Lattice or Xilinx

Ignacio García Pérez iggarpe at
Thu Sep 10 07:53:18 EDT 2009

2009/9/10 Wolfgang Spraul <wolfgang at>

> Ignacio,
> > I would say that for a portable device the MOST important feature, by
> far,
> > is the power consumption, and even the latest low power devices have
> > comparatively (to ASICs) high power requirements.
> What are the lowest power consumption FPGAs you know about? How much power
> do they consume?

The lowest power I know are actualy CPLDs (coolrunner by Xilinx). That means
they have non-volatile configuration and have less logic resources as
compared to FPGAs.

> I think one idea was to just leave an unpopulated place for an FPGA on the
> board, so we could still sell the device to regular users, but it would
> have an easily accessible FPGA option for hacking projects.

Do you really have so much spare real state on the PCB ?.

Note also that you need room not only for the FPGA itself but also for:

1- Connector (huge if you want to make all those I/O pins useful).
2- A CPLD to connect the FPGA programming interface to the SoC.
3- Power regulators (for example, Spartan 6 use 1.2V core voltage), and
possibly power management circuitry too to save power when no in use.

And no matter what FPGA/connector you choose you won't fullfill the needs of
all the potential users, which I believe will be anyway a minority in the
whole user base.

> Or we offer two versions, one with and one without FPGA?

In order to make that practical you'd need to share same form factors,
enclosure, etc, and thus you'd be making the device possible larger than

Seriously, I don't think the potential user base for tinkering justifies the
inclusion of an FPGA in the design. If you want to provide extensive I/O
capability, just add a host USB port. Supply of external power IS A MUST,
but 100mA would be more than enough (and should be switchable from the SoC).
And it must be a separate USB port, different from the device port used to
connect to the PC. I you want to go a bit more far, add an special connector
with I2C, SPI and power.

That is more than enough for the average hacker. If your project is so
complex or needs so much bandwidth that hostUSB+I2C+SPI is not enough,
neither the FPGA would have been (assuming and low-end, cheap and
non-power-hungry FPGA).


P.S: got the Ingenic docs. Just haven't had time to properly review them.
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