README
======

This README discusses issues unique to NuttX configurations for the
Atmel SAMD20 Xplained Pro development board. This board features the
ATSAMD20J18A MCU.

The SAMD20 Xplained Pro Starter Kit may be bundled with three modules:

1) I/O1 - An MMC/SD card slot, PWM LED control, ADC light sensor, USART
loopback, TWI AT30TSE758 Temperature sensor.
2) OLED1 - An OLED plus 3 additional switches and 3 additional LEDs
3) PROTO1 - A prototyping board with logic on board (other than power-related
logic).

Contents
========

- STATUS/ISSUES
- Modules
- Development Environment
- GNU Toolchain Options
- IDEs
- NuttX EABI "buildroot" Toolchain
- LEDs
- Serial Consoles
- Atmel Studio 6.1
- SAMD20 Xplained Pro-specific Configuration Options
- Configurations

STATUS/ISSUES
=============

1. The FLASH wait states is set to 2 (see include/board.h). According to
the data sheet, it should work at 1 but I sometimes see crashes when
the wait states are set to one (about half of the time) (2014-2-18).

2. Garbage appears on the display sometimes after a reset (maybe 20% of
the time) or after a power cycle (less after a power cycle). I don't
understand the cause of of this but most of this can be eliminated by
simply holding the reset button longer and releasing it cleanly
(then it fails maybe 5-10% of the time, maybe because of button
chatter?) (2014-2-18).

- The garbage is not random: It is always the same.
- This is not effected by BAUD rate. Curiously, the same garbage
appears at different BAUD settings implying that this may not even
be clock related???
- The program seems to be running normally, just producing bad output.

3. SPI current hangs so not much progress has been made testing the I/O1
module. The hang occurs because the SPI is waiting for SYNCBUSY to
be cleared after enabling the SPI. This even does not happen and so
causes the hang.

Another note: Enabling the SPI on SERCOM0 also seems to interfere
with the USART output on SERCOM4. Both symptoms imply some clock-
related issue.

The configuration suggests CONFIG_MMCSD_HAVE_CARDDETECT=y, but as of
this writing, there is no support for EIC pin interrupts.

4. OLED1 module is untested. These instructions were just lifted from
the SAM4L Xplained Pro README.txt file.

Modules
=======

The SAMD20 Xplained Pro Starter Kit is bundled with four modules:

I/O1
----
The primary function of this module is to provide SD card support, but
the full list of modules features include:

- microSD card connector (SPI interface)
- PWM (LED control)
- ADC (light sensor)
- USART loopback
- TWI AT30TSE758 Temperature sensor with EEPROM

SPI is available on two of the SAMD20 Xplained connectors, EXT1 and EXT2.
They mate with the I/O1 connector as indicated in this table.

