apply ACPERM rules in order

src/insns/acperm_32bit.adoc

@@ -29,41 +29,38 @@ ACPERM performs the following operations:
 format shown in xref:acperm_bit_field[xrefstyle=short].
 . Calculate the bitwise AND of the bit field with the mask `rs2`.
 . If the AP and <<m_bit>> field in `cs1` could not have been produced by <<ACPERM>> then
-clear all AP permissions and the <<m_bit>>, and skip the next step
+clear all AP permissions, and the <<m_bit>> to {CAP_MODE_VALUE}. Skip the next step.
 . Clear AP permissions as required to meet the rules below.
-. Encode the AP permissions for MXLEN=32 according to <<cap_perms_encoding32>>.
+. Encode the AP permissions for RV32 according to <<cap_perms_encoding32>>.
 . Copy `cs1` to `cd`, and update the AP and SDP fields with the newly calculated versions.
 . Set `cd.tag=0` if `cs1` is sealed or if any reserved fields of `cs1` are set.
-+
-Some combinations of permissions cannot be encoded for MXLEN=32, and are not useful when MXLEN=64.
-These cases are defined to return useful minimal sets of permissions, which may be no permissions.
-+
-NOTE: Future extensions may allow more combinations of permissions, especially for MXLEN=64.
-
-The common rules are:
-
-. <<asr_perm>> cannot be set without <<x_perm>> being set
-.. Clear <<asr_perm>> unless <<x_perm>> is set
-. <<c_perm>> cannot be set without at least one of <<r_perm>> or <<w_perm>> being set.
-.. Clear <<c_perm>> unless <<r_perm>> or <<w_perm>> are set.
-. <<m_bit>> cannot be set without <<x_perm>> being set
-.. Clear <<m_bit>> unless <<x_perm>> is set
-. <<lm_perm>> cannot be set without <<c_perm>> being set
-.. Clear <<lm_perm>> unless <<c_perm>> is set.
-. <<sl_perm>> cannot be set without <<c_perm>> being set
-.. Zero <<sl_perm>> unless <<c_perm>> is set.
-. <<el_perm>> cannot be set without <<c_perm>> being set
-.. Zero <<el_perm>> unless <<c_perm>> is set.
-
-NOTE: The combination of <<x_perm>> clear and <<m_bit>> set is reserved for future extensions.
-
-The MXLEN=32 additional rules are:
-
-. Clear <<asr_perm>> unless _all_ other permissions are set
-. Clear <<c_perm>> and <<x_perm>> if <<r_perm>> is not set
-. Clear <<w_perm>> if <<c_perm>> _is_ set, but <<lm_perm>> _is not_ set.
-. Clear <<x_perm>> if <<x_perm>> and <<r_perm>> are set, and <<c_perm>> and <<w_perm>> are both clear.
-. If removing <<lm_perm>> results in unrepresentable permissions, then set <<r_perm>> and <<c_perm>> only.
+
+The rules from <<acperm_rules>> must be followed when removing permissions.
+
+[#acperm_rules]
+.ACPERM common rules
+[%autowidth,float="center",align="center",cols="3,3,3",options="header"]
+|===
+| Rule            | Permission   | Only valid if
+|  1  (RV32 only) | <<asr_perm>> | All other permissions are set.
+|  2              | <<c_perm>>   | <<r_perm>> or <<w_perm>>
+|  3  (RV32 only) | <<c_perm>>   | <<r_perm>>
+|  4  (RV32 only) | <<x_perm>>   | <<r_perm>>
+|  5  (RV32 only) | <<w_perm>>   | not(<<c_perm>>) or <<lm_perm>>
+|  6  (RV32 only) | <<x_perm>>   | <<w_perm>> or <<c_perm>>
+|  7              | <<el_perm>>  | <<c_perm>> and <<r_perm>>
+|  8              | <<lm_perm>>  | <<c_perm>> and <<r_perm>>
+|  9  (RV32 only) | <<x_perm>>   | <<c_perm>> == <<lm_perm>> == <<el_perm>>
+| 10              | <<sl_perm>>  | <<c_perm>>
+| 11              | <<asr_perm>> | <<x_perm>>
+| 12              | <<m_bit>>    | <<x_perm>>
+|===
+
+The behaviour of currently illegal combinations from <<acperm_rules>> is to clear the permission if invalid (or in the case of <<sl_perm>> set it to 0 (_local_)).
+
+* For RV64 all such combinations may be redefined by future extensions.
+* For the RV32 only rules none of these combinations are possible to meet the encoding requirements for <<cap_perms_encoding32>>, or
+<<cap_perms_encoding_levels32>> if <<cheri_levels_ext,{cheri_levels_ext_name}>> is implemented. In all cases invalid permissions are cleared.
 
 .Capability permissions bit field
 [#acperm_bit_field]