Nano River Technologies October 2010

Transcription

1 October 2010 Rev: 1.1 (Oct 2010) Page 1 of 36

2 Table of Contents 1. PRELIMINARIES PACKAGING LIST GETTING HELP INSTALLATION (WINDOWS 2000 AND XP) VIPERBOARD INSTALLER PLUGGING IN THE VIPERBOARD INSTALLATION (LINUX) STEP 1: LIBUSB INSTALLATION STEP 2: VIPERBOARD EXAMPLES AND DOCUMENTATION INSTALLATION INSTALLATION (MACOS) STEP 1: LIBUSB INSTALLATION STEP 2: VIPERBOARD EXAMPLES AND DOCUMENTATION INSTALLATION VIPERBOARD HARDWARE OVERVIEW INTERFACES SPI INTERFACE IIC INTERFACE GPIO PORT A INTERFACE GPIO PORT B INTERFACE ANALOGUE INTERFACE LED INDICATOR GETTING STARTED APPENDIX A : SCHEMATIC Congratulations on the purchase of the from Nano River Technologies! We trust that this board will be a valuable asset in the development or test of your own electronics. development team Rev: 1.1 (Oct 2010) Page 2 of 36

3 ABBREVIATIONS API EEPROM G++ GCC GPIO GPIOA GPIOB GUI I2C IIC IO LED Master NRT Slave SPI USB Application Programming Interface Electrically Erasable Programmable Read Only Memory C++ compiler for Linux (part of GCC) GNU Compiler Collection General Purpose IO GPIO Port A (advanced GPIO interface) GPIO Port B (digital IO interface) Graphical User Interface Inter-Integrated Circuit Inter-Integrated Circuit (same as I2C) Input / Output Light Emitting Diode An interface which supplies the clock like the SPI master or I2C master on An interface which receives the clock like the SPI slave or I2C slave on Serial Peripheral Interface Universal Serial Bus Rev: 1.1 (Oct 2010) Page 3 of 36

4 1. Preliminaries 1.1. Packaging List Your comes standard with the following items. One circuit board assembly One USB cable type A to type B PC software, example applications and documentation for use with this product is available downloadable from our web-site. Rev: 1.1 (Oct 2010) Page 4 of 36

5 1.2. Getting Help Most questions relating to installation and usage of the are available from our web-site. If however you have further questions, then please do not hesitate to contact us via . For any sales related questions, please contact: Rev: 1.1 (Oct 2010) Page 5 of 36

6 2. Installation (Windows 2000 and XP) 2.1. Installer The installer activates from the software download page available from: Rev: 1.1 (Oct 2010) Page 6 of 36

7 The installer starts by downloading all documentation and software examples. Rev: 1.1 (Oct 2010) Page 7 of 36

8 To run the applications without MicroSoft Visual C++ installed the Microsoft Visual C redistribution pack is required. This is installed automatically next. Allow all default directories and file names. Next the open source LibUSB-Win USB driver is installed. Allow all default directories and file names. Rev: 1.1 (Oct 2010) Page 8 of 36

9 At the conclusion of the LibUSB-Win USB driver installation there will be the opportunity to run a test program to ensure it installed properly. Running this is optional. At the conclusion of the driver install, a Readme file will be displayed containing an overview of the product. Rev: 1.1 (Oct 2010) Page 9 of 36

10 2.2. Plugging in the When the driver is installed and the plugged into a USB port for the first time, the Found New Hardware wizard will appear. Select Install from a list or specific location. Select Don t search. I will choose the driver to install. Rev: 1.1 (Oct 2010) Page 10 of 36

11 Navigate to the hard disk. Navigate to the install directory for eg C:\Program Files\Installer_ Rev: 1.1 (Oct 2010) Page 11 of 36

12 The Wizard will then find the driver setup file and start to link to the driver. Installation is then complete. The PC can now talk to a. Rev: 1.1 (Oct 2010) Page 12 of 36