I/O1 CONNECTOR
----------------- ---------------------- ---------------------- ------------------------------------
I/O1 EXT1 EXT2 Other use of either pin
----------------- ---------------------- ---------------------- ------------------------------------
1 ID 1 1 Communication line to ID chip on
extension board.
----------------- ---------------------- ---------------------- ------------------------------------
2 GND 2 GND 2 GND
----------------- ---------------------- ---------------------- ------------------------------------
3 LIGHTSENSOR 3 PB00 AIN[8] 3 PA10 AIN[18]
----------------- ---------------------- ---------------------- ------------------------------------
4 LP_OUT 4 PB01 AIN[9] 4 PA11 AIN[19]
----------------- ---------------------- ---------------------- ------------------------------------
5 GPIO1 5 PB06 GPIO 5 PA20 GPIO
----------------- ---------------------- ---------------------- ------------------------------------
6 GPIO2 6 PB07 GPIO 6 PA21 GPIO
----------------- ---------------------- ---------------------- ------------------------------------
7 LED 7 PB02 TC6/WO[0] 7 PA22 TC4/WO[0]
----------------- ---------------------- ---------------------- ------------------------------------
8 LP_IN 8 PB03 TC6/WO[1] 8 PA23 TC4/WO[1]
----------------- ---------------------- ---------------------- ------------------------------------
9 TEMP_ALERT 9 PB04 EXTINT[4] 9 PB14 EXTINT[14]
----------------- ---------------------- ---------------------- ------------------------------------
10 microSD_DETECT 10 PB05 GPIO 10 PB15 GPIO
----------------- ---------------------- ---------------------- ------------------------------------
11 TWI SDA 11 PA08 SERCOM2 PAD[0] 11 PA08 SERCOM2 PAD[0] EXT1, EXT2, EXT3 and EDBG
I�C SDA I�C SDA
----------------- ---------------------- ---------------------- ------------------------------------
12 TWI SCL 12 PA09 SERCOM2 PAD[1] 12 PA09 SERCOM2 PAD[1] EXT2, EXT3 and EDBG
I�C SCL I�C SCL
----------------- ---------------------- ---------------------- ------------------------------------
13 USART RX 13 PB09 SERCOM4 PAD[1] 13 PB13 SERCOM4 PAD[1] The SERCOM4 module is shared between
USART RX USART RX EXT1, 2 and 3 USART's, but uses
different pins
----------------- ---------------------- ---------------------- ------------------------------------
14 USART TX 14 PB08 SERCOM4 PAD[0] 14 PB12 SERCOM4 PAD[0] The SERCOM4 module is shared between
USART TX USART TX EXT1, 2 and 3 USART's, but uses
different pins
----------------- ---------------------- ---------------------- ------------------------------------
15 microSD_SS 15 PA05 SERCOM0 PAD[1] 15 PA17 SERCOM1 PAD[1]
SPI SS SPI SS
----------------- ---------------------- ---------------------- ------------------------------------
16 SPI_MOSI 16 PA06 SERCOM0 PAD[2] 16 PA18 SERCOM1 PAD[2]
SPI MOSI SPI MOSI
----------------- ---------------------- ---------------------- ------------------------------------
17 SPI_MISO 17 PA04 SERCOM0 PAD[0] 17 PA16 SERCOM1 PAD[0]
SPI MISO SPI MISO
----------------- ---------------------- ---------------------- ------------------------------------
18 SPI_SCK 18 PA07 SERCOM0 PAD[3] 18 PA19 SERCOM1 PAD[3]
SPI SCK SPI SCK
----------------- ---------------------- ---------------------- ------------------------------------
19 GND 19 GND GND
----------------- ---------------------- ---------------------- ------------------------------------
20 VCC 20 VCC VCC
----------------- ---------------------- ---------------------- ------------------------------------

The mapping between the I/O1 pins and the SD connector are shown in the
following table.

SD Card Connection
------------------
I/O1 SD PIN Description
---- ---- --- -------------------------------------------------
D2 1 Data line 2 (not used)
15 D3 2 Data line 3. Active low chip select, pulled high
16 CMD 3 Command line, connected to SPI_MOSI.
20 VDD 4
18 CLK 5 Clock line, connected to SPI_SCK.
2/19 GND 6
17 D0 7 Data line 0, connected to SPI_MISO.
D1 8 Data line 1 (not used)
10 SW_A 9 Card detect
2/19 SW_B 10 GND

Card Detect
-----------
When a microSD card is put into the connector SW_A and SW_B are short-
circuited. SW_A is connected to the microSD_DETECT signal. To use this
as a card indicator remember to enable internal pullup in the target
device.

GPIOs
-----
So all that is required to connect the SD is configure the SPI

--- ------------------ ---------------------- -------------------------------------
PIN EXT1 EXT2 Description
--- ------------------ ---------------------- -------------------------------------
15 PA05 SERCOM0 PAD[1] 15 PA17 SERCOM1 PAD[1] Active low chip select OUTPUT, pulled
SPI SS SPI SS high on board.
--- ------------------ ---------------------- -------------------------------------
10 PB05 GPIO 10 PB15 GPIO Active low card detect INPUT, must
use internal pull-up.
--- ------------------ ---------------------- -------------------------------------

Configuration Options:
----------------------
CONFIG_SAMD20_XPLAINED_IOMODULE=y : Informs the system that the
I/O1 module is installed
CONFIG_SAMD20_XPLAINED_IOMODULE_EXT1=y : The module is installed in EXT1
CONFIG_SAMD20_XPLAINED_IOMODULE_EXT2=y : The mdoule is installed in EXT2

See the set-up in the discussion of the nsh configuration below for other
required configuration options.

