Working through issues with the psill logic.

2025-02-11 06:05:49 +00:00 · 2023-10-31 18:50:13 -05:00 · 2023-10-31 18:50:13 -05:00 · b5ecae2056
commit b5ecae2056
parent 53bcb45844
4 changed files with 124 additions and 103 deletions
--- a/src/lsu/align.sv
+++ b/src/lsu/align.sv
@ -68,14 +68,25 @@ module align import cvw::*;  #(parameter cvw_t P) (
  logic [P.LLEN*2-1:0] ReadDataWordSpillAllM;
  logic [P.LLEN*2-1:0] ReadDataWordSpillShiftedM;

-  ////////////////////////////////////////////////////////////////////////////////////////////////////
-  // PC logic 
-  ////////////////////////////////////////////////////////////////////////////////////////////////////
-  
  localparam LLENINBYTES = P.LLEN/8;
  logic [P.XLEN-1:0]     IEUAdrIncrementM;
+  logic [3:0]            IncrementAmount;
+
+  logic [(P.LLEN-1)*2/8:0] ByteMaskSaveM;
+  logic [(P.LLEN-1)*2/8:0] ByteMaskMuxM;
+
+  always_comb begin
+    case(MemRWM)
+      2'b00: IncrementAmount = 4'd0;
+      2'b01: IncrementAmount = 4'd1;
+      2'b10: IncrementAmount = 4'd3;
+      2'b11: IncrementAmount = 4'd7;
+      default: IncrementAmount = 4'd7;
+    endcase
+  end
  /* verilator lint_off WIDTHEXPAND */
-  assign IEUAdrIncrementM = IEUAdrM + LLENINBYTES;
+  //assign IEUAdrIncrementM = IEUAdrM + LLENINBYTES;
+  assign IEUAdrIncrementM = IEUAdrM + IncrementAmount;
  /* verilator lint_on WIDTHEXPAND */
  mux2 #(P.XLEN) ieuadrspillemux(.d0(IEUAdrE), .d1(IEUAdrIncrementM), .s(SelSpillE), .y(IEUAdrSpillE));
  mux2 #(P.XLEN) ieuadrspillmmux(.d0(IEUAdrM), .d1(IEUAdrIncrementM), .s(SelSpillM), .y(IEUAdrSpillM));
@ -88,15 +99,16 @@ module align import cvw::*;  #(parameter cvw_t P) (
  // 1) operation size
  // 2) offset
  // 3) access location within the cacheline
-  logic [$clog2(P.DCACHE_LINELENINBITS/8)-1:$clog2(LLENINBYTES)] WordOffsetM;
+  localparam OFFSET_BIT_POS =  $clog2(P.DCACHE_LINELENINBITS/8);
+  logic [OFFSET_BIT_POS-1:$clog2(LLENINBYTES)] WordOffsetM;
  logic [$clog2(LLENINBYTES)-1:0]                 ByteOffsetM;
  logic                                HalfSpillM, WordSpillM;
-  assign {WordOffsetM, ByteOffsetM} = IEUAdrM[$clog2(P.DCACHE_LINELENINBITS/8)-1:0];
-  assign HalfSpillM = (WordOffsetM == '1) & Funct3M[1:0] == 2'b01 & ByteOffsetM[0] != 1'b0;
-  assign WordSpillM = (WordOffsetM == '1) & Funct3M[1:0] == 2'b10 & ByteOffsetM[1:0] != 2'b00;
+  assign {WordOffsetM, ByteOffsetM} = IEUAdrM[OFFSET_BIT_POS-1:0];
+  assign HalfSpillM = (IEUAdrM[OFFSET_BIT_POS-1:0] == '1) & Funct3M[1:0] == 2'b01;
+  assign WordSpillM = (IEUAdrM[OFFSET_BIT_POS-1:1] == '1) & Funct3M[1:0] == 2'b10;
  if(P.LLEN == 64) begin
    logic DoubleSpillM;
-    assign DoubleSpillM = (WordOffsetM == '1) & Funct3M[1:0] == 2'b11 & ByteOffsetM[2:0] != 3'b00;
+    assign DoubleSpillM = (IEUAdrM[OFFSET_BIT_POS-1:2] == '1) & Funct3M[1:0] == 2'b11;
    assign SpillM = (|MemRWM) & CacheableM & (HalfSpillM | WordSpillM | DoubleSpillM);
  end else begin
    assign SpillM = (|MemRWM) & CacheableM & (HalfSpillM | WordSpillM);
@ -154,10 +166,18 @@ module align import cvw::*;  #(parameter cvw_t P) (
  // write path. Also has the 8:1 shifter muxing for the byteoffset
  // then it also has the mux to select when a spill occurs
  logic [P.LLEN*2-1:0] LSUWriteDataShiftedM;
-  assign LSUWriteDataShiftedM = {LSUWriteDataM, LSUWriteDataM} << (MisalignedM ? 8 * ByteOffsetM : '0);
-  mux2 #(2*P.LLEN) writedataspillmux(LSUWriteDataShiftedM, {{{P.LLEN}{1'b0}}, LSUWriteDataShiftedM[P.LLEN*2-1:P.LLEN]}, SelSpillM, LSUWriteDataSpillM);
-  logic [P.LLEN*2/8-1:0] ByteMaskShiftedM;
-  assign ByteMaskShiftedM = {ByteMaskExtendedM, ByteMaskM};
-  mux2 #(2*P.LLEN/8) bytemaskspillmux(ByteMaskShiftedM, {{{P.LLEN/8}{1'b0}}, ByteMaskExtendedM}, SelSpillM, ByteMaskSpillM);
+  logic [P.LLEN*3-1:0] LSUWriteDataShiftedExtM;  // *** RT: Find a better way.  I've extending in both directions so we don't shift in zeros.  The cache expects the writedata to not have any zero data, but instead replicated data.

