3c_disasm/instr/branch.cpp

   1 /*   `Deep Thought', a softcore CPU implemented on a FPGA
   2
   3     Copyright (C) 2010 Markus Hofstaetter <markus.manrow@gmx.at>
   4     Copyright (C) 2010 Martin Perner <e0725782@student.tuwien.ac.at>
   5     Copyright (C) 2010 Stefan Rebernig <stefan.rebernig@gmail.com>
   6     Copyright (C) 2010 Manfred Schwarz <e0725898@student.tuwien.ac.at>
   7     Copyright (C) 2010 Bernhard Urban <lewurm@gmail.com>
   8
   9     This program is free software: you can redistribute it and/or modify
  10     it under the terms of the GNU General Public License as published by
  11     the Free Software Foundation, either version 3 of the License, or
  12     (at your option) any later version.
  13
  14     This program is distributed in the hope that it will be useful,
  15     but WITHOUT ANY WARRANTY; without even the implied warranty of
  16     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17     GNU General Public License for more details.
  18
  19     You should have received a copy of the GNU General Public License
  20     along with this program.  If not, see <http://www.gnu.org/licenses/>. */
  21
  22 #include "../Iinstr.hpp"
  23
  24 class Cbranch : public Iinstr {
  25         private:
  26                 bool m_taken;
  27                 char m_typ;
  28         public:
  29                 Cbranch();
  30                 void evalInstr();
  31                 void execInstr();
  32                 std::string toString();
  33                 Iinstr* getNew();
  34 };
  35
  36 /**
  37  * Name:      create_instruction
  38  * Purpose:   if compiled as shared library, this functions creates the
  39               instruction object
  40
  41  * Returns:   pointer to instruction object
  42  */
  43 extern "C" Iinstr* create_instruction() {
  44     return new Cbranch();
  45 }
  46
  47 Iinstr* Cbranch::getNew()
  48 {
  49         return new Cbranch();
  50 }
  51 /**
  52  * Name:      destroy_instruction
  53  * Purpose:   if compiled as shared library, this functions destoys the
  54               instruction object
  55
  56  * Parameter: IInstruction - the instruction object to delete
  57  */
  58 extern "C" void destroy_instruction(Iinstr* p) {
  59     delete p;
  60 }
  61
  62 Cbranch::Cbranch() : m_taken(1), m_typ(0)
  63 {
  64         opcode = B5(10110);
  65         name = "branch";
  66 }
  67
  68 void Cbranch::evalInstr()
  69 {
  70         this->m_s = argbits[0];
  71         this->m_taken = argbits[1];
  72
  73         argbits >>= 2;
  74
  75         dynamic_bitset<> type = argbits;
  76         type.resize(2);
  77         this->m_typ = type.to_ulong();
  78
  79         switch(this->m_typ) {
  80                 case 0:
  81                         this->name = "br";
  82                         break;
  83                 case 1:
  84                         this->name = "call";
  85                         break;
  86                 case 2:
  87                         this->name = "ret";
  88                         this->clockcount = 3;
  89                         break;
  90                 case 3:
  91                         this->name = "reti";
  92                         this->clockcount = 3;
  93                         break;
  94                 default:
  95                         cerr << "What have you done? 2 bits that have more than 4 values?!" << endl;
  96         }
  97
  98         argbits >>= 5;
  99
 100         dynamic_bitset<> immb = argbits;
 101         immb.resize(16);
 102         this->m_imm = this->generate16ImmSign(immb.to_ulong())*4;
 103
 104 }
 105
 106 void Cbranch::execInstr()
 107 {
 108         //cout << "should exec " << this->toString() << endl;
 109         CDat pc = this->m_cpu->getCurPC();
 110         switch(this->m_typ) {
 111                 case 1:
 112                         {
 113                         CDat sp = this->m_cpu->getStack();
 114                         sp -= 4;
 115                         this->m_cpu->setRAM(sp, this->m_cpu->getNextPC());
 116                         this->m_cpu->setStack(sp);
 117                         }
 118                         /* fall through */
 119                 case 0:
 120                         this->m_cpu->setNextPC(pc+(this->m_imm));
 121                         break;
 122                 case 2:
 123                 case 3:
 124                         this->m_cpu->setNextPC(this->m_cpu->getRAM(this->m_cpu->getStack()));
 125                         this->m_cpu->setStack(this->m_cpu->getStack()+4);
 126                         break;
 127                 default:
 128                         // nothing
 129                         this->m_cpu->setNextPC(400);
 130         }
 131 }
 132
 133 std::string Cbranch::toString()
 134 {
 135         stringstream op;
 136         op << this->getName();
 137
 138         if(m_s) op << 'S';
 139
 140         op << this->getConditionFlag() << (m_taken ? '+' : '-');
 141         if(m_typ < 2) {
 142                 op << " 0x" << std::hex << m_imm << "(" << std::dec << m_imm << ", " << (int) m_imm << ")";
 143         }
 144         return op.str();
 145 }