NOTE: As of this writing, only the SD card slot is supported in the I/O1
module.

OLED1
-----
This module provides an OLED plus 3 additional switches and 3 additional
LEDs.

OLED1 CONNECTOR
----------------- ---------------------- ---------------------- ------------------------------------
OLED1 EXT1 EXT2 Other use of either pin
----------------- ---------------------- ---------------------- ------------------------------------
1 ID 1 1 Communication line to ID chip on
extension board.
----------------- ---------------------- ---------------------- ------------------------------------
2 GND 2 GND 2 GND
----------------- ---------------------- ---------------------- ------------------------------------
3 BUTTON2 3 PB00 AIN[8] 3 PA10 AIN[18]
----------------- ---------------------- ---------------------- ------------------------------------
4 BUTTON3 4 PB01 AIN[9] 4 PA11 AIN[19]
----------------- ---------------------- ---------------------- ------------------------------------
5 DATA_CMD_SEL 5 PB06 GPIO 5 PA20 GPIO
----------------- ---------------------- ---------------------- ------------------------------------
6 LED3 6 PB07 GPIO 6 PA21 GPIO
----------------- ---------------------- ---------------------- ------------------------------------
7 LED1 7 PB02 TC6/WO[0] 7 PA22 TC4/WO[0]
----------------- ---------------------- ---------------------- ------------------------------------
8 LED2 8 PB03 TC6/WO[1] 8 PA23 TC4/WO[1]
----------------- ---------------------- ---------------------- ------------------------------------
9 BUTTON1 9 PB04 EXTINT[4] 9 PB14 EXTINT[14]
----------------- ---------------------- ---------------------- ------------------------------------
10 DISPLAY_RESET 10 PB05 GPIO 10 PB15 GPIO
----------------- ---------------------- ---------------------- ------------------------------------
11 N/C 11 PA08 SERCOM2 PAD[0] 11 PA08 SERCOM2 PAD[0] EXT1, EXT2, EXT3 and EDBG
I�C SDA I�C SDA
----------------- ---------------------- ---------------------- ------------------------------------
12 N/C 12 PA09 SERCOM2 PAD[1] 12 PA09 SERCOM2 PAD[1] EXT2, EXT3 and EDBG
I�C SCL I�C SCL
----------------- ---------------------- ---------------------- ------------------------------------
13 N/C 13 PB09 SERCOM4 PAD[1] 13 PB13 SERCOM4 PAD[1] The SERCOM4 module is shared between
USART RX USART RX EXT1, 2 and 3 USART's, but uses
different pins
----------------- ---------------------- ---------------------- ------------------------------------
14 N/C 14 PB08 SERCOM4 PAD[0] 14 PB12 SERCOM4 PAD[0] The SERCOM4 module is shared between
USART TX USART TX EXT1, 2 and 3 USART's, but uses
different pins
----------------- ---------------------- ---------------------- ------------------------------------
15 DISPLAY_SS 15 PA05 SERCOM0 PAD[1] 15 PA17 SERCOM1 PAD[1]
SPI SS SPI SS
----------------- ---------------------- ---------------------- ------------------------------------
16 SPI_MOSI 16 PA06 SERCOM0 PAD[2] 16 PA18 SERCOM1 PAD[2]
SPI MOSI SPI MOSI
----------------- ---------------------- ---------------------- ------------------------------------
17 N/C 17 PA04 SERCOM0 PAD[0] 17 PA16 SERCOM1 PAD[0]
SPI MISO SPI MISO
----------------- ---------------------- ---------------------- ------------------------------------
18 SPI_SCK 18 PA07 SERCOM0 PAD[3] 18 PA19 SERCOM1 PAD[3]
SPI SCK SPI SCK
----------------- ---------------------- ---------------------- ------------------------------------
19 GND 19 GND GND
----------------- ---------------------- ---------------------- ------------------------------------
20 VCC 20 VCC VCC
----------------- ---------------------- ---------------------- ------------------------------------

Configuration Options:
----------------------
CONFIG_SAMD20_XPLAINED_OLED1MODULE=y : Informs the system that the
I/O1 module is installed
CONFIG_SAMD20_XPLAINED_OLED1MODULE_EXT1=y : The module is installed in EXT1
CONFIG_SAMD20_XPLAINED_OLED1MODULE_EXT2=y : The mdoule is installed in EXT2

See the set-up in the discussion of the nsh configuration below for other
required configuration options.