13 3. Installation (Linux) Installation of under Linux consists of two steps. First OpenSource LibUsb for Linux is installed. Secondly the example applications and documentation is installed Step 1: LibUsb Installation LibUsb is an OpenSource USB driver available for usage for commercial applications. The class library will make low level USB calls to LibUsb to implement the desired high level functions available through the API. The LibUsb installation is contained within "libusb tar.gz". Installation consists of the following: a) One should first ensure that GNU g++ is available on the Linux machine. This will be needed during the installation. b) In a working directory untar the file using linux%> gzip -cd libusb tar.gz tar xvf - c) Move to the created directory using linux%> cd libusb d) Run the configure script linux%>./configure e) Run make (become root if necessary) to build LibUsb linux%> make f) Install LibUsb linux%> make install Rev: 1.1 (Oct 2010) Page 13 of 36

14 At this point you should have installed LibUsb for Linux. Unfortunately in most cases it seems that the library can only be seen by the root user. This means that applications would only work as root. To fix this one needs to edit one of the rule files in UDEV. g) Change to be root linux%> sudo bash h) Edit for example your /etc/udev/rules.d/40-basic-permissions.rules to include the following two new lines (in red). This makes the USB connection able to be seen by someone other than root. # USB devices (usbfs replacement) SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", MODE="0664" SUBSYSTEM=="usb_device", MODE="0664" #New lines for Viperboard SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device",SYSFS{idVendor}=="04b4", SYSFS{idProduct}=="1004", MODE="0666" SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device",SYSFS{idVendor}=="2058", SYSFS{idProduct}=="1005", MODE="0666" The above change to permissions shows how to change USB permissions for Ubuntu Linux. For other kernels permissions may need to be changed in other files. For example in Federa 11, one needs to make the modification to /lib/udev/rules.d/50-udev-default.rules. i) You can return from being root now and you are ready to install the examples and documentation. Rev: 1.1 (Oct 2010) Page 14 of 36

15 3.2. Step 2: Examples and Documentation Installation a) Documents and the example applications are all contained in _Installation_1.0.2.tar.gz. Untar this in some suitable place. linux%> tar xvfz _Installation_1.0.2.tar.gz b) Move to the created directory. linux%> cd _Installation_1.0.2 c) You will see the following documents to read: Readme.pdf UserGuide_ver_Nov09.pdf API_ver_Nov09.pdf ApplicationExamples_ver_Nov09.pdf d) You will find the application examples in the Examples/ directory. Read ApplicationExamples_ver_Nov09.pdf to learn about running these. The file structure should appear as below. _Installation_1.0.2/ Examples/ common/ viperboard.h viperboard_class.h viperboard_class.c Header File Class Header File Class C++ File src/ ConfigurationExample.c Main Program (Example 1) scripts/ go_configurationexample Compile Script for Application 1 Readme.pdf UserGuide_ver_Nov09.pdf API_ver_Nov09.pdf ApplicationExamples_ver_Nov09.pdf COPYING_GPL.txt COPYING_LGPL.txt Rev: 1.1 (Oct 2010) Page 15 of 36

16 4. Installation (MacOS) Installation of for MacOS consists of two steps. First OpenSource LibUsb for MacOS is installed. Secondly the example applications and documentation is installed Step 1: LibUsb Installation LibUSB must be first installed under MacOS. The simplest way to achieve this is to make use of the installation already included in MacPorts. First visit the MacPorts installation page: Download the MacPorts installation for your version of MacOS by selecting Snow Leopard, Leopard or Tiger. A.dmg file will be downloaded (it will be called something like MacPorts SnowLeopard.dmg). Click to download your MacOS.dmg! Rev: 1.1 (Oct 2010) Page 16 of 36

17 Double click on the downloaded file to mount it and execute the package file (.pkg) to install it. In a command tool install version of LibUsb using the following command: At this point you should have installed LibUsb for MacOS and you are ready to install the examples and documentation. Rev: 1.1 (Oct 2010) Page 17 of 36

