Update README files

configs/arduino-mega2560/README.txt

@@ -1,22 +1,38 @@
 README
 ^^^^^
 
-This is the README file for the port of NuttX to the Arduino Mega 2560 Rev3.
+  This is the README file for the port of NuttX to the Arduino Mega 2560 Rev3.
 
-https://www.arduino.cc/en/Main/ArduinoBoardMega2560
+    https://www.arduino.cc/en/Main/ArduinoBoardMega2560
 
-The board is based on ATMega2560 chip from Atmel
+  The board is based on ATMega2560 chip from Atmel
-
-http://www.atmel.com/devices/atmega2560.aspx
 
+  http://www.atmel.com/devices/atmega2560.aspx
 
 Toolchain
 ^^^^^^^^^
 
-Right now only Atmel's AVR8 Toolchain is supported. You can get it from
+  Right now only Atmel's AVR8 Toolchain is supported. You can get it from
 
-http://www.atmel.com/tools/atmelavrtoolchainforwindows.aspx
+    http://www.atmel.com/tools/atmelavrtoolchainforwindows.aspx
 
-It is basically WinAVR compatible so sub-projects may define WinAVR as a
+  It is basically WinAVR compatible so sub-projects may define WinAVR as a
-tool-chain but specify path to the Atmel AVR8 in path. See
+  tool-chain but specify path to the Atmel AVR8 in path. See
-arduino-mega2560/hello for example.
+  arduino-mega2560/hello for example.
+
+MEMX
+^^^^
+
+  If you use the GCC AVR toolchain from the Atmel Studio, then you can
+  enable suppport for the MEMX storage:
+
+    CONFIG_AVR_HAS_MEMX_PTR=y
+
+  If this support is enabled, then all strings will be saved in FLASH and
+  standard string-oriented interfaces such printf() will change so that
+  they accept memx pointers.
+
+  This means that (1) ALL strings must lie in FLASH, and (2) since the
+  strings are moved from SRAM to FLASH, you will save a LOT of SRAM usage
+  in some configurations that use a lot of string memory (such as the
+  ostest and nsh configurations).

configs/arduino-mega2560/hello/Make.defs

@@ -37,6 +37,12 @@ include ${TOPDIR}/.config
 include ${TOPDIR}/tools/Config.mk
 include ${TOPDIR}/arch/avr/src/avr/Toolchain.defs
 
+ifeq ($(CONFIG_AVR_HAS_MEMX_PTR),y)
+  LDSCRIPT = memx.ld
+else
+  LDSCRIPT = nomemx.ld
+endif
+
 ifeq ($(WINTOOL),y)
   # Windows-native toolchains
   DIRLINK = $(TOPDIR)/tools/copydir.sh
@@ -44,13 +50,13 @@ ifeq ($(WINTOOL),y)
   MKDEP = $(TOPDIR)/tools/mknulldeps.sh
   ARCHINCLUDES = -I. -isystem "${shell cygpath -w $(TOPDIR)/include}"
   ARCHXXINCLUDES = $(ARCHINCLUDES) "${shell cygpath -w $(TOPDIR)/include/cxx}"
-  ARCHSCRIPT = -T "${shell cygpath -w $(TOPDIR)/configs/$(CONFIG_ARCH_BOARD)/scripts/nomemx.ld}"
+  ARCHSCRIPT = -T "${shell cygpath -w $(TOPDIR)/configs/$(CONFIG_ARCH_BOARD)/scripts/$(LDSCRIPT)}"
 else
   # Linux/Cygwin-native toolchain 
   MKDEP = $(TOPDIR)/tools/mkdeps.sh
   ARCHINCLUDES = -I. -isystem "$(TOPDIR)/include"
   ARCHXXINCLUDES =  $(ARCHINCLUDES) -isystem "$(TOPDIR)/include/cxx"
-  ARCHSCRIPT = -T$(TOPDIR)/configs/$(CONFIG_ARCH_BOARD)/scripts/nomemx.ld
+  ARCHSCRIPT = -T$(TOPDIR)/configs/$(CONFIG_ARCH_BOARD)/scripts/$(LDSCRIPT)
 endif
 
 CC = $(CROSSDEV)gcc
@@ -72,6 +78,12 @@ endif
 
 ARCHCFLAGS = -fno-builtin
 ARCHCXXFLAGS = -fno-builtin -fno-exceptions
+
+ifeq ($(CONFIG_AVR_HAS_MEMX_PTR),y)
+  ARCHCFLAGS += -fdata-sections
+  ARCHCXXFLAGS += -fdata-sections
+endif
+
 ARCHWARNINGS = -Wall -Wstrict-prototypes -Wshadow -Wundef
 ARCHWARNINGSXX = -Wall -Wshadow -Wundef
 ARCHDEFINES =

configs/teensy-2.0/README.txt

@@ -17,6 +17,7 @@ Contents
   o Windows Native Toolchains
   o NuttX buildroot Toolchain
   o avr-libc
+  o MEMX
   o Teensy++ Configuration Options
   o Configurations
 
@@ -387,6 +388,23 @@ Build Notes:
 
      make install
 
+MEMX
+^^^^
+
+  If you use the GCC AVR toolchain from the Atmel Studio, then you can
+  enable suppport for the MEMX storage:
+
+    CONFIG_AVR_HAS_MEMX_PTR=y
+
+  If this support is enabled, then all strings will be saved in FLASH and
+  standard string-oriented interfaces such printf() will change so that
+  they accept memx pointers.
+
+  This means that (1) ALL strings must lie in FLASH, and (2) since the
+  strings are moved from SRAM to FLASH, you will save a LOT of SRAM usage
+  in some configurations that use a lot of string memory (such as the
+  ostest and nsh configurations).
+
 Teensy++ Configuration Options
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^