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)


  - PIO Muliplexing
  - 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

Buttons and LEDs


  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.


  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

  If you have a TTL to RS-232 converter then this is the most convenient
  serial console to use.  UART1 is the default in all of these

    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 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:

  -------------- --------------
  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_family - For use in C code:


  CONFIG_ARCH_architecture - For use in C code:


  CONFIG_ARCH_CHIP - Identifies the arch/*/chip subdirectory


  CONFIG_ARCH_CHIP_name - For use in C code to identify the exact


  CONFIG_ARCH_BOARD - Identifies the boards/ 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_LOOPSPERMSEC - Must be calibrated for correct operation
  of delay loops

  CONFIG_ENDIAN_BIG - define if big endian (default is little

  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_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.

  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.


  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


  Each SAM4S Xplained configuration is maintained in a sub-directory and
  can be selected as follow:


  Before building, make sure the PATH environment variable includes 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.


  The <subdir> that is provided above as an argument to the tools/
  must be is one of the following.


  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
       see additional README.txt files in the NuttX tools repository.

    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

       Device Drivers -> Serial Driver Support -> Serial Console

       Device Drivers -> Serial Driver Support -> UART0 Configuration

  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_ARM_TOOLCHAIN_BUILDROOT=y : Buildroot toolchain
       CONFIG_ARM_TOOLCHAIN_BUILDROOT_OABI=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_ARM_TOOLCHAIN_GNU_EABI=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) 'tools/ sam3u-ek/ksnh' to start
     with a fresh configuration, and 3) perform the configuration changes

     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.

     See also the "NOTE about Windows native toolchains" in the section call
     "GNU Toolchain Options" above.

Configuration sub-directories

    This configuration directory will built the NuttShell.  See NOTES above.

    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_TESTING_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>

           <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