18 4.2. Step 2: Examples and Documentation Installation a) Documents and the example applications are all contained in _Installation_1.0.2.tar.gz which comes from the software downloads page for MacOS. Untar this in some suitable place. macos %> tar xvfz _Installation_1.0.2.tar.gz b) Move to the created directory. macos %> cd _Installation_1.0.2 c) You will see the following documents to read: Readme.pdf UserGuide_ver_Nov09.pdf API_ver_Nov09.pdf ApplicationExamples_ver_Nov09.pdf d) You will find the application examples in the Examples/ directory. Read ApplicationExamples_ver_Nov09.pdf to learn about running these. The file structure should appear as below. _Installation_1.0.2/ Examples/ GCC Examples/ common/ viperboard.h viperboard_class.h viperboard_class.c Header File Class Header File Class C++ File src/ ConfigurationExample.c Main Program (Example 1) scripts/ go_configurationexample Compile Script for Application 1 Cocoa Examples/ Xcode Cocoa Example here Readme.pdf UserGuide_ver_Nov09.pdf API_ver_Nov09.pdf ApplicationExamples_ver_Nov09.pdf COPYING_GPL.txt COPYING_LGPL.txt Rev: 1.1 (Oct 2010) Page 18 of 36

19 5. Hardware 5.1. Overview Pullups Analogue Input A/D Converter FPGA I2C Master/slave SPI Master/slave Flash Low Pass Filter GPIO Port A USB USB Controller GPIO Port B EEPROM Viperboard is built around a Cypress USB controller chip and FPGA. It accepts commands across the USB bus and then translates these into I2C, SPI and GPIO bus protocols as required. Key features of the Viperboard include: high speed SPI master and slave (up to 17 channels) high speed I2C master and slave with optional pull-ups 16 bit GPIO Port A capable of digital I/O, interrupts, PWM optional low pass filtering for 2 GPIO Port A pins for analogue output 16 bit GPIO Port B capable of digital I/O 4 bit analogue input A full schematic for the Viperboard can be seen in Appendix A. Rev: 1.1 (Oct 2010) Page 19 of 36

20 5.2. Interfaces Separate connectors are provided for each of the I2C, SPI, GPIO and Analogue interfaces. With pins as specified in the following diagrams. GPIO Ports A/B J2-A J2-B X2 SPI Interface X3 J3 U2 U1 X4 Not Used No jumper! IIC Interface J1-A J1-B X5 D2 X1 Analog Interface USB Interface Rev: 1.1 (Oct 2010) Page 20 of 36

21 0V 0V GPIOA_00 GPIOA_01 GPIOA_02 GPIOA_03 GPIOA_04 GPIOA_05 GPIOA_06 GPIOA_07 GPIOA_08 GPIOA_09 GPIOA_10 GPIOA_11 GPIOA_12 GPIOA_13 GPIOA_14 GPIOA_15 GPIOB_00 GPIOB_01 GPIOB_02 GPIOB_03 GPIOB_04 GPIOB_05 GPIOB_06 GPIOB_07 GPIOB_08 GPIOB_09 GPIOB_10 GPIOB_11 GPIOB_12 GPIOB_13 GPIOB_14 GPIOB_15 J2-A J2-B X2 MST_SO MST_SI MST_SCK MST_CS SLV_SO SLV_SI SLC_SCK SLV_CS 0V X3 J3 U2 U1 VCC IIC_SCL IIC_SDA 0V X4 J1-A J1-B X5 X1 0V ANA_03 ANA_01 ANA_00 ANA_02 Rev: 1.1 (Oct 2010) Page 21 of 36

22 5.3. SPI Interface Connector X3 contains the SPI interface. MST_CS[0] Output SPI master chip select output (channel 0). MST_SCK Output SPI master serial clock output. MST_SO Output SPI master serial data output. MST_SI Input SPI master serial data input. SLV_CS[0] Input SPI slave chip select input (channel 0). SLV_SCK Input SPI slave serial clock input. SLV_SO Output SPI slave serial data output. SLV_SI Input SPI slave serial data input. Power Supply 0V Power Ground The interface includes separate master and slave SPI interfaces. Pins of the GPIOA port can be sacrificed to either SPI master or SPI slave chip selects. These then form the remaining bits of the chip select buses mst_cs[16:0] or slv_cs[16:0]. In general three usages of the SPI interface become possible, as shown over: Rev: 1.1 (Oct 2010) Page 22 of 36

