diff --git a/doc/README.at91-soc b/doc/README.at91-soc
index bed035c..425fc58 100644
--- a/doc/README.at91-soc
+++ b/doc/README.at91-soc
@@ -39,3 +39,26 @@
 3. add new structures for SoC access
 4. Convert arch, driver and boards file to new SoC
 5. remove legacy code, if all boards and drives are ready
+
+ Join AT91 and AT91RM9200 SoC
+==============================
+
+Approximately 95 percent of AT91 and AT91RM9200 SoC parts are the same.
+So, we should use the chance, to join both archs togetter.
+
+To do this follow step needed:
+
+1. change Makefile
+	@$(MKCONFIG) $(@:_config=) arm arm920t board vendor at91rm9200
+  to
+	@$(MKCONFIG) $(@:_config=) arm arm920t board vendor at91
+2. remove CONFIG_AT91_LEGACY in board config
+3. convert boards file to new SoC access
+4. convert or change drivers
+
+To support the joining process, a new SoC dir (at91) has been adding to
+arm920t arch directory. This directory contains files like at91rm9200 dir, but
+uses the new c structure Soc access. The advantage of this is, we don't merge
+old Soc access code and new code while the board are not converted.
+Finally we can delete the whole at91rm9200 dir, if all board support the
+new AT91-SoC access.