AR: Remove Message Registers.

These were first introduced in #728.

Hopefully I got everything.

debug_module.tex

@@ -311,41 +311,6 @@ \section{Halt Groups, Resume Groups, and External Triggers} \label{hrgroups}
 explicitly allowed. In that case it must be possible to discover the groups by
 using \RdmDmcsTwo even if it's not possible to change the configuration.
 
-\section{Message Registers}
-\label{sec:mr}
-
-Message Registers (MRs) are registers that implement fewer features than a
-traditional register. They support just enough features to pass messages back
-and forth.
-
-Only registers whose description explicitly says they may be MRs may be
-implemented as MRs instead of traditional registers. \RdmDataZero through
-\RdmDataEleven may be MRs, used to let the debugger pass arguments to abstract
-commands, and let the DM pass results from abstract commands back. Debuggers
-must not assume that they'll be able to read back a value that they wrote to a
-register that may be an MR.
-
-A traditional dual-ported register contains a single value, which can be
-read/written through both ports. A MR has two ports: PortA and PortB. It
-contains two values: ValueA and ValueB. Only one of these values has defined
-contents at any one time.
-
-\begin{steps}{For an MR:}
-    \item A write to PortA updates ValueA with the written value, and makes
-        ValueB \unspecified.
-    \item A write to PortB updates ValueB with the written value, and makes
-        ValueA \unspecified.
-    \item A read from PortA returns ValueB.
-    \item A read from PortB returns ValueA.
-\end{steps}
-
-\begin{commentary}
-    A regular register can be used to implement an MR. In some FPGAs it is
-    cheaper to trade off storage for muxes, and in that case the storage can be
-    duplicated (one set of bits for sending and one for receiving) to avoid
-    having to implement muxes to read/write data from/to the correct side.
-\end{commentary}
-
 \section{Abstract Commands} \label{abstractcommands}
 
 The DM supports a set of abstract commands, most of which
@@ -375,12 +340,12 @@ \section{Abstract Commands} \label{abstractcommands}
 unavailable, or because they encounter an error during execution.
 
 If the command takes arguments, the debugger
-must write them to the {\tt data} MRs before writing to \RdmCommand. If a
+must write them to the {\tt data} registers before writing to \RdmCommand. If a
 command returns results, the Debug Module must ensure they are placed
-in the {\tt data} MRs before \FdmAbstractcsBusy is cleared.
-Which {\tt data} MRs are used for the arguments is
+in the {\tt data} registers before \FdmAbstractcsBusy is cleared.
+Which {\tt data} registers are used for the arguments is
 described in Table~\ref{tab:datareg}.  In all cases the least-significant word
-is placed in the lowest-numbered {\tt data} MR. The argument width
+is placed in the lowest-numbered {\tt data} register. The argument width
 depends on the command being executed, and is DXLEN where not explicitly
 specified.
 

introduction.tex

@@ -67,8 +67,6 @@ \section{Terminology}
     \item[Minimal RISC-V Debug Specification]
         A subset of the full Debug Specification that allows for very small
         implementations. See Chapter~\ref{chap:dm}.
-    \item[MR]
-        Message Register, described in Section~\ref{sec:mr}.
     \item[NAPOT]
         Naturally Aligned Power-Of-Two.
     \item[NMI]
@@ -216,10 +214,7 @@ \subsubsection{Incompatible Changes During 1.0 Stable}
 called 1.0 stable.}
 \item \FcsrItriggerNmi was moved from \RcsrEtrigger to \RcsrItrigger, and is now
 subject to the mode bits in that trigger.
-\item DM {\tt data} registers are now Message Registers (see
-Section~\ref{sec:mr}). Debuggers must not assume they can read back the same
-value that they wrote, and must not assume that the result of the last abstract
-command is available as argument to the next abstract command. \PR{728}
+\item \PR{728} introduced Message Registers, which were later removed in \PR{878}.
 \item It may not be possible to read the contents of the Program Buffer using
 the {\tt progbuf} registers. \PR{731}
 \end{steps}

xml/abstract_commands.xml

@@ -258,10 +258,6 @@
             {\tt arg1} (which contains the address used) by the number of bytes
             encoded in \FacAccessmemoryAamsize.
 
-            Implementations that allow this bit to be 1 must implement the
-            relevant {\tt data} registers as traditional registers instead of
-            MRs.
-
             Supporting this variant is optional, but highly recommended for
             performance reasons.
         </field>

xml/dm_registers.xml

@@ -394,9 +394,6 @@
             If \FdmHartinfoDataaccess is 1: Number of 32-bit words in the memory map
             dedicated to shadowing the {\tt data} registers.
 
-            If this value is non-zero, then the {tt data} registers must be
-            traditional registers and not MRs.
-
             Since there are at most 12 {\tt data} registers, the value in this
             register must be 12 or smaller.
         </field>
@@ -640,8 +637,7 @@
     </register>
 
     <register name="Abstract Data 0" short="data0" address="0x04">
-        \RdmDataZero through \RdmDataEleven may be Message Registers, whose
-        behavior is described in Section~\ref{sec:mr}. These registers may
+        \RdmDataZero through \RdmDataEleven are registers that may
         be read or changed by abstract commands. \FdmAbstractcsDatacount indicates how many
         of them are implemented, starting at \RdmDataZero, counting up.
         Table~\ref{tab:datareg} shows how abstract commands use these