During FOSDEM 2010 I had discussion with Ulf Samuelsson from Atmel and few other guys about developer boards. What is required on them and what should be avoided. Some time later I had a talk with one person about new OMAP3 based board and what I would like to see on it. So I decided to write something in public.
So far I used mostly ARM developer boards from ST Microelectronics/ST Ericsson, Atmel, Cirrus Logic, Intel, Simple machines, Bug Labs, Texas Instruments. Some were better then others etc. But what ideal developer board should have? Let me try to create a list:
- 2 serial ports (one can be null modem, second should have RTS/CTS/DTR lines)
- working Ethernet not placed on USB bus (so it works when USB does not)
- powered USB host port (more then one would be great)
- USB device port
- JTAG connector
- one power input — +5V or +12V — other should be forbidden as those ones can be taken from PC PSU which can power multiple devices at same time
- SD/MMC slot — even if it is over slow SPI (like on Sim.One — 250KB/s max)
- GPIO pins
- I²C bus
- SPI bus
- keypad with Up/Down/Left/Right + Enter at least
- easily reachable reset button (pins to short are acceptable as micro switch can be put on them)
- few LEDs controlled by system
- all connectors put on one or two edges of board — top one + one of side ones are ok (Atmel at91sam9m10-ekes for example)
- mounting holes (so board can be mounted on A5 sheet holder for presentation at stand)
- backup battery for RTC
- U-Boot
- quite fresh kernel (not NHK-15 due to 2.6.20 kernel which is 3 years old now)
What to avoid:
- female serial port connectors (Atmel NGW100) — most devs will find 3 null modem cables before straight one
- flat cables which connect “debug boards” with main board (Openmoko phones, NHK-15 from ST Ericsson)
- RJ45 connectors for serial console (Sim.One) — DB9 or properly done USB->RS232 adapter on-board are best
- placing connectors on all edges (BeagleBoard — but it had to be cheap)
- non standard bootloaders (U-Boot is what I prefer)
- Ethernet on USB (Bug 2.0) — it is hard to use when you have problems with USB Host
- jumpers (Atmel boards)
- non standard connectors (Bug r1.2 and it’s Handylink crap — next versions use iPod connector which is easier to use)
I am trying to not cover should developer board contain display with touchscreen or not as it depends on type of board. But if screen is present then more then QVGA (320×240) would be nice (WVGA anyone?). Some kind of video out connector can also be used but would be nice to have one of VGA/DVI/HDMI so normal PC monitor can be used — Composite video and S-Video require searching for some kind of TV…
Which boards are my favorites? There are few:
- FriendlyARM with WVGA screen — cheap product which gives access to everything needed to start with embedded Linux
- Atmel AT91SAM9263-EK — my first own developer board
- BeagleBoard Cx — has own problems but I like the power of it
Which FriendlyARM board/display do you recommend: http://www.watterott.com/en/FriendlyARM?
I would take Micro2440 – WVGA screen is more usable then QVGA one. Other option is Mini2440 + VGA board but I do not know details of it.
I disagree with the preferred rs232 gender. A male db9 being used as console always requires a seperate gender changer, especially with usb-serial cables. Ports that are typically used for console are lkkely to be conneted to a host and thus should have client connectors.
This depends on board and use of it I think.
For those which are used as clients for host female DB9 is more useful as you can plug usb-serial cable directly. This is done that way on BeagleBoard XM.
But not each board is used that way. Many are used as autonomic systems.