[[PageOutline]]

= Serial Peripheral Interface Bus (SPI) =
The Serial Peripheral Interface bus is a synchronous serial communication interface specification used for short distance communication primary in embedded systems. The interface was originally developed by Motorola and can be used in a master or slave configuration. It is typically used as a 3-wire bus containing the following signals (other than power and ground and chip-selects):
 * SCLK
 * MISO
 * MOSI
 * SS# (Optional Slave Select)

SPI can be a multi-slave bus if chip selects are used which are asserted by the host controller to enable one device at a time.

References:
 * http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus


== USB Expansion devices ==
A SPI master can also be added via USB expansion. For example:
 * [http://trac.gateworks.com/wiki/expansion/gw16113 GW16113 firmware-flexible USB 2.0 FS expansion]
 * [http://www.commell.com.tw/product/Peripheral/PCI%20Express%20mini%20card/MPX-24794S.HTM Commell MPX-24794S USB 2.0 FS SPI/I2C/GPIO expansion]


== Ventana ==

=== GW5220 ===
The i.MX6 Ventana GW5220 brings out the IMX6 ECSPI3 bus to the 6-pin J24 expansion connector for connection to a 3.3V TTL SPI slave device:
 * J24.1 - MOSI
 * J24.2 - MISO
 * J24.3 - SCLK
 * J24.4 - SS0#
 * J24.5 - 3.3V
 * J24.6 - GND

=== GW54xx (Revision E+) ===
The i.MX6 Ventana GW54xx brings out the IMX6 ECSPI2 bus to the 6-pin J32 expansion connector for connection to a 3.3V TTL SPI slave device:
 * J32.1 - MOSI
 * J32.2 - MISO
 * J32.3 - SCLK
 * J32.4 - SS0#
 * J32.5 - 3.3V
 * J32.6 - GND

=== Adding Kernel Support for Specific SPI Devices ===
In order to support the specific device you plan to connect an addition to the GW5220 device tree must be made.

1. Follow [http://trac.gateworks.com/wiki/linux/kernel#BuildingtheLinuxkernelout-of-tree these instructions] up to and including step 5 of "Building the Linux Kernel"
2. Open the file at {{{.../linux-imx6/arch/arm/boot/dts/imx6qdl-gw52xx.dtsi}}} and find the node labeled "&ecspi3" (if absent, jump to the above section before continuing)
3. In the same location as the comment in step 5 of the above section, add your appropriate device configuration in a node beginning with "flash: "
4. Continue the instructions from step 1 to finish building your new kernel

An example of a properly made configuration node for a m25p32-vme6g nor flash device would be:
{{{#!c
flash: m25p80@0 {                         /* "m25p80@0" parameter is the driver responsible for controlling your device */
        compatible = "m25p32";            /* "m25p32" parameter is your device ID string */
        spi-max-frequency = <30000000>;   /* assigned value is your device frequency specified by its datasheet (in decimal) */
        reg = <0>;                        /* is generally 0 for single device connections */
        #device-width = <1>;              /* These next three lines are not comments, but rather specially formatted
        #address-cells = <1>;              * attributes that the driver will receive. The actual values assigned here
        #size-cells = <1>;                 * are device specific, and should be entered after consulting the data sheet
                                           */
        partition@0 {                     /* The label of the 0th partition; following partitions follow the "partition@X" format */
                label = "data";           /* The name of this partition  */
                reg = <0x0 0x2000000>;    /* The starting address, followed by the length of the partition (in hex) */
        };
};
}}}
Note that the values shown in the above node are specific to the m25p32-vme6g, and can vary greatly from the actual device you are using. Replace attribute values as necessary.

When searching for your device ID string or its controlling driver, searching via a LXR site like the one at [https://lxr.missinglinkelectronics.com/linux missing link electronics] for your device name can be helpful.


== Laguna ==
While SPI is used for on-board FLASH storage for many Laguna boards, it also is brought out to the J9 expansion connector available on the Laguna GW2388:
 * J9.2 - CS#
 * J9.4 - SCLK
 * J9.6 - MISO
 * J9.8 - MOSI
 * J9.10 - GND

[[Image(spi2388.png,800px)]]