
+	}
+
+	// beyond physical range?
+	if ((is_data && addr.physical_data >= n_pages * 8192) || (!is_data && addr.physical_instruction >= n_pages * 8192)) {
+		if ((MMR0 & 0160000) == 0) {
+			MMR0 &= 017777;
+			MMR0 |= 1 << 15;  // non-resident
+
+			MMR0 &= ~14;  // add current page
+			MMR0 |= addr.apf << 1;
+
+			MMR0 &= ~(3 << 5);
+			MMR0 |= run_mode << 5;
+		}
+
+		if (is_write)
+			pages[run_mode][is_data][addr.apf].pdr |= 1 << 7;  // TODO: D/I
+
+		c->schedule_trap(04);
+
+		throw 3;
+	}
+
+	// check if invalid access IN a page
+	uint16_t pdr_len = (pages[run_mode][is_data][addr.apf].pdr >> 8) & 127;
+	uint16_t pdr_cmp = (addr.virtual_address >> 6) & 127;
+
+	bool direction = pages[run_mode][is_data][addr.apf].pdr & 8;  // TODO: D/I
+
+	if ((pdr_cmp > pdr_len && direction == false) || (pdr_cmp < pdr_len && direction == true)) {
+		c->schedule_trap(0250);  // invalid access
+
+		if ((MMR0 & 0160000) == 0) {
+			MMR0 &= 017777;
+			MMR0 |= 1 << 14;  // length
+
+			MMR0 &= ~14;  // add current page
+			MMR0 |= addr.apf << 1;
+
+			MMR0 &= ~(3 << 5);
+			MMR0 |= run_mode << 5;
+		}
+
+		if (is_write)
+			pages[run_mode][0][addr.apf].pdr |= 1 << 7;  // TODO: D/I
+
+		throw 4;
+	}
+}
+
 uint32_t bus::calculate_physical_address(const int run_mode, const uint16_t a, const bool trap_on_failure, const bool is_write, const bool peek_only, const bool is_data)
 {
 	uint32_t m_offset = a;

bus.h

@@ -57,8 +57,14 @@ class tty;
 
 typedef enum { d_space, i_space } d_i_space_t;
 
-typedef struct
+typedef struct {
-{
+	uint16_t virtual_address;
+	uint8_t  apf;  // active page field
+	uint32_t physical_instruction;
+	uint32_t physical_data;
+} memory_addresses_t;
+
+typedef struct {
 	uint16_t par, pdr;
 } page_t;
 
@@ -140,4 +146,7 @@ public:
 	uint16_t get_switch_register() const { return switch_register; }
 
 	uint32_t calculate_physical_address(const int run_mode, const uint16_t a, const bool trap_on_failure, const bool is_write, const bool peek_only, const bool is_data);
+
+	memory_addresses_t calculate_physical_address(const int run_mode, const uint16_t a);
+	void check_address(const bool trap_on_failure, const bool is_write, const memory_addresses_t & addr, const bool word_mode, const bool is_data, const int run_mode);
 };