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Some Documentation to fastcpu #99

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merged 2 commits into from
Aug 22, 2015
Merged

Some Documentation to fastcpu #99

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d297f31
Added some documentation to fastcpu
prannoy Aug 22, 2015
e750452
Merge remote-tracking branch 'upstream/master'
prannoy Aug 22, 2015
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55 changes: 45 additions & 10 deletions js/worker/riscv/fastcpu.js
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@ var IsQueueEmpty = foreign.IsQueueEmpty;
var mul = foreign.mul;
var MathAbs = stdlib.Math.abs;

//One of the following error ids are printed to the console in case of an abort()
var ERROR_INCOMPLETE_VMPRIVILEGE = 0;
var ERROR_VMPRIVILEGE = 1;
var ERROR_VMMODE = 2;
Expand All @@ -44,15 +45,18 @@ var ERROR_ERET_PRIV = 10;
var ERROR_MRTS = 11;
var ERROR_ATOMIC_INSTRUCTION = 12;

//Privilege Modes
var PRV_U = 0x00;
var PRV_S = 0x01;
var PRV_H = 0x02;
var PRV_M = 0x03;

//Various operations on the page table
var VM_READ = 0;
var VM_WRITE = 1;
var VM_FETCH = 2;

//Various Causes which need to be written to MCAUSE Register in case of a Trap
var CAUSE_TIMER_INTERRUPT = 0x80000001;
var CAUSE_HOST_INTERRUPT = 0x80000002;
var CAUSE_SOFTWARE_INTERRUPT = 0x80000000;
Expand All @@ -66,7 +70,7 @@ var CAUSE_ENVCALL_SMODE = 0x09;
var CAUSE_ENVCALL_HMODE = 0x0A;
var CAUSE_ENVCALL_MMODE = 0x0B;


//All CSR addresses have been multiplied for implementing in the asm.js way
var CSR_CYCLES = 0x3000;
var CSR_CYCLEW = 0x2400;

Expand Down Expand Up @@ -149,11 +153,24 @@ var CSR_UARCH13 = 0x33334;
var CSR_UARCH14 = 0x33338;
var CSR_UARCH15 = 0x3333C;

/*
Heap Layout
===========
The heap is needed by the asm.js CPU.

0x0 32 CPU registers
0x80 Floating Point Registers
0x2000 CSR Registers
------- RAM --------
0x100000 RAM
*/


var r = new stdlib.Int32Array(heap); // registers
var rp = 0x00; //Never used

var f = new stdlib.Float64Array(heap); // registers
var fp = 0x80;
var fp = 0x80; //Offset to floating point registers in the Heap

var fi = new stdlib.Int32Array(heap); // for copying operations
var fip = 0x80;
Expand All @@ -162,24 +179,27 @@ var ff = new stdlib.Float32Array(heap); // the zero register is used to convert
var ffp = 0x00; //Never used

var csr = new stdlib.Int32Array(heap);
var csrp = 0x2000;
var csrp = 0x2000; //Offset to CSRs in the Heap

var ram = new stdlib.Int32Array(heap);
var ramp = 0x100000;
var ramp = 0x100000; //Offset to Ram in the Heap

var ram8 = new stdlib.Int8Array(heap);
var ram16 = new stdlib.Int16Array(heap);
var ram8 = new stdlib.Int8Array(heap); //8bit view of heap
var ram16 = new stdlib.Int16Array(heap);//16bit view of heap

var pc = 0x200;
var pc = 0x200; //Virutal PC
var pcorigin = 0x200;
var pc_change = 1; //1 implies pc has been changed by an instruction
var ticks = 0;
var amoaddr = 0,amovalue = 0;

var fence = 0x200;
var ppc = 0x200;
var fence = 0x200; //Has the next page address in case of normal operation, it is made equal to ppc in insts like branch, jump etc
var ppc = 0x200; //Physical PC
var ppcorigin = 0x200;


