README
^^^^^^
This README discusses issues unique to NuttX configurations for the
Atmel SAM4S Xplained development board. This board features the
ATSAM4S16C MCU with 1MB FLASH and 128KB.
The SAM4S Xplained features:
- 120 MHz Cortex-M4 with MPU
- 12MHz crystal (no 32.768KHz crystal)
- Segger J-Link JTAG emulator on-board for program and debug
- MICRO USB A/B connector for USB connectivity
- IS66WV51216DBLL ISSI SRAM 8Mb 512K x 16 55ns PSRAM 2.5v-3.6v
- Four Atmel QTouch buttons
- External voltage input
- Four LEDs, two controllable from software
- Xplained expansion headers
- Footprint for external serial Flash (not fitted)
Contents
^^^^^^^^
- PIO Muliplexing
- Development Environment
- GNU Toolchain Options
- IDEs
- NuttX EABI "buildroot" Toolchain
- NuttX OABI "buildroot" Toolchain
- NXFLAT Toolchain
- Buttons and LEDs
- Serial Consoles
- SAM4S Xplained-specific Configuration Options
- Configurations
PIO Muliplexing
^^^^^^^^^^^^^^^
PA0 SMC_A17 PB0 J2.3 default PC0 SMC_D0
PA1 SMC_A18 PB1 J2.4 PC1 SMC_D1
PA2 J3.7 default PB2 J1.3 & J4.3 PC2 SMC_D2
PA3 J1.1 & J4.1 PB3 J1.4 & J4.4 PC3 SMC_D3
PA4 J1.2 & J4.2 PB4 JTAG PC4 SMC_D4
PA5 User_button BP2 PB5 JTAG PC5 SMC_D5
PA6 J3.7 optional PB6 JTAG PC6 SMC_D6
PA7 CLK_32K PB7 JTAG PC7 SMC_D7
PA8 CLK_32K PB8 CLK_12M PC8 SMC_NWE
PA9 RX_UART0 PB9 CLK_12M PC9 Power on detect
PA10 TX_UART0 PB10 USB_DDM PC10 User LED D9
PA11 J3.2 default PB11 USB_DDP PC11 SMC_NRD
PA12 MISO PB12 ERASE PC12 J2.2
PA13 MOSI PB13 J2.3 optional PC13 J2.7
PA14 SPCK PB14 N/A PC14 SMC_NCS0
PA15 J3.5 PC15 SMC_NSC1
PA16 J3.6 PC16 N/A
PA17 J2.5 PC17 User LED D10
PA18 J3.4 & SMC_A14 PC18 SMC_A0
PA19 J3.4 optional & SMC_A15 PC19 SMC_A1
PA20 J3.1 & SMC_A16 PC20 SMC_A2
PA21 J2.6 PC21 SMC_A3
PA22 J2.1 PC22 SMC_A4
PA23 J3.3 PC23 SMC_A5
PA24 TSLIDR_SL_SN PC24 SMC_A6
PA25 TSLIDR_SL_SNSK PC25 SMC_A7
PA26 TSLIDR_SM_SNS PC26 SMC_A8
PA27 TSLIDR_SM_SNSK PC27 SMC_A9
PA28 TSLIDR_SR_SNS PC28 SMC_A10
PA29 TSLIDR_SR_SNSK PC29 SMC_A11
PA30 J4.5 PC30 SMC_A12
PA31 J1.5 PC31 SMC_A13
Development Environment
^^^^^^^^^^^^^^^^^^^^^^^
Several possibile development enviorments may be use:
- Linux or OSX native
- Cygwin unders Windows
- MinGW + MSYS under Windows
- Windows native (with GNUMake from GNUWin32).
All testing has been performed using Cygwin under Windows.
The source has been built only using the GNU toolchain (see below). Other
toolchains will likely cause problems.
GNU Toolchain Options
^^^^^^^^^^^^^^^^^^^^^
The NuttX make system has been modified to support the several different
toolchain options.
