From 9cf92379d5fcf0076c25dae0935daab446c992cd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Karel=20Ko=C4=8D=C3=AD?= <cynerd@email.cz>
Date: Wed, 30 Aug 2017 21:37:53 +0200
Subject: Initial commit

Adding work done so far.
---
 qtmips_machine/programmemory.cpp | 111 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 qtmips_machine/programmemory.cpp

(limited to 'qtmips_machine/programmemory.cpp')

diff --git a/qtmips_machine/programmemory.cpp b/qtmips_machine/programmemory.cpp
new file mode 100644
index 0000000..c5ef53a
--- /dev/null
+++ b/qtmips_machine/programmemory.cpp
@@ -0,0 +1,111 @@
+#include "programmemory.h"
+#include <sstream>
+#include "qtmipsexception.h"
+#include "instructions/arithmetic.h"
+#include "instructions/loadstore.h"
+#include "instructions/nop.h"
+#include "instructions/shift.h"
+
+ProgramMemory::ProgramMemory(ProgramLoader *loader, MemoryAccess *memory) {
+    this->memory = memory;
+    // Load program to memory (just dump it byte by byte, decode is done on demand)
+    for (int i = 0; i < loader->get_nsec(); i++) {
+        std::uint32_t base_address = loader->get_address(i);
+        std::vector<std::uint8_t> data = loader->get_data(i);
+        for (auto it = data.begin(); it < data.end(); it++) {
+            memory->write_byte(base_address + i, *it);
+        }
+    }
+}
+
+#define MASKSUB(VAR, LEN, OFFSET) ((VAR & ~((1 << (LEN+OFFSET+1)) - 1)) >> OFFSET)
+
+Instruction *ProgramMemory::at(std::uint32_t address) {
+    if (address % 4)
+        // TODO different exception (unaligned address)
+        throw std::exception();
+    // Read instruction from memory
+    std::uint32_t dt = this->memory->read_word(address);
+
+    // Decode instruction
+    Instruction *inst;
+    std::uint8_t opcode = dt >> 26; // upper 6 bits
+    if (opcode == 0) { // Arithmetic and shift instructions
+        return this->decode_r(dt);
+    } else if (opcode == 2 || opcode == 3) { // Jump instructions
+        return decode_j(dt);
+    } else {
+        return decode_i(dt);
+    }
+}
+
+// TODO implement
+#define I_UNKNOWN(DATA) do { std::stringstream ss; ss << std::hex << DATA; throw QTMIPS_EXCEPTION(UnsupportedInstruction, "Unknown instruction, can't decode", ss.str());  } while(false);
+#define I_UNSUPPORTED(INST) throw QTMIPS_EXCEPTION(UnsupportedInstruction, "Decoded unsupported unstruction", #INST)
+
+Instruction *ProgramMemory::decode_r(std::uint32_t dt) {
+        std::uint8_t func = MASKSUB(dt, 6, 0);
+        if (!func)
+            return new InstructionNop();
+
+        std::uint8_t rs, rt, rd, sa;
+        rs = MASKSUB(dt, 5, 21);
+        rt = MASKSUB(dt, 5, 16);
+        rd = MASKSUB(dt, 5, 11);
+        sa = MASKSUB(dt, 5, 6);
+
+        if (func < 8) { // Shift instructions
+            bool variable = false;
+            enum InstructionShiftT t;
+            switch (func) {
+            case 0:
+                t = IST_LL;
+                break;
+            case 2:
+                t = IST_RL;
+                break;
+            case 3:
+                t = IST_RA;
+                break;
+            case 4:
+                t = IST_LL;
+                variable = true;
+                break;
+            case 6:
+                t = IST_RL;
+                variable = true;
+                break;
+            case 7:
+                t = IST_RA;
+                variable = true;
+                break;
+            default:
+                I_UNKNOWN(dt);
+            }
+            if (variable)
+                return new InstructionShiftVariable(t, rs, rt, rd);
+            else
+                return new InstructionShift(t, rt, rd, sa);
+        } else if (func < 10) { // Jump instructions
+            // TODO
+            I_UNKNOWN(dt);
+        } else { // TODO filter rest
+            I_UNKNOWN(dt);
+        }
+}
+
+Instruction *ProgramMemory::decode_j(std::uint32_t dt) {
+    std::uint32_t address = MASKSUB(dt, 26, 0);
+    // TODO
+    I_UNKNOWN(dt);
+}
+
+Instruction *ProgramMemory::decode_i(std::uint32_t dt) {
+    // InstructionI
+    std::uint8_t rs, rt;
+    rs = MASKSUB(dt, 5, 21);
+    rt = MASKSUB(dt, 5, 16);
+    std::uint16_t immediate = MASKSUB(dt, 16, 0);
+    // TODO
+    I_UNKNOWN(dt);
+}
-- 
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