From: Andrew Cagney <cagney@redhat.com>
Date: Fri, 16 Jan 1998 01:09:15 +0000 (+0000)
Subject: Document existence of old (gencode) and new (igen) MIPS ISA simulators.
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=13151a934d9acf7f376225d758d48af42ca4d8c6;p=binutils-gdb.git

Document existence of old (gencode) and new (igen) MIPS ISA simulators.
---

diff --git a/sim/mips/README.Cygnus b/sim/mips/README.Cygnus
index 06c5e433830..5b646eff794 100644
--- a/sim/mips/README.Cygnus
+++ b/sim/mips/README.Cygnus
@@ -1,3 +1,42 @@
+This directory contains two very different simulators:
+
+	o	gencode (old)
+
+		Gencode.c outputs a single monolithic file that is
+		#included by interp.c
+
+	o	igen (new)
+
+		The *.igen files are used as inputs to ../igen/igen.
+		A number of separate, fairly modula files, are created.
+
+The new simulator has a number of advantages:
+
+	o	builtin support for multi-simming (single simulator
+		image supporting a number of different instruction
+		set architectures).
+
+	o	Easier maintenance. The input files are not confused
+		by an intermixing with the generator code.
+
+gencode continues to exist so that old architectures can be emulated.
+*.igen should be used when adding new architectures or adding
+instructions to an existing ISA.
+
+Known bugs?
+
+A mips16 simulator cannot be built using igen.  A custom mips16
+engine.c needs to be written.
+
+In mips.igen, the semantics for many of the instructions were created
+using code generated by gencode.  Those semantic segments could be
+greatly simplified.
+
+
+----
+
+Old README.Cygnus ...
+
 > README.Cygnus
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