All testing has been conducted using the NuttX buildroot toolchain. To use
the CodeSourcery, devkitARM or Raisonance GNU toolchain, you simply need to
add one of the following configuration options to your .config (or defconfig)
file:
CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYW=y : CodeSourcery under Windows
CONFIG_ARMV7M_TOOLCHAIN_CODESOURCERYL=y : CodeSourcery under Linux
CONFIG_ARMV7M_TOOLCHAIN_ATOLLIC=y : Atollic toolchain for Windos
CONFIG_ARMV7M_TOOLCHAIN_DEVKITARM=y : devkitARM under Windows
CONFIG_ARMV7M_TOOLCHAIN_BUILDROOT=y : NuttX buildroot under Linux or Cygwin (default)
CONFIG_ARMV7M_TOOLCHAIN_GNU_EABIL=y : Generic GCC ARM EABI toolchain for Linux
CONFIG_ARMV7M_TOOLCHAIN_GNU_EABIW=y : Generic GCC ARM EABI toolchain for Windows
If you are not using CONFIG_ARMV7M_TOOLCHAIN_BUILDROOT, then you may also
have to modify the PATH in the setenv.h file if your make cannot find the
tools.
NOTE about Windows native toolchains
------------------------------------
The CodeSourcery (for Windows), Atollic, and devkitARM toolchains are
Windows native toolchains. The CodeSourcery (for Linux), NuttX buildroot,
and, perhaps, the generic GCC toolchains are Cygwin and/or Linux native
toolchains. There are several limitations to using a Windows based
toolchain in a Cygwin environment. The three biggest are:
1. The Windows toolchain cannot follow Cygwin paths. Path conversions are
performed automatically in the Cygwin makefiles using the 'cygpath' utility
but you might easily find some new path problems. If so, check out 'cygpath -w'
2. Windows toolchains cannot follow Cygwin symbolic links. Many symbolic links
are used in Nuttx (e.g., include/arch). The make system works around these
problems for the Windows tools by copying directories instead of linking them.
But this can also cause some confusion for you: For example, you may edit
a file in a "linked" directory and find that your changes had no effect.
That is because you are building the copy of the file in the "fake" symbolic
directory. If you use a Windows toolchain, you should get in the habit of
making like this:
make clean_context all
An alias in your .bashrc file might make that less painful.
3. Dependencies are not made when using Windows versions of the GCC. This is
because the dependencies are generated using Windows pathes which do not
work with the Cygwin make.
MKDEP = $(TOPDIR)/tools/mknulldeps.sh
NOTE 1: Older CodeSourcery toolchains (2009q1) do not work with default
optimization level of -Os (See Make.defs). It will work with -O0, -O1, or
-O2, but not with -Os.
NOTE 2: The devkitARM toolchain includes a version of MSYS make. Make sure that
the paths to Cygwin's /bin and /usr/bin directories appear BEFORE the devkitARM
path or will get the wrong version of make.
IDEs
^^^^
NuttX is built using command-line make. It can be used with an IDE, but some
effort will be required to create the project (There is a simple RIDE project
in the RIDE subdirectory).
Makefile Build
--------------
Under Eclipse, it is pretty easy to set up an "empty makefile project" and
simply use the NuttX makefile to build the system. That is almost for free
under Linux. Under Windows, you will need to set up the "Cygwin GCC" empty
makefile project in order to work with Windows (Google for "Eclipse Cygwin" -
there is a lot of help on the internet).
Native Build
------------
Here are a few tips before you start that effort:
1) Select the toolchain that you will be using in your .config file
2) Start the NuttX build at least one time from the Cygwin command line
before trying to create your project. This is necessary to create
certain auto-generated files and directories that will be needed.
3) Set up include pathes: You will need include/, arch/arm/src/sam34,
arch/arm/src/common, arch/arm/src/armv7-m, and sched/.
4) All assembly files need to have the definition option -D __ASSEMBLY__
on the command line.
Startup files will probably cause you some headaches. The NuttX startup file
is arch/arm/src/sam34/sam_vectors.S. You may need to build NuttX
one time from the Cygwin command line in order to obtain the pre-built
startup object needed by RIDE.
NuttX EABI "buildroot" Toolchain
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
A GNU GCC-based toolchain is assumed. The files */setenv.sh should
be modified to point to the correct path to the Cortex-M3 GCC toolchain (if
different from the default in your PATH variable).
If you have no Cortex-M3 toolchain, one can be downloaded from the NuttX
SourceForge download site (https://sourceforge.net/projects/nuttx/files/buildroot/).
This GNU toolchain builds and executes in the Linux or Cygwin environment.
