Changes

This Technical Note describes the implementation of the [https://developer.android.com/things/sdk/pio/spi.html APIs related to the SPI bus] to access the SPI bus TBD SPI4 of the SBCX platformin the form of a native library. The solution was tested with Android 4.4.3.

As stated in the introduction, the solution has been tested on a platform running Android 4.4.3. From the software standpoint, this platform is a good example of an implementation where significant changes have been done to the Android Open Source Project (AOSP) in order to use Android it on an industrial embedded device. Some of these changes modify the Android security model. In many cases, this is acceptable because the overall security of the product is not compromised (for instance, many devices used for industrial applications are not connected to the Internet and the physical access is granted to authorized personnel only). In general, system integrators have to assess these

The Some of these changes modify the Android security model. In many cases, this is acceptable because the overall security of the product is not compromised (for instance, many devices used for industrial applications are not connected to the Internet and/or the physical access is granted to authorized personnel only). In general, system integrators have to assess the impact of such changes to verify that the resulting configuration meets the system requirements. With regard to the platform here considered, the following is a not exhaustive list of the changes with respect to the standard/typical Android configuration used on mobile devices:*As the non-volatile storage device is a NAND flash, [http://www.linux-mtd.infradead.org/doc/ubifs.html UBIFS ] file system has been used

*U-Boot has been used as bootloader*Some of the device files are directly accessible from the application layer.

Development have been performed on the following platform:<pre>* CPU: based on NXP/Freescale iAndroid Studio 3.MX6 Dual core* SOM: Axel lite1* carrier board: [[:Category:SBCBuild #AI-AXEL|SBC-AXEL]]* Android Version: 4173.4.3 (Jelly Bean)4670197, built on March 22, 2018* LCD adapterJRE: TI-DF 1.08.00_152-CS102015 release-1024-b02 amd64* Nor Spi memoryJVM: M25P40 [https://wwwOpenJDK 64-Bit Server VM by JetBrains s.googler.itoAndroid SDK API 27</url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwihmJW5sq3aAhUHGewKHSCnCzIQFggtMAA&url=https%3A%2F%2Fwww.micron.com%2F~%2Fmedia%2Fdocuments%2Fproducts%2Fdata-sheet%2Fnor-flash%2Fserial-nor%2Fm25p%2Fm25p40.pdf&usg=AOvVaw0bupn15ZbP92k4y-oQhYQE datasheet]pre>

!Onepiece Signal name!Pin#

==ImplementationSoftware implementation== The following picture shows the organization of the software layers. [[File:SBCX-Android-4.4.3-SPI.png|thumb|center|600px|Software stack]] The solution depicted on the left is fully compliant with the Android/Android Things recommendations. The access to the I/O interface—the SPI bus in this case—is managed by the Peripheral Manager and by a specific service.

=== Managing the device connection Requirements ===In order to open a connection to a particular SPI slaveTo implement such solution, you need to know the unique name of following requirements must be met:*The Linux kernel must support [https://www.kernel.org/doc/Documentation/spi/spidev spidev]*The device file must have the permissions as shown in [[#Managing the busdevice connection|this section]].Boot *The device tree must be modified in order to instantiate the developer board and run SPI bus to be accessed: it is enough to enable the following commands from the serial console<code>escpi4</code> peripheral into SBCX device tree

Is === Example project===An [[#Downloads|example project]] is provided to illustrate how to use the native library. It includes the library itself and a simple application which reads the device identification data of the flash memory (<code>READ IDENTIFICATION</code> command).[[File:Spi test.png|thumb|center|600px|Test application]]==== Managing the device connection ====In order to open a connection to a particular SPI slave, you need to know the unique name of the bus. The get this name, run the following command from the serial console:<pre>root@sbcx:/ # ls /dev/spi* -alcrw-rw-rw- system root 153, 0 1970-01-01 00:00 spidev32765.0</pre>It is important to note that the above method is the only method one available in order to retrieve the spi SPI device name and because <code> getSpiBusList()</code> function is not implemented within the library.

Once you know the target this nameis known, the api of APIs defined by Android Things can be used to access the library bus because the library—named <code> eu.dave.spi_dev</code> follow the Android things nomenclature —is consistent with them:

 ==== Configuring clock and data modes ====

==== Transferring data ====

*<code> void WriteByte(byte symbol)</code> For : to transfer a byte without reading the response from the device.*<code> void WriteBuffer(byte[] data, int len)</code> For : to transfer a buffer to the device without processing the response.*<code> void Transfer(byte[] tx_data, byte[] rx_data, int len)</code> For : to transfer a buffer smaller than the length of the receiving one.*<code> void Transfer(byte[] tx_data, byte[] rx_data) </code> For : to transfer and read a buffer with the same length.*<code> void Transfer(byte symbol, byte[] rx_data, int len)</code> For : to transfer a byte and read a buffer of length ''len''.