+  assign LSUWriteDataShiftedExtM = {LSUWriteDataM, LSUWriteDataM, LSUWriteDataM} << (MisalignedM ? 8 * ByteOffsetM : '0);
+  assign LSUWriteDataShiftedM = LSUWriteDataShiftedExtM[P.LLEN*3-1:P.LLEN];
+  assign LSUWriteDataSpillM = LSUWriteDataShiftedM;
+  //mux2 #(2*P.LLEN) writedataspillmux(LSUWriteDataShiftedM, {LSUWriteDataShiftedM[P.LLEN*2-1:P.LLEN], LSUWriteDataShiftedM[P.LLEN*2-1:P.LLEN]}, SelSpillM, LSUWriteDataSpillM);
+
+  logic [P.LLEN*2/8-1:0] ByteMaskShiftedM;
+  assign ByteMaskShiftedM = ByteMaskMuxM;
+  mux3 #(2*P.LLEN/8) bytemaskspillmux(ByteMaskShiftedM, {{{P.LLEN/8}{1'b0}}, ByteMaskM}, 
+                                      {{{P.LLEN/8}{1'b0}}, ByteMaskMuxM[P.LLEN*2/8-1:P.LLEN/8]}, {SelSpillM, SelSpillE}, ByteMaskSpillM);
+
+  flopenr #(P.LLEN*2/8) bytemaskreg(clk, reset, SelSpillE, {ByteMaskExtendedM, ByteMaskM}, ByteMaskSaveM);
+  mux2 #(P.LLEN*2/8) bytemasksavemux({ByteMaskExtendedM, ByteMaskM}, ByteMaskSaveM, SelSpillM, ByteMaskMuxM);
 endmodule
--- a/src/lsu/lsu.sv
+++ b/src/lsu/lsu.sv
@ -297,7 +297,7 @@ module lsu import cvw::*;  #(parameter cvw_t P) (
      
