Update Zbkb

Author: jmawet

arch/inst/Zbkb/brev8.yaml

@@ -3,9 +3,9 @@
 $schema: inst_schema.json#
 kind: instruction
 name: brev8
-long_name: No synopsis available.
+long_name: Reverse the bits in each byte of a source register.
 description: |
-  No description available.
+  This instruction reverses the order of the bits in every byte of a register. 
 definedBy:
   anyOf: [B, Zbkb, Zk, Zkn, Zks]
 assembly: xd, xs1
@@ -23,3 +23,12 @@ access:
   vu: always
 data_independent_timing: false
 operation(): |
+  if (implemented?(ExtensionName::B) && (CSR[misa].Zbkb == 1'b0)) {
+    raise (ExceptionCode::IllegalInstruction, mode(), $encoding);
+  }
+
+  result : xlenbits = EXTZ(0b0);
+  foreach (i from 0 to sizeof(xlen) by 8) {
+    result[i+7..i] = reverse_bits_in_byte(X(rs1)[i+7..i]);
+  };
+  X(rd) = result;

arch/inst/Zbkb/unzip.yaml

@@ -3,9 +3,11 @@
 $schema: inst_schema.json#
 kind: instruction
 name: unzip
-long_name: No synopsis available.
+long_name: Inverse of Zip.
 description: |
-  No description available.
+  This instruction gathers bits from the high and low halves of the source word into odd/even bit
+positions in the destination word. It is the inverse of the zip instruction. This instruction is
+available only on RV32.
 definedBy:
   anyOf: [B, Zbkb, Zk, Zkn, Zks]
 assembly: xd, xs1
@@ -24,3 +26,11 @@ access:
 data_independent_timing: false
 base: 32
 operation(): |
+  if (implemented?(ExtensionName::B) && (CSR[misa].Zbkb == 1'b0)) {
+    raise (ExceptionCode::IllegalInstruction, mode(), $encoding);
+  }
+
+  foreach (i from 0 to xlen/2-1) {
+    X(rd)[i] = X(rs1)[2*i]
+    X(rd)[i+xlen/2] = X(rs1)[2*i+1]
+  }

arch/inst/Zbkb/zip.yaml

@@ -3,9 +3,11 @@
 $schema: inst_schema.json#
 kind: instruction
 name: zip
-long_name: No synopsis available.
+long_name: Gather odd and even bits of the source word into upper/lower halves of the destination.
 description: |
-  No description available.
+  This instruction scatters all of the odd and even bits of a source word into the high and low halves
+of a destination word. It is the inverse of the unzip instruction. This instruction is available only on
+RV32.
 definedBy:
   anyOf: [B, Zbkb, Zk, Zkn, Zks]
 assembly: xd, xs1
@@ -24,3 +26,11 @@ access:
 data_independent_timing: false
 base: 32
 operation(): |
+  if (implemented?(ExtensionName::B) && (CSR[misa].Zbkb == 1'b0)) {
+    raise (ExceptionCode::IllegalInstruction, mode(), $encoding);
+  }
+
+  foreach (i from 0 to xlen/2-1) {
+    X(rd)[2*i] = X(rs1)[i]
+    X(rd)[2*i+1] = X(rs1)[i+xlen/2]
+  }