23 Master Mode mst_cs[16:0] mst_sck mst_so mst_si slv_cs slv_sck slv_si slv_so slv_cs slv_sck slv_si slv_so Slave Mode **slv_cs[16:0] slv_sck slv_si slv_so mst_cs mst_sck* mst_so mst_si mst_cs mst_sck* mst_so mst_si *) When connecting multiple slaves, care needs to be taken to make sure the clock outputs can be connected. For example they could be externally gated or made open drain. **) Always make sure that for channels configured to be SPI slaves always have their chip select inputs driven and not left floating. Hybrid Master-Slave Mode mst_cs[0] mst_sck slv_cs[0] slv_sck mst_so mst_si slv_cs slv_sck mst_cs mst_sck slv_si slv_so Rev: 1.1 (Oct 2010) Page 23 of 36

24 5.4. IIC Interface Connector X4 contains the I2C interface. IIC_SCL Input/Output IIC serial clock. IIC_SDA Input/Output IIC serial clock. Configuration jumpers J1-A and J1-B can be used to switch in/out on-board pull-up resistors for the I2C lines up to either 3.3 volts or 5 volts as per the following drawings. Rev: 1.1 (Oct 2010) Page 24 of 36

25 J2-A J2-B X2 IIC Interface 5V X3 J3 U2 U1 1K5 X4 X5 IIC_SDA IIC_SCL J1-A J1-B D2 X1 0V 0V Jumpers J2-A J2-B X2 IIC Interface X3 J3 U2 U1 IIC_SDA X4 X5 IIC_SCL 0V 0V J1-A J1-B D2 X1 No Jumpers J2-A J2-B X2 IIC Interface X3 J3 U2 U1 1K5 X4 X5 IIC_SDA IIC_SCL J1-A J1-B D2 X1 0V 0V Jumpers Rev: 1.1 (Oct 2010) Page 25 of 36

26 5.5. GPIO Port A Interface Connector X2 contains GPIO Port A interface. GPIOA_00 Input/Output Digital I/O, PWM, interrupt or pulsed. Can be filtered to form an analogue output. GPIOA_01 Input/Output Digital I/O, PWM, interrupt or pulsed. Can be filtered to form an analogue output. GPIOA_02 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_03 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_04 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_05 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_06 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_07 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_08 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_09 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_10 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_11 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_12 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_13 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_14 Input/Output Digital I/O, PWM, interrupt or pulsed. GPIOA_15 Input/Output Digital I/O, PWM, interrupt or pulsed. 0V Supply The GPIO pins can all be separately configured as digital input, digital output, PWM outputs, pulsed output or interrupt input. These pins can also be sacrificed as SPI chip selects as either a SPI master or SPI slave as described in section 5.3. Rev: 1.1 (Oct 2010) Page 26 of 36

27 For GPIOA bits 0 and 1 in PWM mode the output can be low pass filtered to form an analogue output using jumpers J2-A and J2-B. GPIOA_00 GPIOA_01 Jumpers J2-A J2-B X2 X3 J3 U2 U1 X4 X5 J1-A J1-B D2 X1 GPIOA_00 GPIOA_01 J2-A J2-B X2 Jumpers X3 J3 U2 U1 X4 X5 J1-A J1-B D2 X1 Rev: 1.1 (Oct 2010) Page 27 of 36

28 5.6. GPIO Port B Interface Connector X2 contains GPIO Port B interface. GPIOB_00 Input/Output Digital I/O. GPIOB _01 Input/Output Digital I/O. GPIOB _02 Input/Output Digital I/O. GPIOB _03 Input/Output Digital I/O. GPIOB _04 Input/Output Digital I/O. GPIOB _05 Input/Output Digital I/O. GPIOB _06 Input/Output Digital I/O. GPIOB _07 Input/Output Digital I/O. GPIOB _08 Input/Output Digital I/O. GPIOB _09 Input/Output Digital I/O. GPIOB _10 Input/Output Digital I/O. GPIOB _11 Input/Output Digital I/O. GPIOB _12 Input/Output Digital I/O. GPIOB _13 Input/Output Digital I/O. GPIOB _14 Input/Output Digital I/O. GPIOB _15 Input/Output Digital I/O. 0V Supply 5.7. Analogue Interface Connector X5 the analogue interface. ANA_00 Input Analogue input. ANA_01 Input Analogue input. ANA_02 Input Analogue input. ANA_03 Input Analogue input. Supply 0V Supply 5.8. LED Indicator The includes a green LED indicator to indicate that the circuit is powered correctly. Rev: 1.1 (Oct 2010) Page 28 of 36