PROTO1
------
A prototyping board with logic on board (other than power-related logic).
There is no built-in support for the PROTO1 module.

Development Environment
=======================

Either Linux or Cygwin on Windows can be used for the development environment.
The source has been built only using the GNU toolchain (see below). Other
toolchains will likely cause problems. Testing was performed using the Cygwin
environment.

GNU Toolchain Options
=====================


The NuttX make system can be configured to support the various different
toolchain options. All testing has been conducted using the NuttX buildroot
toolchain. To use alternative toolchain, you simply need to add change 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

NOTE about Windows native toolchains
------------------------------------

There are basically three kinds of GCC toolchains that can be used:

1. A Linux native toolchain in a Linux environment,
2. The buildroot Cygwin tool chain built in the Cygwin environment,
3. A Windows native toolchain.

There are several limitations to using a Windows based toolchain (#3) 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.

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.

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 an IDE.

NuttX EABI "buildroot" Toolchain
================================

A GNU GCC-based toolchain is assumed. The PATH environment variable should
be modified to point to the correct path to the Cortex-M0 GCC toolchain (if
different from the default in your PATH variable).

If you have no Cortex-M0 toolchain, one can be downloaded from the NuttX
Bitbucket download site (https://bitbucket.org/nuttx/buildroot/downloads/).
This GNU toolchain builds and executes in the Linux or Cygwin environment.

1. You must have already configured Nuttx in /nuttx.

tools/configure.sh samd20-xplained/

2. Download the latest buildroot package into

3. unpack the buildroot tarball. The resulting directory may
have versioning information on it like buildroot-x.y.z. If so,
rename /buildroot-x.y.z to /buildroot.

4. cd /buildroot

5. cp configs/cortexm0-eabi-defconfig-4.6.3 .config

6. make oldconfig

7. make

8. Make sure 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-M0 toolchain for Cygwin under Windows.

LEDs
====

There is one yellow LED available on the SAM D20 Xplained Pro board that
can be turned on and off. The LED can be activated by driving the connected
PA14 I/O line to GND.

When CONFIG_ARCH_LEDS is defined in the NuttX configuration, NuttX will
control the LED as follows:

SYMBOL Meaning LED0
------------------- ----------------------- ------
LED_STARTED NuttX has been started OFF
LED_HEAPALLOCATE Heap has been allocated OFF
LED_IRQSENABLED Interrupts enabled OFF
LED_STACKCREATED Idle stack created ON
LED_INIRQ In an interrupt N/C
LED_SIGNAL In a signal handler N/C
LED_ASSERTION An assertion failed N/C
LED_PANIC The system has crashed FLASH

Thus is LED is statically on, NuttX has successfully booted and is,
apparently, running normally. If LED is flashing at approximately
2Hz, then a fatal error has been detected and the system has halted.

Serial Consoles
===============

SERCOM4
------

SERCOM4 is available on connectors EXT1, EXT2, and EXT3, but using
different PORT pins:

PIN EXT1 EXT2 EXT3 GPIO Function
---- ---- ---- ---- ------------------
13 PB09 PB13 PB11 SERCOM4 / USART RX
14 PB08 PB12 PB12 SERCOM4 / USART TX
19 GND GND GND N/A
20 VCC VCC VCC N/A

There are options available in the NuttX configuration to select which
connector SERCOM4 is on: SAMD20_XPLAINED_USART4_EXTn, where n=1, 2, or 3.

If you have a TTL to RS-232 converter then this is the most convenient
serial console to use (because you don't lose the console device each time
you lose the USB connection). It is the default in all of these
configurations. An option is to use the virtual COM port.

Virtual COM Port
----------------

The SAMD20 Xplained Pro contains an Embedded Debugger (EDBG) that can be
used to program and debug the ATSAMD20J18A using Serial Wire Debug (SWD).
The Embedded debugger also include a Virtual COM port interface over
SERCOM3. Virtual COM port connections:

PA24 SERCOM3 / USART TXD
PA25 SERCOM3 / USART RXD

Atmel Studio 6.1
================

Loading Code into FLASH:
-----------------------

Tools menus: Tools -> Device Programming.

