gistfile1.cpp

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>

/* Declare integer datatypes for each number of bits */
typedef uint_least8_t  u8;  typedef int_least8_t  s8;
typedef uint_least16_t u16; typedef int_least16_t s16;
typedef uint_least32_t u32; typedef int_least32_t s32;
typedef uint_least64_t u64; typedef int_least64_t s64;

/* The following data structures provide templated access
 * of different data sizes within a 32-bit integer.
 */
template<unsigned size, typename T=void>
struct MemDataRef
{
    union { u32 value; T alt[4 / sizeof(T)]; } d;
    // Get a reference to the "size" item beginning
    // at byte position "ind" within the 32-bit word.
    // All requests are assumed to be properly aligned.
    T& reffun(unsigned ind) { return d.alt[ind >> (sizeof(T)==2)]; }
};
template<> struct MemDataRef<1,void>: public MemDataRef<0, u8>  { };
template<> struct MemDataRef<2,void>: public MemDataRef<0, u16> { };
template<> struct MemDataRef<4,void>: public MemDataRef<0, u32> { };

/* Declare facilities for detecting and dealing with different byteorder */
#define LITTLE_ENDIAN_HOST 1 /* 1=little endian */
#define LITTLE_ENDIAN_SLAVE 0 /* 0=big endian */
#define CROSS_ENDIAN (LITTLE_ENDIAN_HOST != LITTLE_ENDIAN_SLAVE)

static unsigned SwapBytes(unsigned value, unsigned size)
{
    if(size >= 2) value = ((value & 0xFF00FF00u) >> 8)
                        | ((value & 0x00FF00FFu) << 8);
    if(size >= 4) value = (value >> 16) | (value << 16);
    return value;
}

/* Console I/O (note: there should be terminal emulation here, but
 *              such implementation is skipped here, for brevity) */
# include <conio.h>
static struct
{
    bool Hit() { return kbhit(); }
    unsigned Getc() { int r = getch(); return r ? r : ' '; }
    void Putc(unsigned c) { putchar(c); fflush(stdout); }
} Console;

/* Declare all the devices that we emulate. */

// RAM device is very simple.
template<unsigned size_bytes>
class SDRAM
{
    u32 buffer[size_bytes / 4];
public:
    u32 Read(u32 index) const        { return buffer[index]; }
    void Write(u32 index, u32 value) { buffer[index] = value; }
};

// Xilinx UART lite (serial port), lite version
class XilinxUARTlite
{
    bool ints_enabled, tx_emptied_int_pending, overrun;
    struct { u8 len, pos, fifo[8]; } in; // Input queue
    // List of supported status and control bits
    enum { RXVALID=1, RXFULL=2, TXEMPTY=4, IE=16, OVERRUN=32, RST_RX=2 };
public:
    XilinxUARTlite(): ints_enabled(0), overrun(0), in{0,0,{0}} { }
    u32 Read(u32 index)
    {
        u32 result = TXEMPTY;
        if(ints_enabled) result |= IE;
        if(in.len > 0)   result |= RXVALID;
        if(in.len == 8)  result |= RXFULL;
        if(overrun)     {result |= OVERRUN; overrun=false;}
        if(index<2 && in.len) result = in.fifo[ (in.pos + 8 - in.len--) % 8 ];
        return result;
    }
    void Write(u32 index, u32 value)
    {
        if(index<3) { Console.Putc(value); tx_emptied_int_pending = true; }
        else { ints_enabled = value&IE; if(value&RST_RX) in.pos=in.len=0; }
    }
    bool CheckIRQ()
    {
        // TX interrupt is an edge; RX interrupt is a level.
        if(ints_enabled && (in.len > 0 || tx_emptied_int_pending))
            { tx_emptied_int_pending=false; return true; }
        return false;
    }
    void Input()
    {
        static unsigned counter = 0;
        if(!counter) counter = 2000; else { --counter; return; }
        if(Console.Hit())
        {
            if(in.len >= 8) { overrun = true; return; }
            in.fifo[ in.pos++ % 8 ] = Console.Getc();
            ++in.len;
        }
    }
};

