vsetvl

Vector Set Vector Type and Vector Length

This instruction is defined by:

Encoding

Synopsis

Set the vtype and vl CSRs, and write the new value of vl into rd.

Access

M	HS	U	VS	VU
Always	Always	Always	Always	Always

Always

Decode Variables

Bits<5> xs2 = $encoding[24:20];
Bits<5> xs1 = $encoding[19:15];
Bits<5> xd = $encoding[11:7];

Execution

Pruned, XLEN == 64
Original

XReg new_vtype = X[xs2];
if ((new_vtype[63] == 1'b1) || (new_vtype[5] == 1) || (new_vtype[2:0] == 3'b100)) {
  CSR[vtype].VILL = 1;
  CSR[vtype].VMA = 0;
  CSR[vtype].VTA = 0;
  CSR[vtype].VSEW = 0;
  CSR[vtype].VLMUL = 0;
} else {
  CSR[vtype].VILL = 0;
  CSR[vtype].VMA = new_vtype[7];
  CSR[vtype].VTA = new_vtype[6];
  CSR[vtype].VSEW = new_vtype[5:3];
  CSR[vtype].VLMUL = new_vtype[2:0];
}
VectorState state = vector_state();
XReg vlen = VLEN;
XReg vlmax = (vlen << state.log2_lmul) >> state.log2_sew;
XReg avl = X[xs1];
XReg ceil_avl_over_two = (avl + 1) / 2;
if (avl < vlmax) {
  CSR[vl].VALUE = avl;
} else if (avl < 2 * vlmax) {
  if (RVV_VL_WHEN_AVL_LT_DOUBLE_VLMAX == "ceil(AVL/2)") {
    CSR[vl].VALUE = ceil_avl_over_two;
  } else if (RVV_VL_WHEN_AVL_LT_DOUBLE_VLMAX == "VLMAX") {
    CSR[vl].VALUE = vlmax;
  } else {
    unpredictable("Implementations may choose a custom value for vl in the case AVL < (2*VLMAX), so long as ceil(AVL/2) <= vl <= VLMAX");
  }
} else {
  CSR[vl].VALUE = vlmax;
}
X[xd] = CSR[vl].VALUE;
CSR[vstart].VALUE = 0;

XReg new_vtype = X[xs2];
if ((new_vtype[xlen() - 1] == 1'b1) || new_vtype & 8'd0) != 0) || (new_vtype[5] == 1) || (new_vtype[2:0] == 3'b100) || (xlen() == 32 && new_vtype[2:0] == 3'b101 {
  CSR[vtype].VILL = 1;
  CSR[vtype].VMA = 0;
  CSR[vtype].VTA = 0;
  CSR[vtype].VSEW = 0;
  CSR[vtype].VLMUL = 0;
} else {
  CSR[vtype].VILL = 0;
  CSR[vtype].VMA = new_vtype[7];
  CSR[vtype].VTA = new_vtype[6];
  CSR[vtype].VSEW = new_vtype[5:3];
  CSR[vtype].VLMUL = new_vtype[2:0];
}
VectorState state = vector_state();
XReg vlen = VLEN;
XReg vlmax = (vlen << state.log2_lmul) >> state.log2_sew;
XReg avl = X[xs1];
XReg ceil_avl_over_two = (avl + 1) / 2;
if (avl < vlmax) {
  CSR[vl].VALUE = avl;
} else if (avl < 2 * vlmax) {
  if (RVV_VL_WHEN_AVL_LT_DOUBLE_VLMAX == "ceil(AVL/2)") {
    CSR[vl].VALUE = ceil_avl_over_two;
  } else if (RVV_VL_WHEN_AVL_LT_DOUBLE_VLMAX == "VLMAX") {
    CSR[vl].VALUE = vlmax;
  } else {
    unpredictable("Implementations may choose a custom value for vl in the case AVL < (2*VLMAX), so long as ceil(AVL/2) <= vl <= VLMAX");
  }
} else {
  CSR[vl].VALUE = vlmax;
}
X[xd] = CSR[vl].VALUE;
CSR[vstart].VALUE = 0;