1. You must have already configured Nuttx in <some-dir>/nuttx.
cd tools
./configure.shsam4s-xplained/<sub-dir>
2. Download the latest buildroot package into <some-dir>
3. unpack the buildroot tarball. The resulting directory may
have versioning information on it like buildroot-x.y.z. If so,
rename <some-dir>/buildroot-x.y.z to <some-dir>/buildroot.
4. cd <some-dir>/buildroot
5. cp configs/cortexm3-eabi-defconfig-4.6.3 .config
6. make oldconfig
7. make
8. Edit setenv.h, if necessary, so that the PATH variable includes
the path to the newly built binaries.
See the file configs/README.txt in the buildroot source tree. That has more
details PLUS some special instructions that you will need to follow if you are
building a Cortex-M3 toolchain for Cygwin under Windows.
NOTE: Unfortunately, the 4.6.3 EABI toolchain is not compatible with the
the NXFLAT tools. See the top-level TODO file (under "Binary loaders") for
more information about this problem. If you plan to use NXFLAT, please do not
use the GCC 4.6.3 EABI toochain; instead use the GCC 4.3.3 OABI toolchain.
See instructions below.
NuttX OABI "buildroot" Toolchain
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The older, OABI buildroot toolchain is also available. To use the OABI
toolchain:
1. When building the buildroot toolchain, either (1) modify the cortexm3-eabi-defconfig-4.6.3
configuration to use EABI (using 'make menuconfig'), or (2) use an exising OABI
configuration such as cortexm3-defconfig-4.3.3
2. Modify the Make.defs file to use the OABI conventions:
+CROSSDEV = arm-nuttx-elf-
+ARCHCPUFLAGS = -mtune=cortex-m3 -march=armv7-m -mfloat-abi=soft
+NXFLATLDFLAGS2 = $(NXFLATLDFLAGS1) -T$(TOPDIR)/binfmt/libnxflat/gnu-nxflat-gotoff.ld -no-check-sections
-CROSSDEV = arm-nuttx-eabi-
-ARCHCPUFLAGS = -mcpu=cortex-m3 -mthumb -mfloat-abi=soft
-NXFLATLDFLAGS2 = $(NXFLATLDFLAGS1) -T$(TOPDIR)/binfmt/libnxflat/gnu-nxflat-pcrel.ld -no-check-sections
NXFLAT Toolchain
^^^^^^^^^^^^^^^^
If you are *not* using the NuttX buildroot toolchain and you want to use
the NXFLAT tools, then you will still have to build a portion of the buildroot
tools -- just the NXFLAT tools. The buildroot with the NXFLAT tools can
be downloaded from the NuttX SourceForge download site
(https://sourceforge.net/projects/nuttx/files/).
This GNU toolchain builds and executes in the Linux or Cygwin environment.
1. You must have already configured Nuttx in <some-dir>/nuttx.
cd tools
./configure.sh sam4s-xplained/<sub-dir>
2. Download the latest buildroot package into <some-dir>
3. unpack the buildroot tarball. The resulting directory may
have versioning information on it like buildroot-x.y.z. If so,
rename <some-dir>/buildroot-x.y.z to <some-dir>/buildroot.
4. cd <some-dir>/buildroot
5. cp configs/cortexm3-defconfig-nxflat .config
6. make oldconfig
7. make
8. Edit setenv.h, if necessary, so that the PATH variable includes
the path to the newly builtNXFLAT binaries.
Buttons and LEDs
^^^^^^^^^^^^^^^^
Buttons
-------
The SAM4S Xplained has two mechanical buttons. One button is the RESET button
connected to the SAM4S reset line and the other is a generic user configurable
button labeled BP2 and connected to GPIO PA5. When a button is pressed it
will drive the I/O line to GND.
LEDs
----
There are four LEDs on board the SAM4X Xplained board, two of these can be
controlled by software in the SAM4S:
LED GPIO
---------------- -----
D9 Yellow LED PC10
D10 Yellow LED PC17
Both can be illuminated by driving the GPIO output to ground (low).