Debugging the NuttX Object File
-------------------------------

1) Rename object file from nutt to nuttx.elf. That is an extension that
will be recognized by the file menu.

2) File menu: File -> Open -> Open object file for debugging

- Select nuttx.elf object file
- Select AT91SAMD20J18
- Select files for symbols as desired
- Select debugger

3) Debug menu: Debug -> Start debugging and break

- This will reload the nuttx.elf file into FLASH

SAMD20 Xplained Pro-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_CORTEXM0=y

CONFIG_ARCH_CHIP - Identifies the arch/*/chip subdirectory

CONFIG_ARCH_CHIP="samd2l2"

CONFIG_ARCH_CHIP_name - For use in C code to identify the exact
chip:

CONFIG_ARCH_CHIP_SAMD2X
CONFIG_ARCH_CHIP_SAMD20
CONFIG_ARCH_CHIP_ATSAMD20J18

CONFIG_ARCH_BOARD - Identifies the configs subdirectory and
hence, the board that supports the particular chip or SoC.

CONFIG_ARCH_BOARD=samd20-xplained (for the SAMD20 Xplained Pro development board)

CONFIG_ARCH_BOARD_name - For use in C code

CONFIG_ARCH_BOARD_SAMD20_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=0x00010000 (64KB)

CONFIG_RAM_START - The start address of installed DRAM

CONFIG_RAM_START=0x20000000

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_SAMD2L2_WDT - Watchdog Timer"
CONFIG_SAMD2L2_RTC - Real Time Counter"
CONFIG_SAMD2L2_NVMCTRL - Non-Volatile Memory Controller"
CONFIG_SAMD2L2_EVSYS - Event System"
CONFIG_SAMD2L2_SERCOM0 - Serial Communication Interface 0"
CONFIG_SAMD2L2_SERCOM1 - Serial Communication Interface 1"
CONFIG_SAMD2L2_SERCOM2 - Serial Communication Interface 2"
CONFIG_SAMD2L2_SERCOM3 - Serial Communication Interface 3"
CONFIG_SAMD2L2_SERCOM4 - Serial Communication Interface 4"
CONFIG_SAMD2L2_SERCOM5 - Serial Communication Interface 5"
CONFIG_SAMD2L2_TC0 - Timer/Counter 0"
CONFIG_SAMD2L2_TC1 - Timer/Counter 1"
CONFIG_SAMD2L2_TC2 - Timer/Counter 2"
CONFIG_SAMD2L2_TC3 - Timer/Counter 3"
CONFIG_SAMD2L2_TC4 - Timer/Counter 4"
CONFIG_SAMD2L2_TC5 - Timer/Counter 5"
CONFIG_SAMD2L2_TC6 - Timer/Counter 6"
CONFIG_SAMD2L2_TC7 - Timer/Counter 6"
CONFIG_SAMD2L2_ADC - Analog-to-Digital Converter"
CONFIG_SAMD2L2_AC - Analog Comparator"
CONFIG_SAMD2L2_DAC - Digital-to-Analog Converter"
CONFIG_SAMD2L2_PTC - Peripheral Touch Controller"

Some subsystems can be configured to operate in different ways. The drivers
need to know how to configure the subsystem.

CONFIG_SAMD2L2_SERCOM0_ISI2C, CONFIG_SAMD2L2_SERCOM0_ISSPI, or CONFIG_SAMD2L2_SERCOM0_ISUSART
CONFIG_SAMD2L2_SERCOM1_ISI2C, CONFIG_SAMD2L2_SERCOM1_ISSPI, or CONFIG_SAMD2L2_SERCOM1_ISUSART
CONFIG_SAMD2L2_SERCOM2_ISI2C, CONFIG_SAMD2L2_SERCOM2_ISSPI, or CONFIG_SAMD2L2_SERCOM2_ISUSART
CONFIG_SAMD2L2_SERCOM3_ISI2C, CONFIG_SAMD2L2_SERCOM3_ISSPI, or CONFIG_SAMD2L2_SERCOM3_ISUSART
CONFIG_SAMD2L2_SERCOM4_ISI2C, CONFIG_SAMD2L2_SERCOM4_ISSPI, or CONFIG_SAMD2L2_SERCOM4_ISUSART
CONFIG_SAMD2L2_SERCOM5_ISI2C, CONFIG_SAMD2L2_SERCOM5_ISSPI, or CONFIG_SAMD2L2_SERCOM5_ISUSART