// Xilinx interrupt timer (multi-timer chip)
template<unsigned N>
class XilinxTimer
{
    // List of registers
    enum { TCSR=0, TLR=1, TCR=2 };
    // List of control bits
    enum { UDT=2, ARHT=16, LOAD=32, ENIT=64, ENT=128, TINT=256, ENALL=1024 };
    struct impl
    {
        u32 regs[4];
        void Write(u32 index, u32 value)
        {
            if(index == TCSR)
                { // Setting the TINT bit actually clears it,
                  // otherwise it is preserved.
                  if(value & TINT) value &= ~TINT;
                  else value |= (regs[index] & TINT); }
            regs[index] = value;
        }
        bool CheckIRQ() const { return (regs[TCSR] & (TINT|ENIT)) == (TINT|ENIT); }
        void Tick()
        {
            if(!(regs[TCSR] & ENT)) return; // Timer does nothing unless enabled
            if(regs[TCSR] & LOAD) { regs[TCR] = regs[TLR]; return; }
            u32 previous = regs[TCSR & UDT] ? regs[TCR]-- : regs[TCR]++;
            if( (previous ^ regs[TCR]) == ~u32(0)) // overflow in either direction
            {
                regs[TCSR] |= TINT; // Raise the interrupt flag
                if(regs[TCSR] & ARHT) regs[TCR] = regs[TLR]; // Restart timer
                else                  regs[TCSR] &= ~ENT;    // Stop timer
            }
        }
    } timers[N];
public:
    u32 Read(u32 which, u32 index)
    {
        return timers[which].regs[index];
    }
    void Write(u32 which, u32 index, u32 value)
    {
        timers[which].Write(index, value);
        // Setting the ENALL bit on any of the timers sets ENT on all of them.
        if(value & ENALL) for(auto& t: timers) t.regs[TCSR] |= ENT;
    }
    void Tick()
    {
        for(auto& t: timers) t.Tick();
    }
    bool CheckIRQ() const
    {
        for(const auto& t: timers) if(t.CheckIRQ()) return true;
        return false;
    }
};

// Xilinx OPB Interrupt Controller
class XilinxINTC
{
    // List of registers
    enum { ISR/* List of active IRQs */,
           IPR,
           IER/* List of IRQs that can result in an interrupt */,
           IAR, SIE, CIE, IVR, MER };
    // List of bits
    enum { ME=1, HIE=2 };
    u32 regs[8];
public:
    XilinxINTC(): regs() { }
    u32 Read(u32 index) const
    {
        if(index == IPR) return regs[ISR] & regs[IER];
        if(index == IVR) // Ordinal number of highest triggered interrupt
        {
            for(unsigned i=0; i<32; ++i) if(Read(IPR) & (1<<i)) return i;
            return ~0u;
        }
        return regs[index];
    }
    void Write(u32 index, u32 value)
    {
        switch(index)
        {
            case SIE: regs[IER] |=  value; break; // Atomic set ie.
            case CIE: regs[IER] &= ~value; break; // Atomic clear ie.
            case IAR: regs[ISR] &= ~value; break; // Acknowledge IRQ (so it's no longer raised)
            case ISR: if(!(regs[MER] & HIE))    // If software interrupts are enabled,
            default:       regs[index] = value; // Update the register as indicated.
        }
    }
    bool CheckIRQ()
    {
        return (regs[MER] & ME) && Read(IPR);
    }
    void TriggerIRQ(unsigned irq)
    {
        if(regs[MER] & HIE) // If hardware interrupts are enabled,
            regs[ISR] |= 1 << irq; // set the IRQ level.
    }
};

enum intent { intent_load, intent_store, intent_execute };

class MicroBlazeCPU // Micro-Blaze CPU
{
    enum {
        v_reset  = 0x00,
        v_usr_ex = 0x08,
        v_intr   = 0x10,
        v_brk    = 0x18,
        v_hw_ex  = 0x20
    };

    union reg // MicroBlaze register file
    {
        struct {  // As 32-bit integers
            u32 MSR; // Machine Status Register, i.e. flags
            u32 ESR; // Exception Status Register, i.e. exception flags
            // 32 general purpose registers.  [0] is always zero and cannot be modified.
            u32 r[32];
            // Special purpose registers.
            // See SPR() below for the list of meanings.
            u32 PC, EAR, BTR, SLR, SHR, ZPR, TLBX, PVRs[16];
            union
            {
                struct { u32 LO, HI; u8 TID; } w;
                struct { u32 G:1, M:1, I:1, W:1, ZSEL:4, WR:1,EX:1, RPN:22;
                         // Bits M, I, W are ignored. RPN=Real Page Number
                         u32 filler:4, U0:1, E:1, V:1, SIZE:3, TAG:22;
                         // E=endianess. Page size is 4^SIZE kibibytes.
                       } b;
            } UTLB[64];
            u8 PID;
        };
        struct { // Or broken down to individual bits:
            // MSR bits:
            u32 lsb:1;
            u32 IE :1; // bit 30 (Interrupt Enable)
            u32 C  :1; // bit 29 (carry)
            u32 BIP:1; // bit 28 (Break In Progress)
            u32 FSL:1, ICE:1;
            u32 DZO:1; // bit 25 (Division By Zero)
            u32 DCE:1;
            u32 EE :1; // bit 23 (Exceptions Enabled)
            u32 EIP:1; // bit 22 (Exception In Progress)
            u32 PVR:1; // bit 21 (PVR register set exists)
            u32 UM :1; // bit 20 (1=Privileged instructions are prohibited, 0=Allowed)
            u32 UMS:1; // bit 19 (User Mode Save)
            u32 VM :1; // bit 18 (1=MMU address translation and access protection enabled)
            u32 VMS:1; // bit 17 (Virtual Protected Mode Save)
            u32 res:16;
            u32 CC :1; // bit 0  (carry copy)
            // ESR bits:
            u32 EC: 5;  // Exception cause
             u32 Rx: 5; // Exception specific status: register
             u32 S:  1; // Exception specific status: store
             u32 DIZ:1; // Exception specific status: zone protection
            u32 DS: 1;  // Delay Slot Exception
            u32 filler: 19;
        };

        void PushUVM() { VMS=VM; UMS=UM; VM=0; UM=0; }
        void PopUVM() { VM=VMS; UM=UMS; }
        // SPR: Special Purpose Register access function (read/write)
        void SPR(unsigned index, bool write, u32& param)
        {
            #define r(reg, writeok) /* write or read macro */ \
                if(!writeok && write) break; \
                if(write) reg = param; else param = reg; \
                return
            auto& tlb = UTLB[TLBX&63];
            switch(index) // The registers are numbered as follows:
            {
                case 0x0000: r(PC, 0);   // PC, program counter
                case 0x0001: r(MSR, 1);  // MSR, machine status register (i.e. flags)
                case 0x0003: r(EAR, 0);  // EAR, exception address register
                case 0x0005: r(ESR, 0);  // ESR, exception status register
                case 0x000B: r(BTR, 0);  // BTR, branch target register
                case 0x0800: r(SLR, 1);  // SLR, stack low register
                case 0x0802: r(SHR, 1);  // SHR, stack high register
                case 0x1000: r(PID, 1);  // PID, process identifier register
                case 0x1001: r(ZPR, 1);  // ZPR, zone protection register
                case 0x1002: r(TLBX, 1); // TLBX, translation look-aside buffer index register
                case 0x1003:             // TLBLO, translation look-aside buffer low register
                    r(tlb.w.LO, 1);
                case 0x1004:             // TLBHI, translation look-aside buffer high register
                    if(write)
                      { tlb.w.TID = PID;
                        tlb.w.HI  = param; }
                    else
                      { if(!UM) PID = tlb.w.TID;
                        param = tlb.w.HI; }
                    return;
                case 0x1005:             // TLBSX, translation look-aside buffer search index register
                    if(write)            // Do a TLB search and report the matching TLB index in TLBX.
                      { TLBX = 0x80000000u; // If nothing found, this value remains indicating the miss.
                        TLBfind<intent_load>(param&0xFFFFFC00,
                          [&](unsigned tlbno) -> unsigned { TLBX = tlbno; return 0; } );
                        return; }
            }
            if(index < 0x2000 || write) index = 15; // Fallback to a safe "undefined" slot
            // Access the processor version registers
            if(write) PVRs[index&15] = param; else param = PVRs[index&15];
            #undef r
        }

        /* Virtual memory management unit (MMU) function */
        template<intent rw, typename T>
        unsigned TLBfind(unsigned virt_addr, const T& func) const
        {
            // Cache the last used index for this type of data access
            static unsigned last_matched_index = 0;

            bool UserMode = UM;
            unsigned exception_no = 16+2+4; // Exception for "no tlb"
            for(unsigned vv=0; vv<64; ++vv)
            {
                unsigned v = (last_matched_index + vv) % 64; // Index into TLB array
                auto& tlb = UTLB[v];

                // Skip invalid TLBs
                if(!tlb.b.V) continue;
                // Skip TLB where TID mismatches the PID
                if(tlb.w.TID != 0 && PID != tlb.w.TID) continue;
                unsigned page_bits = 10 + tlb.b.SIZE * 2;
                // Skip TLB where TAG mismatches the given address
                if( u32(virt_addr ^ (tlb.b.TAG<<10)) >> page_bits ) continue;
                unsigned zone_type = (ZPR >> (30 - tlb.b.ZSEL*2)) & 3;
                // Remove the bit indicating "no tlb found" exception
                exception_no &= ~2;
                if(zone_type == 0 && UserMode)          continue; // zone-prohibited access
                // Remove the bit indicating "zone protection" exception
                exception_no &= ~4;
                if(zone_type < (UserMode?3:2)) // Check WR and EX, unless exempted by zone
                {
                    if(rw==intent_store   && !tlb.b.WR) continue; // write access prohibited
                    if(rw==intent_execute && !tlb.b.EX) continue; // execute access prohibited
                }
                if(rw==intent_execute     && tlb.b.G)   continue; // I/O space is guarded from execution
                last_matched_index = v;
                return func(v);
            }
            return exception_no;
        }
    } regs;

public:
    /* List of read/write functions for each 64k page of the memory space */
    struct { u32(*read)(u32); void(*write)(u32,u32); } IOmap[0x10000];

    /* All memory access is routed through this template function. */
    /* It handles reads and writes of different sizes,
     * with or without virtual memory mapping,
     * with or without byte order swaps (reverse).
     */
    template<intent rw=intent_load, unsigned size=4>
    unsigned MemAccess(u32 virt_addr, u32& value, bool reverse=false)
    {
        u32 phys_addr = virt_addr;
        bool    e_bit = false;

        if(regs.VM) // Virtual memory mode? Do TLB lookup.
        {
            unsigned exception = regs.TLBfind<rw>(virt_addr,
                [&](unsigned tlbno) -> unsigned
                {
                    // Map the address using the matching TLB.
                    unsigned page_mask = (1024 << (2 * regs.UTLB[tlbno].b.SIZE)) - 1;
                    phys_addr = (regs.UTLB[tlbno].b.RPN << 10)
                              + (virt_addr & page_mask);
                    e_bit = regs.UTLB[tlbno].b.E;
                    return 0;
                });
            // Produce an exception if the mapping failed (LSB indicates code/data).
            if(exception)
                return exception | (rw==intent_execute);
        }

        // Verify alignment, and produce an exception if the address was not properly aligned
        if(virt_addr % size != 0) return 1 | (size==4 ? 4 : 0);

        // An "E" bit in a TLB reverses the endianess for that page (except in opcode lookups).
        if(rw != intent_execute) reverse ^= e_bit;
        // This macro byteswaps if needed due to host/guest endian differences or the reverse bit.
        auto S = [=](u32 v) -> u32
            { return size>1 && (reverse != CROSS_ENDIAN) ? SwapBytes(v,size) : v; };
        // Read full 32 bits from the memory/device,
        // unless we're going to replace it entirely.
        MemDataRef<size> data;
        if(rw != intent_store || size != 4)
            data.d.value = IOmap[phys_addr/0x10000].read(phys_addr & ~3);
        // Create a reference to the relevant data within the 32 bit word.
        auto& r = data.reffun( (phys_addr & (4-size)) ^ (reverse ? (4-size) : 0) );
        if(rw == intent_store)
        {
            // Write to the relevant data, and commit
            // the entire 32-bit word the memory/device. Byteswap if needed.
            r = S(value);
            IOmap[phys_addr/0x10000].write(phys_addr & ~3, data.d.value);
        }
        else
            value = S(r); // Read the relevant data. Byteswap if needed.
        return 0; // Return "no exception" code
    }

    // This struct records the desired action to happen after instruction execution.
    struct execmode
    {
        unsigned mode:2, type:30, target:32;
        // Modes:
        //   0 = Normally proceed to the next instruction (other fields are ignored)
        //   1 = Jump, right now. (type=type of jump, target=where to jump)
        //   2 = Jump, but first execute one more instruction (delay slot)
        //   3 = Generate an exception, right now
        //       (type   = type of exception,
        //        target = memory address causing the exception)
    };

    // Decode and execute a single instruction.
    execmode ExecuteOne(u32 i, u32 arg2)
    {
        // Decode the operation type and operands from the opcode
        unsigned i_op = (i>>26)&0x3F;  // Operation
        unsigned i_rd = (i>>21)&0x1F;  // Target register index
        u32 RA = regs.r[(i>>16)&0x1F]; // Source register value
        bool imm = i_op & 0x08;        // Category of instruction
        if(!imm) arg2 = regs.r[(i>>11)&0x1F]; // Second operand

        // Exit macros.
        #define Return return execmode{0,0,0}
        // Exit and store v to RD.
        // Note that regs.r[0] is always preserved as zero, even if written to.
        #define ReturnRD(v) do { if(i_rd) regs.r[i_rd] = (v); Return; } while(0)
        // Exit and store v to RD, and set carry to c (evaluated before v, which may depend on carry).
        #define ReturnRDc(v,c) do { bool nc = (c); if(i_rd) regs.r[i_rd] = (v); regs.C = regs.CC = nc; Return; } while(0)
        // Exit and prepare to branch/jump to another memory location
        #define ReturnJmp(target,delayed,type) return execmode{(delayed)?2:1, type, target}
        // Exit and raise an exception, concerning the given address.
        #define ReturnEx(extype, addr) return execmode{3,extype,addr}
        // Exit and raise a MMU exception, setting the exception info appropriately.
        #define ReturnMMUex(extype, ear, write) \
            do { regs.Rx = i_rd; regs.S = write; regs.DIZ = error & 4; \
                 ReturnEx(extype &~ 4, ear); } while(0)

        // Determine which kind of operation it was:
        if(i == 0x00000000) ReturnEx(2,0); // Specially trap this illegal opcode
        #define tr(op) (((op) & 0x07) | (((op) & 0x30) >> 1))
        switch( tr(i_op) )
        {
            // Add and subtract operations: (ADD|RSUB)(I)(K)(C); comparisons: CMP(U)
            case tr(0x06): ReturnRD(  arg2+RA+regs.C                          ); // ADD(I)KC
            case tr(0x07): ReturnRD(  arg2-RA-regs.C                          ); // RSUB(I)KC
            case tr(0x02): ReturnRDc( arg2+RA+regs.C, arg2+RA+regs.C   < arg2 ); // ADD(I)C
            case tr(0x03): ReturnRDc( arg2-RA-regs.C, arg2-RA-regs.C   > arg2 ); // RSUB(I)C
            case tr(0x00): ReturnRDc( arg2+RA,        arg2+RA          < arg2 ); // ADD(I)
            case tr(0x01): ReturnRDc( arg2-RA,        arg2-RA          > arg2 ); // RSUB(I)
            case tr(0x04): ReturnRD(  arg2+RA                                 ); // ADD(I)K
            case tr(0x05): switch(imm?0:(i&0x7FF))
            { case 0:      ReturnRD(  arg2-RA                                 ); // RSUB(I)K
              case 1: ReturnRD((0x7FFFFFFF&(arg2-RA)) | (((s32)arg2 < (s32)RA)<<31) ); // CMP
              case 3: ReturnRD((0x7FFFFFFF&(arg2-RA)) | (((u32)arg2 < (u32)RA)<<31) ); // CMPU
            } Return;/*Silently ignore bad instruction*/

            // Bit manipulation operations: (OR|AND|XOR|ANDN)(I)
            case tr(0x20): ReturnRD( RA |  arg2 ); // OR,  ORI
            case tr(0x21): ReturnRD( RA &  arg2 ); // AND, ANDI
            case tr(0x22): ReturnRD( RA ^  arg2 ); // XOR, XORI
            case tr(0x23): ReturnRD( RA &~ arg2 ); // ANDN,ANDNI
            // Barrel shift operations: BS(RL|RA|LL)(I)
            case tr(0x11):
                if(i&0x400) ReturnRD( RA      << (arg2 & 31) ); // BSLL(I)
                if(i&0x200) ReturnRD( s32(RA) >> (arg2 & 31) ); // BSRA(I)
                else        ReturnRD( u32(RA) >> (arg2 & 31) ); // BSRL(I)
            // Multiplications: MUL(I|H|HU|HSU)
            case tr(0x10): switch(imm ? 0 : (i&0x7FF))
            { case 0: ReturnRD( (s32)RA * (s32)arg2 );                   // MUL,MULI
              case 1: ReturnRD( ((s64)(s32)RA * (s64)(s32)arg2) >> 32 ); // MULH
              case 2: ReturnRD( ((s64)(s32)RA * (s64)(u32)arg2) >> 32 ); // MULHSU
              case 3: ReturnRD( ((u64)(u32)RA * (u64)(u32)arg2) >> 32 ); // MULHU
            } Return;
            // One-bit copy / shift-right operators: SEXT(8|16), SR(A|C|L); cache control: W(I|D)C
            case tr(0x24): switch(i & 0x7FF)
            { case 0x60: ReturnRD( (s32)( s8)RA ); // SEXT8  (sign-extend 8 bits to 32 bits)
              case 0x61: ReturnRD( (s32)(s16)RA ); // SEXT16 (sign-extend 16 bits to 32 bits)
              case 0x01: ReturnRDc(            (s32)RA >> 1,  RA&1); // SRA (sign-extend)
              case 0x21: ReturnRDc((regs.CC<<31) | (RA >> 1), RA&1); // SRC (carry-extend)
              case 0x41: ReturnRDc(                 RA >> 1,  RA&1); // SRL (zero-extend)
              case 0x64: if(regs.UM) ReturnEx(7,0); Return; // WDC
              case 0x66: if(regs.UM) ReturnEx(7,0); Return; // WDC.clear
              case 0x74: if(regs.UM) ReturnEx(7,0); Return; // WDC.flush
              case 0x76: if(regs.UM) ReturnEx(7,0); Return; // WDC.flush.clear
              case 0x68: if(regs.UM) ReturnEx(7,0); Return; // WIC (privileged cache-control instruction)
            } Return;
            // Conditional branches with delay slots or not: (BEQ|BNE|BLT|BLE|BGT|BGE)(I)(D)
            case tr(0x27): switch(i_rd & 15)
            { case 0: if((s32)RA == 0) ReturnJmp( regs.PC-4 + arg2, i_rd & 16, 0 ); Return; //EQ
              case 1: if((s32)RA != 0) ReturnJmp( regs.PC-4 + arg2, i_rd & 16, 0 ); Return; //NE
              case 2: if((s32)RA  < 0) ReturnJmp( regs.PC-4 + arg2, i_rd & 16, 0 ); Return; //LT
              case 3: if((s32)RA <= 0) ReturnJmp( regs.PC-4 + arg2, i_rd & 16, 0 ); Return; //LE
              case 4: if((s32)RA  > 0) ReturnJmp( regs.PC-4 + arg2, i_rd & 16, 0 ); Return; //GT
              case 5: if((s32)RA >= 0) ReturnJmp( regs.PC-4 + arg2, i_rd & 16, 0 ); Return; //GE
            } Return;
            // Unconditional branches / system calls, with delay slots or not: BR(A)(L)(I)(D), BRK(I), MBAR
            case tr(0x26): switch( (i >> 18) & 7) // This is hairy, because there are so many variants in this.
            {
                #define R if(i_rd) regs.r[i_rd] = regs.PC - 4; /* Macro for saving return address */
                case 0:   ReturnJmp(arg2+regs.PC-4, false, 0); // D=0, A=0, L=0 (BR(I) or MBAR).
                case 4:   ReturnJmp(arg2+regs.PC-4, true,  0); // D=1, A=0, L=0 (BR(I)D)
                case 5: R ReturnJmp(arg2+regs.PC-4, true,  0); // D=1, A=0, L=1 (BRL(I)D)
                case 2:   ReturnJmp(arg2,           false, 0); // D=0, A=1, L=0 (BRA(I))
                case 6:   ReturnJmp(arg2,           true,  0); // D=1, A=1, L=0 (BRA(I)D)
                case 7: {bool e = imm && arg2 == v_usr_ex;     // D=1, A=1, L=1 (BRAL(I)D)
                        R ReturnJmp(arg2, true, e ? 3 : 0 );}  //                escalate if target 0x08)
                case 3: {bool e = imm && (arg2 == v_usr_ex || arg2 == v_brk);
                        if(regs.UM && !e) ReturnEx(7,0);       // D=0, A=1, L=1 (BRK(I) = special, not delayed)
                        regs.BIP = true;                       //                deny usermode access, except
                        R ReturnJmp(arg2, false, e ? 3 : 0 );} //                escalate if target 0x08 or 0x18
                case 1: break;                                 // D=0, A=0, L=1 (BRL(I) = invalid)
                #undef R
            } Return;
            // Subroutine/exception returns: RT(S|I|B|E)D; Special register manipulation: M(F|T)S, MSR(CLR|SET)
            case tr(0x25):
                if(imm) // Note: MicroBlaze's return opcodes always include a delay slot.
                {
                    if((i_rd&7) && regs.UM) ReturnEx(7,0); // privileged return
                    ReturnJmp(RA+arg2, true, i_rd&7); // RTSD=0/RTID=1/RTBD=2/RTED=4
                }
                // MFS and MTS
               {u32& op2 = i_rd ? regs.r[i_rd] : arg2;
                if((i&0x4000) && regs.UM) ReturnEx(7,0); // Write is a privileged operation
                regs.SPR( i&0x3FFF, (i&0x4000), (i&0x4000) ? RA : op2 ); // Write or read
                // Update the carry-copy bit
                regs.CC = regs.C;
                regs.PVR = true; // Ensure this flag is never turned off
                ReturnRD(op2);}