These LEDs are not used by the board port unless CONFIG_ARCH_LEDS is
defined. In that case, the usage by the board port is defined in
include/board.h and src/sam_leds.c. The LEDs are used to encode OS-related
events as follows:
SYMBOL Meaning LED state
D9 D10
------------------- ----------------------- -------- --------
LED_STARTED NuttX has been started OFF OFF
LED_HEAPALLOCATE Heap has been allocated OFF OFF
LED_IRQSENABLED Interrupts enabled OFF OFF
LED_STACKCREATED Idle stack created ON OFF
LED_INIRQ In an interrupt No change
LED_SIGNAL In a signal handler No change
LED_ASSERTION An assertion failed No change
LED_PANIC The system has crashed OFF Blinking
LED_IDLE MCU is is sleep mode Not used
Thus if D9 is statically on, NuttX has successfully booted and is,
apparently, running normmally. If D10 is flashing at approximately
2Hz, then a fatal error has been detected and the system has halted.
Serial Consoles
^^^^^^^^^^^^^^^
UART1
-----
If you have a TTL to RS-232 convertor then this is the most convenient
serial console to use. UART1 is the default in all of these
configurations.
UART1 RXD PB2 J1 pin 3 J4 pin 3
UART1 TXD PB3 J1 pin 4 J4 pin 4
GND J1 pin 9 J4 pin 9
Vdd J1 pin 10 J4 pin 10
USART1
------
USART1 is another option:
USART1 RXD PA21 J2 pin 6
USART1 TXD PA22 J2 pin 1
GND J2 pin 9
Vdd J2 pin 10
Virtual COM Port
----------------
Yet another option is to use UART0 and the virtual COM port. This
option may be more convenient for long term development, but was
painful to use during board bring-up.
The SAM4S Xplained contains an Embedded Debugger (EDBG) that can be
used to program and debug the ATSAM4S16C using Serial Wire Debug (SWD).
The Embedded debugger also include a Virtual Com port interface over
USART1. Virtual COM port connections:
AT91SAM4S16 ATSAM3U4CAU
-------------- --------------
PA9 RX_UART0 PA9_4S PA12
PA10 TX_UART0 RX_3U PA11
SAM4S Xplained-specific Configuration Options
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
CONFIG_ARCH - Identifies the arch/ subdirectory. This should
be set to:
CONFIG_ARCH=arm
CONFIG_ARCH_family - For use in C code:
CONFIG_ARCH_ARM=y
CONFIG_ARCH_architecture - For use in C code:
CONFIG_ARCH_CORTEXM4=y
CONFIG_ARCH_CHIP - Identifies the arch/*/chip subdirectory
CONFIG_ARCH_CHIP="sam34"
CONFIG_ARCH_CHIP_name - For use in C code to identify the exact
chip:
CONFIG_ARCH_CHIP_SAM34
CONFIG_ARCH_CHIP_SAM4S
CONFIG_ARCH_CHIP_ATSAM4S16C
CONFIG_ARCH_BOARD - Identifies the configs subdirectory and
hence, the board that supports the particular chip or SoC.
CONFIG_ARCH_BOARD=sam4s-xplained (for the SAM4S Xplained development board)
CONFIG_ARCH_BOARD_name - For use in C code
CONFIG_ARCH_BOARD_SAM4S_XPLAINED=y
CONFIG_ARCH_LOOPSPERMSEC - Must be calibrated for correct operation
of delay loops
CONFIG_ENDIAN_BIG - define if big endian (default is little
endian)
CONFIG_RAM_SIZE - Describes the installed DRAM (SRAM in this case):
CONFIG_RAM_SIZE=0x00008000 (32Kb)
CONFIG_RAM_START - The start address of installed DRAM
CONFIG_RAM_START=0x20000000
CONFIG_ARCH_IRQPRIO - The SAM4S supports interrupt prioritization
CONFIG_ARCH_IRQPRIO=y
CONFIG_ARCH_LEDS - Use LEDs to show state. Unique to boards that
have LEDs
CONFIG_ARCH_INTERRUPTSTACK - This architecture supports an interrupt
stack. If defined, this symbol is the size of the interrupt
stack in bytes. If not defined, the user task stacks will be
used during interrupt handling.
CONFIG_ARCH_STACKDUMP - Do stack dumps after assertions
CONFIG_ARCH_LEDS - Use LEDs to show state. Unique to board architecture.
CONFIG_ARCH_CALIBRATION - Enables some build in instrumentation that
cause a 100 second delay during boot-up. This 100 second delay
serves no purpose other than it allows you to calibratre
CONFIG_ARCH_LOOPSPERMSEC. You simply use a stop watch to measure
the 100 second delay then adjust CONFIG_ARCH_LOOPSPERMSEC until
the delay actually is 100 seconds.