      cache #(.P(P), .PA_BITS(P.PA_BITS), .XLEN(P.XLEN), .LINELEN(P.DCACHE_LINELENINBITS), .NUMLINES(P.DCACHE_WAYSIZEINBYTES*8/LINELEN),
              .NUMWAYS(P.DCACHE_NUMWAYS), .LOGBWPL(LLENLOGBWPL), .WORDLEN(CACHEWORDLEN), .MUXINTERVAL(P.LLEN), .READ_ONLY_CACHE(0)) dcache(
-        .clk, .reset, .Stall(GatedStallW), .SelBusBeat, .FlushStage(FlushW | IgnoreRequestTLB), .CacheRW(CacheRWM), .CacheAtomic(CacheAtomicM),
+        .clk, .reset, .Stall(GatedStallW & ~SelSpillE), .SelBusBeat, .FlushStage(FlushW | IgnoreRequestTLB), .CacheRW(CacheRWM), .CacheAtomic(CacheAtomicM),
        .FlushCache(FlushDCache), .NextSet(IEUAdrExtE[11:0]), .PAdr(PAdrM), 
        .ByteMask(ByteMaskSpillM), .BeatCount(BeatCount[AHBWLOGBWPL-1:AHBWLOGBWPL-LLENLOGBWPL]),
        .CacheWriteData(LSUWriteDataSpillM), .SelHPTW,
--- a/tests/wally-riscv-arch-test/riscv-test-suite/rv64i_m/privilege/references/WALLY-misaligned-access-01.reference_output
+++ b/tests/wally-riscv-arch-test/riscv-test-suite/rv64i_m/privilege/references/WALLY-misaligned-access-01.reference_output
@ -62,38 +62,39 @@
 77767574
 7b7a7978
 7f7e7d7c
-04030201 # Half1DstData
-08070605
-0c0b0a09
-100f0e0d
-14130211
-18171615
-1c1b1a19
-201f1e1d
-24232221
-28272625
-2c2b2a29
-302f2e2d
-34330231
-38373635
-3c3b3a39
-403f3e3d
-44434241
-48474645
-4c4b4a49
-504f4e4d
-54530251
-58575655
-5c5b5a59
-605f5e5d
-64636261
-68676665
-6c6b6a69
-706f6e6d
-74730271
-78777675
-7c7b7a79
-de7f7e7d
+020100ef # Half1DstData
+06050403
+0a090807
+0e0d0c0b
+0211100f
+16151413
+1a191817
+1e1d1c1b
+2221201f
+26252423
+2a292827
+2e2d2c2b
+0231302f
+36353433
+3a393837
+3e3d3c3b
+4241403f
+46454443
+4a494847
+4e4d4c4b
+0251504f
+56555453
+5a595857
+5e5d5c5b
+6261605f
+66656463
+6a696867
+6e6d6c6b
+0271706f
+76757473
+7a797877
+7e7d7c7b
+7fdeadbe
 03020100 # Word0DstData
 07060504
 0b0a0908
--- a/tests/wally-riscv-arch-test/riscv-test-suite/rv64i_m/privilege/src/WALLY-misaligned-access-01.S
+++ b/tests/wally-riscv-arch-test/riscv-test-suite/rv64i_m/privilege/src/WALLY-misaligned-access-01.S
@ -66,14 +66,14 @@ TEST_HALF0:
        jal ra, CheckAllWriteSignature

 TEST_HALF1:
-        la a0, SourceData+1
-        la a1, Half1DstData
+        la a0, SourceData
+        la a1, Half1DstData+1
        li a2, 16
        jal ra, memcpy8_2
        
        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+1
-        la a1, Half1DstData
+        la a0, SourceData
+        la a1, Half1DstData+1
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
@ -90,38 +90,38 @@ TEST_WORD0:
        jal ra, CheckAllWriteSignature
 	
 TEST_WORD1:
-        la a0, SourceData+1
-        la a1, Word1DstData
+        la a0, SourceData
+        la a1, Word1DstData+1
        li a2, 16
        jal ra, memcpy8_4
 	
        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+1
-        la a1, Word1DstData
+        la a0, SourceData
+        la a1, Word1DstData+1
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
 TEST_WORD2:
-        la a0, SourceData+2
-        la a1, Word2DstData
+        la a0, SourceData
+        la a1, Word2DstData+2
        li a2, 16
        jal ra, memcpy8_4
 	
        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+2
-        la a1, Word2DstData
+        la a0, SourceData
+        la a1, Word2DstData+2
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
 TEST_WORD3:
-        la a0, SourceData+3
-        la a1, Word3DstData
+        la a0, SourceData
+        la a1, Word3DstData+3
        li a2, 16
        jal ra, memcpy8_4