            // Memory access operations:
            #define HandleLoadStoreOpcode(opcode, rw, size) \
                case tr(opcode): \
                { \
                    if(auto error = MemAccess<rw,size>(RA+arg2, regs.r[i_rd], !imm && (i&0x200))) \
                        ReturnMMUex(error, RA+arg2, rw==intent_store); \
                    if(rw == intent_load && !i_rd) regs.r[i_rd] = 0; /* Ensure RD stays zero */ \
                    if(!imm && (i&0x400)) regs.C = regs.CC = false; /* exclusive access, not implemented */ \
                    ReturnRD(regs.r[i_rd]); \
                }
            HandleLoadStoreOpcode(0x30, intent_load,1) // LBU(I)(R)
            HandleLoadStoreOpcode(0x31, intent_load,2) // LHU(I)(R)
            HandleLoadStoreOpcode(0x32, intent_load,4) // LW(I)(R)(X)
            HandleLoadStoreOpcode(0x34, intent_store,1) // SB(I)(R)
            HandleLoadStoreOpcode(0x35, intent_store,2) // SH(I)(R)
            HandleLoadStoreOpcode(0x36, intent_store,4) // SW(I)(R)(X)
        }
        #undef tr
        // Anything else: Illegal instruction exception
        ReturnEx(2,0);
    }

