Hardware/CubeSat Gumstix

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This board is the result of a diploma work. It is meant to be a first evaluation version of a Cubesat image processing board.

Type FPGA Rack Schematic UCF Description
2015 FPGA + Gumstix 2015 FPGA + Gumstix 2015 schematic

top view
FPGA + Gumstix 2015 UCF FPGAs: Spartan 6 XC6SLX45, XC6SLX100 or XC6SLX150

SPI flash: M25P64-ME (64 Mb, 1 bit data width)

A short presentation is given on the Institute's website.



The 24-pin camera interface connector is foreseen to be used with different camera models.

It has:

  • a 3.3 V power supply
  • 2 serial control lines
  • 4 framing lines
  • 12 data lines
  • 4 camera control lines

It has been tested with a OV7670 camera module.


The board hosts a ADS8028 12-bit, 1 MSPS, 8-channel analog-to-digital converter.

The ADC is powered with the input 5 V for the analog part and with a local 3.3 V for the digital lines. The voltage reference input connects to the analog power supply via jumper J5.

Inputs AIN0 to AIN4 are used to monitor the board's power supplies. Inputs AIN5 to AIN7 are sourced by connector J9.

The connection to the FPGA is given in the following table:

CS_n C16 chip select, active low
SCLK B12 serial clock
DOUT A18 slave out (MISO)
DIN C17 slave in (MOSI)
PD_n_RST_n B18 power down or restart, active low
TM_BUSY A17 busy aquiring temperature


A Gumstix board can be plugged onto the CubeSat board. It is provided for the image processing tasks. When using a Gumstix, the FPGA bank 2 must be powered with 1.8 V.

The Gumstix connector could be used for other purposes such as adding external RAM to the FPGA.


The processor's serial console, UART 3, is connected to a mini-USB connector on the side of the board via an FTDI USB-UART interface.


The Gumstix UART 1 connects to the FPGA. Two test points allow to monitor these signals and check the logic levels of the Gumstix to FPGA lines. Achieved data rates range up to xxx kbit/sec.

The connection is given in the following table:

TxD1 V21 Gumstix TxD out
RxD1 C22 Gumstix RxD in


The Gumstix acts as a master of an SPI link to the FPGA. Achieved data rates range up to 48 Mbit/sec.

The connection is given in the following table:

CS_0 W22 chip select, active ?
SCLK H21 serial clock
MOSI B22 Gumstix out, FPGA in
MISO A21 Gumstix in, FPGA out

Extended memory bus

The Gumstix extended memory bus, with 10 address and 15 data bits, is also connected to the FPGA. This should allow very high data rates, but hasn't been tested yet.


The reset pin is connected both to a press button and a pull-up resistor.

OBC connectors

Two 22-pin Else spring-loaded connectors are used to connect to the On-Board Computer (OBC). Connector B allows to use differential signalling, as it is the case for SpaceWire.

Peripheral connectors

Two 24-pin peripheral connectors are provided. Both comprise 2 power supply pins and 22 FPGA I/O.

Power supplies

The board receives a 5 V power input. 4 DC/DC converters provide power for different components.

FPGA supply

On the FPGA:

  • VCC33 is used by the FPGA for VCCAUX, the SPI flash, the JTAG connector, bank 0 and bank 3
  • VCC18/33 is used for FPGA bank 1
  • VCC25/33 is used for FPGA bank 2
  • VCC12 is used for the FPGA core

Bank 0 connects to the camera and the ADC

Bank 1 is connected to the Gumstix and 1.8 V should be used. The Gumstix board could be replaced by a memory board which might require 3.3 V signalling

Bank 2 connects to the On-Board Computer (OBC). The OBC connector B allows to have SpaceWire differential lines. If so, one has to mount the 165 Ω serial and 140 Ω parallel resistors. Normal CMOS signalling requires 0 Ω serial and no parallel resistors.

Bank 3 connects to the spare connectors on the side of the board.

Test designs

Different test designs have been elaborated:

To do

Any board that doesn't need a modification is obsolete.

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