SAMD20 specific device driver settings

CONFIG_USARTn_SERIAL_CONSOLE - selects the USARTn (n=0,1,2,..5) for the
console and ttys0 (default is the USART4).
CONFIG_USARTn_RXBUFSIZE - Characters are buffered as received.
This specific the size of the receive buffer
CONFIG_USARTn_TXBUFSIZE - Characters are buffered before
being sent. This specific the size of the transmit buffer
CONFIG_USARTn_BAUD - The configure BAUD of the USART. Must be
CONFIG_USARTn_BITS - The number of bits. Must be either 7 or 8.
CONFIG_USARTn_PARTIY - 0=no parity, 1=odd parity, 2=even parity
CONFIG_USARTn_2STOP - Two stop bits

Configurations
==============

Each SAMD20 Xplained Pro configuration is maintained in a sub-directory and
can be selected as follow:

tools/configure.sh samd20-xplained/

Before building, make sure that the PATH environment variable include 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 that is provided above as an argument to the tools/configure.sh
must be is one of the following.

NOTE: 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.

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
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 of on SERCOM4 which is available on EXT1, EXT2, or EXT3 (see
the section "Serial Consoles" above). The virtual COM port could
be used, instead, by reconfiguring to use SERCOM3 instead of
SERCOM4:

System Type -> SAMD/L Peripheral Support
CONFIG_SAMD2L2_SERCOM3=y : Enable one or both
CONFIG_SAMD2L2_SERCOM4=n

Device Drivers -> Serial Driver Support -> Serial Console
CONFIG_USART4_SERIAL_CONSOLE=y : Select only one for the console
CONFIG_USART4_SERIAL_CONSOLE=n

Device Drivers -> Serial Driver Support -> SERCOM3 Configuration
CONFIG_USART3_2STOP=0
CONFIG_USART3_BAUD=115200
CONFIG_USART3_BITS=8
CONFIG_USART3_PARITY=0
CONFIG_USART3_RXBUFSIZE=256
CONFIG_USART3_TXBUFSIZE=256

Device Drivers -> Serial Driver Support -> SERCOM4 Configuration
CONFIG_USART4_2STOP=0
CONFIG_USART4_BAUD=115200
CONFIG_USART4_BITS=8
CONFIG_USART4_PARITY=0
CONFIG_USART4_RXBUFSIZE=256
CONFIG_USART4_TXBUFSIZE=256

Board Selection -> USART4 Connection
CONFIG_SAMD20_XPLAINED_USART4_EXT1=n : Pick on if USART4 used
CONFIG_SAMD20_XPLAINED_USART4_EXT2=n
CONFIG_SAMD20_XPLAINED_USART4_EXT3=y

3. Unless otherwise stated, the configurations are setup for
Cygwin under Windows:

Build Setup:
CONFIG_HOST_WINDOWS=y : Windows Host
CONFIG_WINDOWS_CYGWIN=y : Cygwin environment on windoes

4. These configurations use the CodeSourcery toolchain. But
that is easily reconfigured:

System Type -> Toolchain:
CONFIG_ARMV6M_TOOLCHAIN_CODESOURCERYW=y

Any 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/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.

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

Configuration sub-directories
-----------------------------

nsh:
This configuration directory will built the NuttShell. See NOTES above
and below:

NOTES:

1. This configuration is set up to build on Windows using the Cygwin
environment using the CodeSourcery toolchain. This can be easily
changed as described above under "Configurations."

2. By default, this configuration provides a serial console on SERCOM4
at 115200 8N1 via EXT3:

PIN EXT3 GPIO Function
---- ---- ------------------
13 PB11 SERCOM4 / USART RX
14 PB12 SERCOM4 / USART TX
19 GND N/A
20 VCC N/A

If you would prefer to use the EDBG serial COM port or would prefer
to use SERCOM4 on EXT1 or EXT2, you will need to reconfigure the
SERCOM as described under "Configurations". See also the section
entitled "Serial Consoles" above.