    // Reset the CPU
    void DoReset(u32 vector = v_reset, u32 cmdline_pointer = 0)
    {
        // Clear all registers. (Note: Real MicroBlaze does not clear R1..R31.)
        regs = {};
        // Set those registers that should not be zero:
        regs.SHR = 0xFFFFFFFFu;
        regs.PC   = vector;
        regs.r[5] = cmdline_pointer;
        // The following CPU features are not supported by this emulator:
        //
        // C_USE_PCMP_INSTR not implemented (PCMPNE,PCMPEQ,PCMPBF,CLZ) because CLZ and PCMPBF require proportionally much code
        // C_USE_DIV        not implemented (IDIV,IDIVU) because handling the corner cases requires much code
        // C_USE_FPU=1      not implemented (FADD,FRSUB,FMUL,FDIV,FCMP) because lots of code (comparisons, corner cases)
        // C_USE_FPU=2      not implemented (FLT,FINT,FSQRT) because C_USE_FPU=1 not implemented
        // C_USE_STACK_PROTECTION not implemented because not utilized by Linux
        // C_USE_MSR_INSTR  not implemented because implementation takes unproportional amount of code and not really needed
        // C_FSL_LINKS      not implemented because is very complex framework but yet completely ignored by Linux
        //
        // The following CPU features ARE supported by this emulator:
        //
        // C_USE_BARREL=1, because emulating these was cheap in my opinion, and they help the performance a great deal
        // C_USE_HW_MUL=2, because emulating these was cheap in my opinion, and they help the performance a great deal
        // C_ILL_OPCODE_EXCEPTIONS=1, trivial to implement
        // C_UNALIGNED_EXCEPTIONS=1,  trivial to implement
        // C_OPCODE_0x0_ILLEGAL=1,    trivial to implement
        // C_USE_MMU=3,    because without a fully functional MMU, Linux would be quite crippled in my opinion
        // C_MMU_ZONES=16, because once you support one, supporting 16 is trivial. Linux requires at least 2.
        // C_MMU_PRIVILEGED_INSTR=0 fully protect privileged instructions
        // C_MMU_TLB_ACCESS=3 full TLB register access
        //
        // Now, set up bit fields indicating the list of processor features.
        // For brevity (to save time in the video), I use hexadecimal constants here.
        regs.PVR  = true;
        regs.PVRs[0] = 0xD4801500;
        regs.PVRs[2] = 0x00005470;
        regs.PVRs[11] = 0xC0200000|regs.MSR;
    }

    bool InterruptsEnabled() const
    {
        return regs.IE && !regs.EIP && !regs.BIP;
    }
    // Process an interrupt request (note: Call this only when InterruptsEnabled()=true).
    void DoInterrupt(u32 vector = v_intr)
    {
        regs.PushUVM(); // Go to kernel mode, save current mode
        regs.IE    = false;
        regs.r[14] = regs.PC;
        regs.PC    = vector;
    }

    // Fetch and execute one instruction, and process branch/jump/exception
    void Singlestep()
    {
        execmode next;

        auto NextOpcode = [&] (u32& value) -> bool
        {
            unsigned error = MemAccess<intent_execute,4>(regs.PC, value, !CROSS_ENDIAN);
            if(error) { next = {3,error&~4,regs.PC}; return false; } // Exception
            regs.PC += 4;
            return true;
        };

        u32 op_begin = regs.PC;

        u32 opcode;
        if(!NextOpcode(opcode))
        {
            // Loading the instruction failed; produce an exception.
            goto GotException;
        }

        // HACK: When Linux function "emit_log_char" is invoked, output the
        // character directly to the UART. This makes the boot-process more
        // verbose when the kernel UART driver has not been loaded yet.
        if(op_begin == 0xc0010e04) IOmap[0x8400].write(0,regs.r[5]<<24);

       {s32 immval = (s16)opcode;
        // If the opcode was IMM, read the next one immediately.
        if( (opcode >> 16) == 0xB000 )
        {
            if(!NextOpcode(opcode)) goto GotException;
            immval = (immval << 16) | (opcode & 0xFFFF); // Extend the literal parameter
        }
        next = ExecuteOne(opcode, immval);}
        switch(next.mode)
        {
            case 0: default: break;
            case 2: // Delayed jump
            {
                u32 btr = next.target; // Save the branch target
                if(!NextOpcode(opcode)) { next.mode = 2; regs.BTR = btr; goto GotException; }

                // Execute the in-delay-slot instruction.
                // Note: MicroBlaze documentation explictly prohibits the delay
                //       slot being taken by an IMM, BRK or branch instruction,
                //       so we won't deal with those cases here.
                execmode next2 = ExecuteOne(opcode, (s16)opcode);
                if(next2.mode == 3) // Did an exception happen in a delay slot?
                    { regs.BTR    = btr;
                      next.type   = next2.type;   // Copy exception type
                      next.target = next2.target; // Copy exception address
                      goto GotException; }
            } // passthru
            case 1: // Jump
                switch(next.type) // Check for a special type of a jump
                {
                    // type 1 = Return From Interrupt (set IE; copy UMS,VMS to UM,VM)
                    case 1: regs.IE = true; regs.PopUVM(); break;
                    // type 2 = Return From Break (clear BIP; copy UMS,VMS to UM,VM)
                    case 2: regs.BIP = false; regs.PopUVM(); break;
                    // type 3 = Break or User Exception (copy UM,VM to UMS,VMS)
                    case 3: regs.PushUVM(); break;
                    // type 4 = Return From Exception (set EE, clear EIP, zero ESR; copy UMS,VMS to UM,VM)
                    case 4: regs.EIP = false; regs.EE = true; regs.ESR = 0; regs.PopUVM(); break;
                }
                regs.PC = next.target;
                break;
            case 3: GotException:; // Exception
                if(regs.EE || next.type >= 16)
                {
                    // If EE is unset, ignore exception unless caused by MMU
                    // For MMU exceptions, the return address is the beginning
                    // of the opcode that caused the fault. For others, it is
                    // the next opcode.
                    regs.EIP = true;        // Exception in progress = true
                    regs.EAR = next.target; // Address causing the exception
                    regs.EE  = false;       // Exceptions enabled = false
                    regs.EC  = next.type;   // Exception code
                    regs.DS  = next.mode == 2; // Was it a delay slot exception.
                    regs.PushUVM();         // Go kernel mode, save previous mode
                    regs.r[17] = (next.type < 16 ? regs.PC : op_begin);
                    regs.PC = v_hw_ex;
                }
        }
    }
};