Individual subsystems can be enabled:
CONFIG_SAM34_RTC - Real Time Clock
CONFIG_SAM34_RTT - Real Time Timer
CONFIG_SAM34_WDT - Watchdog Timer
CONFIG_SAM34_UART0 - UART 0
CONFIG_SAM34_UART1 - UART 1
CONFIG_SAM34_SMC - Static Memory Controller
CONFIG_SAM34_USART0 - USART 0
CONFIG_SAM34_USART1 - USART 1
CONFIG_SAM34_HSMCI - High Speed Multimedia Card Interface
CONFIG_SAM34_TWI0 - Two-Wire Interface 0
CONFIG_SAM34_TWI1 - Two-Wire Interface 1
CONFIG_SAM34_SPI0 - Serial Peripheral Interface
CONFIG_SAM34_SSC - Synchronous Serial Controller
CONFIG_SAM34_TC0 - Timer Counter 0
CONFIG_SAM34_TC1 - Timer Counter 1
CONFIG_SAM34_TC2 - Timer Counter 2
CONFIG_SAM34_TC3 - Timer Counter 3
CONFIG_SAM34_TC4 - Timer Counter 4
CONFIG_SAM34_TC5 - Timer Counter 5
CONFIG_SAM34_ADC12B - 12-bit Analog To Digital Converter
CONFIG_SAM34_DACC - Digital To Analog Converter
CONFIG_SAM34_PWM - Pulse Width Modulation
CONFIG_SAM34_CRCCU - CRC Calculation Unit
CONFIG_SAM34_ACC - Analog Comparator
CONFIG_SAM34_UDP - USB Device Port
Some subsystems can be configured to operate in different ways. The drivers
need to know how to configure the subsystem.
CONFIG_GPIOA_IRQ
CONFIG_GPIOB_IRQ
CONFIG_GPIOC_IRQ
CONFIG_USART0_ISUART
CONFIG_USART1_ISUART
CONFIG_USART2_ISUART
CONFIG_USART3_ISUART
ST91SAM4S specific device driver settings
CONFIG_U[S]ARTn_SERIAL_CONSOLE - selects the USARTn (n=0,1,2,3) or UART
m (m=4,5) for the console and ttys0 (default is the USART1).
CONFIG_U[S]ARTn_RXBUFSIZE - Characters are buffered as received.
This specific the size of the receive buffer
CONFIG_U[S]ARTn_TXBUFSIZE - Characters are buffered before
being sent. This specific the size of the transmit buffer
CONFIG_U[S]ARTn_BAUD - The configure BAUD of the UART. Must be
CONFIG_U[S]ARTn_BITS - The number of bits. Must be either 7 or 8.
CONFIG_U[S]ARTn_PARTIY - 0=no parity, 1=odd parity, 2=even parity
CONFIG_U[S]ARTn_2STOP - Two stop bits
Configurations
^^^^^^^^^^^^^^
Each SAM4S Xplained configuration is maintained in a sub-directory and
can be selected as follow:
cd tools
./configure.shsam4s-xplained/<subdir>
cd -
. ./setenv.sh
Before sourcing the setenv.sh file above, you should examine it and perform
edits as necessary so that BUILDROOT_BIN is the correct path to the directory
than holds your toolchain binaries.
And then build NuttX by simply typing the following. At the conclusion of
the make, the nuttx binary will reside in an ELF file called, simply, nuttx.
make
The <subdir> that is provided above as an argument to the tools/configure.sh
must be is one of the following.
NOTES:
1. These configurations use the mconf-based configuration tool. To
change any of these configurations using that tool, you should:
a. Build and install the kconfig-mconf tool. See nuttx/README.txt
and misc/tools/
b. Execute 'make menuconfig' in nuttx/ in order to start the
reconfiguration process.