29 6. Getting Started Use of the typically involves writing a C/C++ console application or a Visual C++ Windows GUI application which calls functions and tasks in the API provided by. A full definition of the API is provided in the API Specification, provided on the web-site. In order to rapidly build up applications and see how to link to the API, eight example applications have been built up. The example applications provided are described below. These are all fully documented in the Example Applications document, provided on the web-site. Configuration Example (for Windows) This example is very simple C/C++ console application for Windows showing how to call basic functions associated with SPI, I2C, GPIO and analogue IO. The example is a good starting point if you want to try the for the first time and want to see a simple console application. Rev: 1.1 (Oct 2010) Page 29 of 36

30 Windows GPIOTool (for Windows) This example application is a very simple Visual C++ GUI application showing how to interface to the general purpose IO (GPIO) pins. This includes both port A and port B GPIOs. Advanced Windows Analog/Digital IO Tool This is a more complex Visual C++ GUI application showing some of the more complex GPIO and analog input functions. Rev: 1.1 (Oct 2010) Page 30 of 36

31 Windows SPI Tool The Windows SPI tool is a windows GUI application in Visual C++ used to demonstrate both master and slave operation of the SPI interface for. Windows I2C Tool The Windows I2C tool is a windows GUI application in Visual C++ used to demonstrate both master and slave operation of the I2C interface for. Rev: 1.1 (Oct 2010) Page 31 of 36

32 Windows EEPROM Programmer This is a simple I2C and SPI EEPROM programmer written as a windows GUI application in Visual C++. It illustrates how to build a more complex application and also how to link to both I2C and SPI functions in the API. Rev: 1.1 (Oct 2010) Page 32 of 36

33 Configuration Example (for Linux and MacOS) This is a simple GCC program for Linux and MacOS to show basic setup of GPIO, I2C, SPI and Anlogue IO interfaces. Rev: 1.1 (Oct 2010) Page 33 of 36

34 I2C Checker Tool (for MacOS Xcode Cocoa) This is a simple GUI program for MacOS showing how to use to scan IIC devices from Xcode Cocoa. Scan Button Text Box Rev: 1.1 (Oct 2010) Page 34 of 36