// Emulate the following hardware (Linux kernel is configured for them using a DTS):
MicroBlazeCPU  cpu;      // Configured at 100 MHz
SDRAM<0x1800000> RAM;    // IO: 10000000 , 24 MiB of RAM (MicroBlaze Linux requires >=16.)
SDRAM<0x10000> LowRAM;   // IO: 00000000 , 64 KiB of RAM (needed for exception tables)
XilinxINTC        intc;  // IO: 81800000
XilinxTimer<2>    timer; // IO: 83c00000 IRQ 3
XilinxUARTlite    uart;  // IO: 84000000 IRQ 8

// Helper function for swapping byte order on memory access.
static u32 S(u32 v) { return CROSS_ENDIAN ? SwapBytes(v, 4) : v; }

int main()
{
    // Set up the memory mapping.

    // First, make all unassigned addresses produce a run-time error.
    for(unsigned a=0; a<0x10000; ++a)
        cpu.IOmap[a] = { [](u32)->u32{ abort(); },
                         [](u32,u32) { abort(); } };

    cpu.IOmap[0x0000] = { [](u32 i)       { return LowRAM.Read(i/4); } ,
                          [](u32 i,u32 v) { LowRAM.Write(i/4,v); } };
    for(unsigned a=0x1000; a<0x1180; ++a)
        cpu.IOmap[a] = { [](u32 i)       { return RAM.Read((i-0x10000000)/4); } ,
                         [](u32 i,u32 v) { RAM.Write((i-0x10000000)/4,v); } };

    cpu.IOmap[0x8180] = { [](u32 i)       { return S(intc.Read((i/4)%8)); } ,
                          [](u32 i,u32 v) { intc.Write((i/4)%8,S(v)); } };

    cpu.IOmap[0x8400] = { [](u32 i)       { return S(uart.Read((i/4)%4)); } ,
                          [](u32 i,u32 v) { uart.Write((i/4)%4,S(v)); } };

    cpu.IOmap[0x83C0] = { [](u32 i)       { return S(timer.Read((i/16)&1, (i/4)%4)); } ,
                          [](u32 i,u32 v) { timer.Write((i/16)&1, (i/4)%4, S(v)); } };


    // Load Linux kernel from U-Boot image
    struct { u32 a[3], image_size, load_offs, entry_offs, b[10]; } Header;
    const char* kernel = "simple~1.ub"; // simpleImage.emu.ub
    FILE* fp = fopen(kernel, "rb");
    fprintf(stderr, "Loading kernel, %s...\n", kernel);
    fread(&Header, 0x40, 1, fp);
    if(LITTLE_ENDIAN_HOST) Header.load_offs  = SwapBytes(Header.load_offs,  4);
    if(LITTLE_ENDIAN_HOST) Header.entry_offs = SwapBytes(Header.entry_offs, 4);
    if(LITTLE_ENDIAN_HOST) Header.image_size = SwapBytes(Header.image_size, 4);

    // Reset the CPU (and bring memory mapper to user mode)
    cpu.DoReset(Header.entry_offs, Header.load_offs + Header.image_size);

    // Read the kernel image into the RAM
    for(auto offs = Header.load_offs; offs < Header.load_offs + Header.image_size; offs += 4)
    {
        u32 value;
        if(fread(&value, 1, 4, fp) <= 0) break;
        cpu.MemAccess<intent_store,4> (offs, value, CROSS_ENDIAN);
    }
    fclose(fp);
    fprintf(stderr, "Done loading kernel.\n");

    // Run the machine
    for(;;) // Infinite loop
    {
        cpu.Singlestep();

        uart.Input();
        timer.Tick();

        if(timer.CheckIRQ()) intc.TriggerIRQ(3);
        if(cpu.InterruptsEnabled())
        {
            if(uart.CheckIRQ()) intc.TriggerIRQ(8);
            if(intc.CheckIRQ()) cpu.DoInterrupt();
        }
    }
}