Add a theoretical Wi-Fi and display component

This section of the guide describes how to add a Wi-Fi or screen component to your system. In both cases, non-specific third-party IP is considered. Although the specifications of the IP are hypothetical, you can find comparable third-party products on the market. This information is designed to help you integrate any third-party IP into a secure IoT device system.

The previous sections of the guide dealt with combining the components in the SoC. Both the Wi-Fi and screen component are part of the system but not part of the SoC.

Wi-Fi component specifications

For a Wi-Fi component, we assume that you are using an off-chip Wi-Fi component. The component has a dedicated processor and its own memory, which contains the whole TCP/IP stack. These features mean that you do not require as much memory on your SoC. This guide assumes that the Wi-Fi component supports at least some of the following communication interfaces:

  • UART
  • SPI
  • I2C

How to connect these interfaces to the SoC is explained in Attach external components to an SoC.

The data throughput varies depending on the communication interface that is used. It is reasonable to expect 4Mbit/s data throughput over UART and 10Mbit/s data throughput over SPI.

Note: If the SoC will be produced at high volume levels, consider including the Wi-Fi module as part of the SoC. An on-chip Wi-Fi component can connect to a bus matrix through a compatible bus matrix interface.

Display component specifications

For a screen component, we assume that you are using an LCD touchscreen about 3 inches in size, with 320x480 pixels. The display connects to the SoC using either an I2C or SPI interface. We also assume that the display has its own built-in controllers and display buffers.

Attach external components to an SoC

The previous sections of the guide identify communication interfaces that the third-party Wi-Fi or display component are likely to support. Other third-party components are also likely to support these interfaces. To connect these kinds of third-party components to your SoC, you must provide the appropriate outward facing communication interfaces on your SoC. The following table describes how you can provide these interfaces:

Communication interface Methodology
UART Include an APB-compatible peripheral that provides an external UART interface. The CMSDK includes a basic UART. Alternatively, you could use the more advanced PL011 UART.
SPI Include an APB-compatible peripheral that provides an external SPI interface. Arm supplies the PL022 SSP for this purpose.
I2C Include an APB-compatible peripheral that provides an external I2C interface. Arm does not currently offer any I2C connector IP. We recommend you investigate IP offered by third parties.

In the example SoC for this guide, connect APB-compatible peripherals to the APB4 PPC.

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