//tlb_index contains the virutal address and tlb_entry will have the correponding Phsysical Address
//If the page number of vaddr matches with the tlb_index then we directly read the tlb_entry to get the Physical Frame Number
var instlb_index = -0x8000; //tlb index for pc
var instlb_entry = -0x8000;
var read8tlb_index = -1; //tlb index for lb ins
Expand Down Expand Up @@ -280,6 +300,7 @@ function ClearInterrupt(line, cpuid) {

function Trap(cause, current_pc) {

//Store the current_pc, set the mcause register and point PC to the Trap Handler
cause = cause|0;
current_pc = current_pc|0;
var current_privilege_level = 0;
Expand Down Expand Up @@ -320,6 +341,7 @@ function MemTrap(addr, op) {

function CheckVMPrivilege(type, op) {

//Checks if the Privilages of a Page Table Entry are being violated
type = type|0;
op = op|0;
var priv = 0;
Expand Down Expand Up @@ -380,6 +402,7 @@ function CheckVMPrivilege(type, op) {

function TranslateVM(addr, op) {

//Converts Virtual Address to Physical Address
addr = addr|0;
op = op|0;
var vm = 0;
Expand Down Expand Up @@ -487,6 +510,7 @@ function TranslateVM(addr, op) {

function SetCSR(addr,value) {

//Handles write to CSR Registers appropriately
addr = addr|0;
value = value|0;
var mask = 0;
Expand Down Expand Up @@ -664,6 +688,7 @@ function SetCSR(addr,value) {

function GetCSR(addr) {

//Handles Read operation on CSR Registers appropriately
addr = addr|0;
var current_privilege_level = 0;
current_privilege_level = (csr[(csrp + CSR_MSTATUS)>>2] & 0x06) >> 1;
Expand Down Expand Up @@ -827,6 +852,7 @@ function GetCSR(addr) {

function IMul(a,b,index) {

//Special Method for 64 Bit Multiplication for Unsigned*Unsigned
a = a|0;
b = b|0;
index = index|0;
Expand Down Expand Up @@ -870,6 +896,7 @@ function IMul(a,b,index) {

function UMul(a,b,index) {

//Special Method for 64 Bit Multiplication for Signed*Signed
a = a|0;
b = b|0;
index = index|0;
Expand Down Expand Up @@ -906,6 +933,7 @@ function UMul(a,b,index) {

function SUMul(a,b,index) {

//Special Method for 64 Bit Multiplication for Signed*Unsigned
a = a|0;
b = b|0;
index = index|0;
Expand Down Expand Up @@ -975,6 +1003,9 @@ function InvalidateTLB(){

function PushPrivilegeStack(){

//0 to 11 bits of mstatus register is considered as the stack.
//Pushing implies just right shifting the 0 to 11 bits by 3 and then setting PRV[1:0] to Machine
//Also set MPRV bit in mstatus register to zero
var mstatus = 0,privilege_level_stack = 0, new_privilege_level_stack = 0;
mstatus = csr[(csrp + CSR_MSTATUS)>>2]|0;
privilege_level_stack = (mstatus & 0xFFF);
Expand All @@ -984,6 +1015,9 @@ function PushPrivilegeStack(){

function PopPrivilegeStack(){

//0 to 11 bits of mstatus register is considered as the stack.
//Pop implies just left shifting the 0 to 11 bits by 3 and then setting PRV3[1:0] to lowest supported privilege mode(User in this case) with IE3 = 1
//Also set MPRV bit in mstatus register to zero
var mstatus = 0,privilege_level_stack = 0, new_privilege_level_stack = 0;
mstatus = csr[(csrp + CSR_MSTATUS)>>2]|0;
privilege_level_stack = (mstatus & 0xFFF);
Expand Down Expand Up @@ -1033,6 +1067,7 @@ function Step(steps, clockspeed) {

case 0x00:
//lb
//If the page number of vaddr matches with the tlb_index then we directly read the tlb_entry to get the Physical Frame Number
if (!((read8tlb_index ^ vaddr) & 0xFFFFF000)) paddr = read8tlb_entry ^ vaddr;
else {

Expand Down Expand Up @@ -2071,7 +2106,7 @@ function Step(steps, clockspeed) {
} else // fence
{

if(!(pc_change|0)) pc = pcorigin + (ppc-ppcorigin)|0;
if(!(pc_change|0)) pc = pcorigin + (ppc-ppcorigin)|0; //pc_change is set to one when pc is calculated in instrctions like branch, jump etc

dsteps = dsteps - ((ppc-ppcorigin) >> 2)|0;
if ((dsteps|0) < 0) {
Expand Down