35 7. Appendix A : Schematic See over. Rev: 1.1 (Oct 2010) Page 35 of 36

36 Rev: 1.1 (Oct 2010) Page 36 of 36 PC6/GPIFADR6 63 PC7/GPIFADR7 64 PD0/FD0 PD1/FD1 PD2/FD2 PD3/FD3 PD4/FD4 PD5/FD5 PD6/FD6 PD7/FD7 PE0/T0OUT PE1/T1OUT PE2/T2OUT PE3/RXD0OUT PE4/RXD1OUT PE5/INT6 PE6/T2EX PE7/GPIFADR8 RDY0/SLRD RDY1/SLWR RDY2 RDY3 RDY4 RDY5 CTL0/FLAGA CTL1/FLAGB CTL2/FLAGC CTL3 PB7/FD7 PC0/GPIFADR0 PC1/GPIFADR1 PC2/GPIFADR2 PC3/GPIFADR3 PC4/GPIFADR4 PC5/GPIFADR5 PB0/FD0 PB1/FD1 PB2/FD2 PB3/FD3 PB4/FD4 PB5/FD5 PB6/FD6 PA0/INT0# PA1/INT1# PA2/SLOE PA3/WU2 PA4/FIFOADR0 PA5/FIFOADR1 PA6/PKTEND PA7/FLAGD CTL4 CTL RXD0 RXD1 TXD0 TXD1 T0 T1 T2 RD# WR# INT4 INT5# BKPT IFCLK WAKEUP# SCL SDA DMINUS DPLUS AVCC1 AVCC2 RESET# VCC9 NC1 NC2 NC3 XTALIN XTALOUT VCC1 VCC2 VCC3 VCC4 VCC5 VCC6 VCC7 VCC A1 A RESERVED U1 CY7C68013A-AXC SCL 6 SDA 5 A0 1 A1 2 A2 3 WP 7 VCC 8 VSS 4 U3 24LC128 OUT 5 NC 4 IN 1 EN 3 U7 TPS73633 C32 12p XTL1 24MHz Vbus D- D+ Sld X1 C11 R6 1K5 R7 1K5 +5V C10 C33 12p C8 C9 C6 C7 C4 C5 C2 C3 2 R1 10K C31 4.7u C30 4.7u C1 C28 4.7u + + D1 1N4148 R2 10K R11 470R D2 LED Size A4 Title Sheet Rev Date Schematic July of 1 19 GPIO_A_00 GPIO_A_01 GPIO_A_02 GPIO_A_03 GPIO_A_04 GPIO_A_05 GPIO_A_06 GPIO_A_ X2 34-way header FPGA_00 FPGA_ FPGA_02 FPGA_ FPGA_04 FPGA_ FPGA_06 FPGA_ FPGA_24 FPGA_ FPGA_26 37 FPGA_28 28 FPGA_32 FPGA_ FPGA_34 FPGA_ FPGA_36 FPGA_ FPGA_38 FPGA_ FPGA_BUS[39:0] C D HOLD\ W\ VCC VSS S\ Q C23 U4 25P20 VCCAUX VCCO VCCO VCCO VCCO VCCO VCCO VCCAUX VCCAUX VCCINT VCCINT VCCINT VCCINT GPIO_A_09 GPIO_A_10 GPIO_A_11 GPIO_A_12 GPIO_A_13 GPIO_A_14 GPIO_A_ GPIO_A_08 GPIO_B_00 GPIO_B_01 GPIO_B_02 GPIO_B_03 GPIO_B_04 GPIO_B_05 GPIO_B_06 GPIO_B_ GPIO_B_09 GPIO_B_10 GPIO_B_11 GPIO_B_12 GPIO_B_13 GPIO_B_14 GPIO_B_ GPIO_B_08 GPIO_A_00 GPIO_A_ GPIO_A_02 GPIO_A_ GPIO_A_04 GPIO_A_ GPIO_A_06 73 GPIO_A_07 GPIO_A_ GPIO_A_09 GPIO_A_ GPIO_A_11 GPIO_A_ GPIO_A_13 61 GPIO_A_14 GPIO_A_ FPGA_BUS[39:0] CH1 CH2 CS\ 2 CLK 12 DI 13 U5 TLV0834 DO SARS D CH0 CH3 A ANA_01 ANA_02 ANA_ VCC ANA_00 1 ANA_CS\ ANA_CLK ANA_DI ANA_DO U2 XC3S200A-4VQ100 OUT 5 FB 4 IN 1 EN 3 U6 TPS V 2 C29 4.7u VREF VCC 14 C24 C25 M0 M M X5 6-way header 6 C17 C18 C15 C16 C13 C14 C12 1.2V C21 C22 C19 C20 R12 470R J2-A C27 C26 R13 470R J2-B VS0 VS VS2 29 PROG_B 100 R3 10K J5 DONE R10 300R RESET_N R4 10K CLK 40 TDO TMS 1 75 TCK TDI 2 76 CLKOUT 100 ANALOGUE GPIO PORT_A GPIO PORT_B R5 10K 5 R8 1K5 R9 1K J1-A J1-B 5V 5V X4 4-way header 4 VCC IIC_SCL IIC_SDA IIC_SCL IIC_SDA 5 6 I2C SPI SLV_CS SLV_SCK SLV_SI SLV_SO MST_CS 6 X3 10-way header SLV_CS SLV_SCK 97 4 SLV_SI SLV_SO 3 99 MST_CS MST_SCK MST_SI 93 MST_SCK MST_SI 7 8 MST_SO MST_SO