3. NOTE: If you get a compilation error like:

libxx_new.cxx:74:40: error: 'operator new' takes type 'size_t'
('unsigned int') as first parameter [-fper

Sometimes NuttX and your toolchain will disagree on the underlying
type of size_t; sometimes it is an 'unsigned int' and sometimes it is
an 'unsigned long int'. If this error occurs, then you may need to
toggle the value of CONFIG_CXX_NEWLONG.

4. If the I/O1 module is connected to the SAMD20 Xplained Pro, then
support for the SD card slot can be enabled by making the following
changes to the configuration. These changes assume that the I/O1
modules is connected in EXT1. Most of the modifications necessary
to work with the I/O1 in a different connector are obvious.. except
for the selection of SERCOM SPI support:

EXT1: SPI is provided through SERCOM0
EXT2: SPI is provided through SERCOM1
EXT3: SPI is provided through SERCOM5

File Systems:
CONFIG_FS_FAT=y : Enable the FAT file system
CONFIG_FAT_LCNAMES=y : Enable upper/lower case 8.3 file names (Optional, see below)
CONFIG_FAT_LFN=y : Enable long file named (Optional, see below)
CONFIG_FAT_MAXFNAME=32 : Maximum supported file name length

There are issues related to patents that Microsoft holds on FAT long
file name technologies. See the top level COPYING file for further
details.

System Type -> Peripherals:
CONFIG_SAMD2L2_SERCOM0=y : Use SERCOM0 if the I/O is in EXT1
CONFIG_SAMD2L2_SERCOM0_ISSPI=y : Configure SERCOM0 as an SPI master

Device Drivers
CONFIG_SPI=y : Enable SPI support
CONFIG_SPI_EXCHANGE=y : The exchange() method is supported

CONFIG_MMCSD=y : Enable MMC/SD support
CONFIG_MMCSD_NSLOTS=1 : Only one MMC/SD card slot
CONFIG_MMCSD_MULTIBLOCK_DISABLE=n : Should not need to disable multi-block transfers
CONFIG_MMCSD_MMCSUPPORT=n : May interfere with some SD cards
CONFIG_MMCSD_HAVE_CARDDETECT=y : I/O1 module as a card detect GPIO
CONFIG_MMCSD_SPI=y : Use the SPI interface to the MMC/SD card
CONFIG_MMCSD_SPICLOCK=20000000 : This is a guess for the optimal MMC/SD frequency
CONFIG_MMCSD_SPIMODE=0 : Mode 0 is required

Board Selection -> Common Board Options
CONFIG_NSH_MMCSDSLOTNO=0 : Only one MMC/SD slot, slot 0
CONFIG_NSH_MMCSDSPIPORTNO=0 : Use port=0 -> SERCOM0 if the I/O1 is in EXT1

Board Selection -> SAMD20 Xplained Pro Modules
CONFIG_SAMD20_XPLAINED_IOMODULE=y : I/O1 module is connected
CONFIG_SAMD20_XPLAINED_IOMODULE_EXT1=y : I/O1 modules is in EXT1

Application Configuration -> NSH Library
CONFIG_NSH_ARCHINIT=y : Board has architecture-specific initialization

NOTE: If you enable the I/O1 this configuration with SERCOM4 as the
console and with the I/O1 module in EXT1, you *must* remove USART
jumper. Otherwise, you have lookpack on SERCOM4 and NSH will *not*
behave very well (since its outgoing prompts also appear as incoming
commands).

STATUS: As of 2013-6-18, this configuration appears completely
functional. Testing, however, has been very light. Example:

NuttShell (NSH) NuttX-6.34
nsh> mount -t vfat /dev/mmcsd0 /mnt/stuff
nsh> ls /mnt/stuff
/mnt/stuff:
nsh> echo "This is a test" >/mnt/stuff/atest.txt
nsh> ls /mnt/stuff
/mnt/stuff:
atest.txt
nsh> cat /mnt/stuff/atest.txt
This is a test
nsh>

5. If the OLED1 module is connected to the SAMD20 Xplained Pro, then
support for the OLED display can be enabled by making the following
changes to the configuration. These changes assume that the I/O1
modules is connected in EXT1. Most of the modifications necessary
to work with the I/O1 in a different connector are obvious.. except
for the selection of SERCOM SPI support:

EXT1: SPI is provided through SERCOM0
EXT2: SPI is provided through SERCOM1
EXT3: SPI is provided through SERCOM5

System Type -> Peripherals:
CONFIG_SAMD2L2_SERCOM1=y : Use SERCOM1 if the I/O is in EXT2
CONFIG_SAMD2L2_SERCOM1_ISSPI=y : Configure SERCOM1 as an SPI master

Device Drivers -> SPI
CONFIG_SPI=y : Enable SPI support
CONFIG_SPI_EXCHANGE=y : The exchange() method is supported
CONFIG_SPI_CMDDATA=y : CMD/DATA support is required

Device Drivers -> LCDs
CONFIG_LCD=y : Enable LCD support
CONFIG_LCD_MAXCONTRAST=255 : Maximum contrast value
CONFIG_LCD_LANDSCAPE=y : Landscape orientation (see below*)
CONFIG_LCD_UG2832HSWEG04=y : Enable support for the OLED
CONFIG_LCD_SSD1306_SPIMODE=0 : SPI Mode 0
CONFIG_LCD_SSD1306_SPIMODE=3500000 : Pick an SPI frequency

Board Selection -> SAMD20 Xplained Pro Modules
CONFIG_SAMD20_XPLAINED_OLED1MODULE=y : OLED1 module is connected
CONFIG_SAMD20_XPLAINED_OLED1MODULE_EXT2=y : OLED1 modules is in EXT2

The NX graphics subsystem also needs to be configured:

CONFIG_NX=y : Enable graphics support
CONFIG_NX_LCDDRIVER=y : Using an LCD driver
CONFIG_NX_NPLANES=1 : With a single color plane
CONFIG_NX_WRITEONLY=n : You can read from the LCD (see below**)
CONFIG_NX_DISABLE_2BPP=y : Disable all resolutions except 1BPP
CONFIG_NX_DISABLE_4BPP=y
CONFIG_NX_DISABLE_8BPP=y
CONFIG_NX_DISABLE_16BPP=y
CONFIG_NX_DISABLE_24BPP=y
CONFIG_NX_DISABLE_32BPP=y
CONFIG_NX_PACKEDMSFIRST=y : LSB packed first (shouldn't matter)
CONFIG_NXSTART_EXTERNINIT=y : We have board_graphics_setup()
CONFIG_NXTK_BORDERWIDTH=2 : Use a small border
CONFIG_NXTK_DEFAULT_BORDERCOLORS=y : Default border colors
CONFIG_NXFONTS_CHARBITS=7 : 7-bit fonts
CONFIG_NXFONT_SANS17X23B=y : Pick a font (any that will fit)

* This orientation will put the buttons "above" the LCD. The
reverse landscape configuration (CONFIG_LCD_RLANDSCAPE) will
"flip" the display so that the buttons are "below" the LCD.

** The hardware is write only, but the driver maintains a frame buffer
to support read and read-write-modiry operations on the LCD.
Reading from the frame buffer is, however, untested.

Then, in order to use the OLED, you will need to build some kind of
graphics application or use one of the NuttX graphics examples.
Here, for example, is the setup for the graphic "Hello, World!"
example:

CONFIG_EXAMPLES_NXHELLO=y : Enables the example
CONFIG_EXAMPLES_NXHELLO_DEFAULT_COLORS=y : Use default colors (see below *)
CONFIG_EXAMPLES_NXHELLO_DEFAULT_FONT=y : Use the default font
CONFIG_EXAMPLES_NXHELLO_BPP=1 : One bit per pixel
CONFIG_EXAMPLES_NXHELLO_EXTERNINIT=y : Special initialization is required.

* The OLED is monochrome so the only "colors" are blacka nd white.
The default "colors" will give you while text on a black background.
You can override the faults it you want black text on a while background.

NOTE: One issue that I have seen with the NXHello example when
running as an NSH command is that it only works the first time.
So, after you run the 'nxhello' command one time, you will have to
reset the board before you run it again.

This is clearly some issue with initializing, un-initializing, and
then re-initializing. If you want to fix this, patches are quite
welcome.