User guide

SFSU - Embedded Systems Tutorial Nano- Electronics & Computing Research Lab

The hardware can be broken down in the following subsystems.

1. Memory Subsystem

2. Video Pipeline Subsystem

3. Touch Panel Subsystem

Memory Subsystem

The FPGA provides multiple options for memory storage. It provides on chip memory, off chip SRAM

FLASH and SDRAM and a SD Card SPI interface. In this chapter, SDRAM is used as a source for the

Scatter Gather DMA for VGA controller. SRAM is not used for this particular design. On-chip memory

of the Cyclone 4 FPGA is used to store local data for the application program run on Nios II processor.

The stack for the application is built in the on chip memory itself for faster access. Flash memory is

included in the system for program code storage. Flash programmer in Nios II IDE is used to program the

code into the flash. When this is done, the FPGA will boot up with the Nios II processor for image

display and the application will load automatically.

The SD Card controller needs to be included to provide appropriate control and data signals

for SPI interface, which connects the SD Card socket to the processor. Image from the SD Card will be

read out using simple memory pointers. The SDRAM is used as a frame buffer to store images for the

VGA controller to read. The SD Card cannot feed images to the VGA controller and hence SDRAM is

required as a buffer to connect to the VGA controller.

Software Design

For software implementation the VGA module, touch screen and SD Card are initialized first. Then a

home screen appears on the T-Pad which allows the user to touch and initialize the SD Card to read the

images. After the image is displayed by the pixel buffer on the T-Pad, the character buffer displays the

ALU options. After the user selects/touch one of the options of ALU, the character buffer is refreshed

and the result is displayed. After the result is displayed, the software waits for the touch input to any other

option and respective results are shown.

For initializing the touch screen and the VGA, Hardware Abstraction Layer is used provided by Altera.

The SD card controller is initialized using SPI. Once these components are initialized, the home screen

appears on the T-Pad’s screen. After the user selects a particular mode, images are read one by one from

the SD Card. Then using JPEG library, we decode the image data into hex format. This hex data is passed

to the buffer and pushed into video pipeline. Image corresponding to this data is then displayed. The

latency with which the image is displayed depends on the size of the hex data and therefore ultimately on

the image size. The flow chart for the software is shown below: