[gta02-core] Calypso's last dance

Werner Almesberger werner at openmoko.org
Thu Jul 23 05:08:37 CEST 2009

The gta02-core design still lacks one major component: the modem.

So far, the plan was to use the Calypso. However, there are a few

- we can't just use Openmoko Inc.'s design because Openmoko Inc.
  hasn't released it (yet). Openmoko Inc. can't just release the
  Calypso design because there is an NDA forbidding this between
  Openmoko Inc. and TI. We don't have any contacts in TI we could
  use to try to renegotiate that NDA or to do something to a
  similar effect.

- the Calypso is a complex RF circuit, so even copying an existing
  design would be hard work, with a high risk of introducing

Furthermore, there is no immediate plan to produce more devices
that use the Calypso. So if gta02-core uses the Calypso, it may
well be the last time we see this chipset. This of course raises
the question how much work we want to put into this, and if we
couldn't do something more interesting instead.

Until recently, we knew no suitable alternative. However, a few
weeks ago, we discovered a very compact 3G module that would fit
inside a slightly modified GTA02 case: the GTM501 made by a company
called Option.


As far as I can tell, using the GTM501 instead of the Calypso would
be relatively easy if we accept that the existing GSM antenna will
be a poor fit. Specifically, the necessary changes should be:

- addition of a 3.6 V/3 A DC-DC converter

- switch Bluetooth to UART and the modem to USB

It should be possible to prototype most of the 3G subsystem with
existing GTA02 hardware, reducing the design risk.

Using the GTM501 in gta02-core would not only yield a much sexier
device, but it could also serve as a partial prototype for a real
future device.

Now, all this depends on whether we can obtain a number of samples
from Option and whether we can get them to agree on conditions for
access to technical documentation that are compatible with our

So I wouldn't give up on the Calypso just yet, but I will approach
Option and see what I can achieve. To clarify our position, I've
prepared the "Disclosure Requisites" whitepaper described in my
previous posting.

At the same time, if anyone has sufficiently high-ranking contacts
in TI who might help with getting permission for Openmoko Inc. to
release the Calypso schematics and maybe the layout as well, please
speak up.

- Werner

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