        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+3
-        la a1, Word3DstData
+        la a0, SourceData
+        la a1, Word3DstData+3
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
@ -138,86 +138,86 @@ TEST_DOUBLE0:
        jal ra, CheckAllWriteSignature
 	
 TEST_DOUBLE1:
-        la a0, SourceData+1
-        la a1, Double1DstData
+        la a0, SourceData
+        la a1, Double1DstData+1
        li a2, 16
        jal ra, memcpy8_8
 	
        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+1
-        la a1, Double1DstData
+        la a0, SourceData
+        la a1, Double1DstData+1
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
 TEST_DOUBLE2:
-        la a0, SourceData+2
-        la a1, Double2DstData
+        la a0, SourceData
+        la a1, Double2DstData+2
        li a2, 16
        jal ra, memcpy8_8

        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+2
-        la a1, Double2DstData
+        la a0, SourceData
+        la a1, Double2DstData+2
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
 TEST_DOUBLE3:
-        la a0, SourceData+3
-        la a1, Double3DstData
+        la a0, SourceData
+        la a1, Double3DstData+3
        li a2, 16
        jal ra, memcpy8_8

        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+3
-        la a1, Double3DstData
+        la a0, SourceData
+        la a1, Double3DstData+3
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
 TEST_DOUBLE4:
-        la a0, SourceData+4
-        la a1, Double4DstData
+        la a0, SourceData
+        la a1, Double4DstData+4
        li a2, 16
        jal ra, memcpy8_8
        
        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+4
-        la a1, Double4DstData
+        la a0, SourceData
+        la a1, Double4DstData+4
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
 TEST_DOUBLE5:
-        la a0, SourceData+5
-        la a1, Double5DstData
+        la a0, SourceData
+        la a1, Double5DstData+5
        li a2, 16
        jal ra, memcpy8_8
        
        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+5
-        la a1, Double5DstData
+        la a0, SourceData
+        la a1, Double5DstData+5
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
 TEST_DOUBLE6:
-        la a0, SourceData+6
-        la a1, Double6DstData
+        la a0, SourceData
+        la a1, Double6DstData+6
        li a2, 16
        jal ra, memcpy8_8
 	
        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+6
-        la a1, Double6DstData
+        la a0, SourceData
+        la a1, Double6DstData+6
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
 TEST_DOUBLE7:
-        la a0, SourceData+7
-        la a1, Double7DstData
+        la a0, SourceData
+        la a1, Double7DstData+7
        li a2, 16
        jal ra, memcpy8_8

        # check if the values are write for all sizes and offsets of misaligned loads.
-        la a0, SourceData+7
-        la a1, Double7DstData
+        la a0, SourceData
+        la a1, Double7DstData+7
        li a2, 16
        jal ra, CheckAllWriteSignature
 	
@ -672,7 +672,7 @@ Half1DstData:
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-
+.8byte 0xdeadbeefdeadbeef
 Word0DstData:    
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
@ -684,19 +684,19 @@ Word1DstData:
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-
+.8byte 0xdeadbeefdeadbeef
 Word2DstData:    
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-	
+.8byte 0xdeadbeefdeadbeef	
 Word3DstData:    
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-	
+.8byte 0xdeadbeefdeadbeef	
 Double0DstData:    
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
@ -708,43 +708,43 @@ Double1DstData:
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-	
+.8byte 0xdeadbeefdeadbeef	
 Double2DstData:    
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-	
+.8byte 0xdeadbeefdeadbeef	
 Double3DstData:    
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-	
+.8byte 0xdeadbeefdeadbeef	
 Double4DstData:    
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-	
+.8byte 0xdeadbeefdeadbeef	
 Double5DstData:    
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-	
+.8byte 0xdeadbeefdeadbeef	
 Double6DstData:    
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-	
+.8byte 0xdeadbeefdeadbeef	
 Double7DstData:    
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
 .8byte 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef, 0xdeadbeefdeadbeef
-
+.8byte 0xdeadbeefdeadbeef
 signature:
        .fill 225, 1, 0x00