2. Unless stated otherwise, all configurations generate console
output on UART1 which is available on J1 or J4 (see the
section "Serial Consoles" above). USART1 or the virtual COM
port on UART0 are options. The virtual COM port could
be used, for example, by reconfiguring to use UART0 like:
System Type -> AT91SAM3/4 Peripheral Support
CONFIG_SAM_UART0=y
CONFIG_SAM_UART1=n
Device Drivers -> Serial Driver Support -> Serial Console
CONFIG_UART0_SERIAL_CONSOLE=y
Device Drivers -> Serial Driver Support -> UART0 Configuration
CONFIG_UART0_2STOP=0
CONFIG_UART0_BAUD=115200
CONFIG_UART0_BITS=8
CONFIG_UART0_PARITY=0
CONFIG_UART0_RXBUFSIZE=256
CONFIG_UART0_TXBUFSIZE=256
3. Unless otherwise stated, the configurations are setup for
Linux (or any other POSIX environment like Cygwin under Windows):
Build Setup:
CONFIG_HOST_LINUX=y : Linux or other POSIX environment
4. These configurations use the older, OABI, buildroot toolchain. But
that is easily reconfigured:
System Type -> Toolchain:
CONFIG_ARMV7M_TOOLCHAIN_BUILDROOT=y : Buildroot toolchain
CONFIG_ARMV7M_OABI_TOOLCHAIN=y : Older, OABI toolchain
If you want to use the Atmel GCC toolchain, here are the steps to
do so:
Build Setup:
CONFIG_HOST_WINDOWS=y : Windows
CONFIG_HOST_CYGWIN=y : Using Cygwin or other POSIX environment
System Type -> Toolchain:
CONFIG_ARMV7M_TOOLCHAIN_GNU_EABIW=y : General GCC EABI toolchain under windows
This re-configuration should be done before making NuttX or else the
subsequent 'make' will fail. If you have already attempted building
NuttX then you will have to 1) 'make distclean' to remove the old
configuration, 2) 'cd tools; ./configure.sh sam3u-ek/ksnh' to start
with a fresh configuration, and 3) perform the configuration changes
above.
Also, make sure that your PATH variable has the new path to your
Atmel tools. Try 'which arm-none-eabi-gcc' to make sure that you
are selecting the right tool. setenv.sh is available for you to
use to set or PATH variable. The path in the that file may not,
however, be correct for your installation.
See also the "NOTE about Windows native toolchains" in the section call
"GNU Toolchain Options" above.
Configuration sub-directories
-----------------------------
nsh:
This configuration directory will built the NuttShell. See NOTES above.
NOTES:
1. The configuration configuration can be modified to include support
for the on-board SRAM (1MB).
System Type -> External Memory Configuration
CONFIG_SAM34_EXTSRAM0=y : Select SRAM on CS0
CONFIG_SAM34_EXTSRAM0SIZE=1048576 : Size=1MB
Now what are you going to do with the SRAM. There are two choices:
a) To enable the NuttX RAM test that may be used to verify the
external SRAM:
System Type -> External Memory Configuration
CONFIG_SAM34_EXTSRAM0HEAP=n : Don't add to heap
Application Configuration -> System NSH Add-Ons
CONFIG_SYSTEM_RAMTEST=y : Enable the RAM test built-in
In this configuration, the SDRAM is not added to heap and so is
not excessible to the applications. So the RAM test can be
freely executed against the SRAM memory beginning at address
0x6000:0000 (CS0).
nsh> ramtest -h
Usage: <noname> [-w|h|b] <hex-address> <decimal-size>
Where:
<hex-address> starting address of the test.
<decimal-size> number of memory locations (in bytes).
-w Sets the width of a memory location to 32-bits.
-h Sets the width of a memory location to 16-bits (default).
-b Sets the width of a memory location to 8-bits.
To test the entire external SRAM:
nsh> ramtest 60000000 1048576
RAMTest: Marching ones: 60000000 1048576
RAMTest: Marching zeroes: 60000000 1048576
RAMTest: Pattern test: 60000000 1048576 55555555 aaaaaaaa
RAMTest: Pattern test: 60000000 1048576 66666666 99999999
RAMTest: Pattern test: 60000000 1048576 33333333 cccccccc
RAMTest: Address-in-address test: 60000000 1048576
b) To add this RAM to the NuttX heap, you would need to change the
configuration as follows:
System Type -> External Memory Configuration
CONFIG_SAM34_EXTSRAM0HEAP=y : Add external RAM to heap
Memory Management
-CONFIG_MM_REGIONS=1 : Only the internal SRAM
+CONFIG_MM_REGIONS=2 : Also include external SRAM
cbcabe3314