[Gta04-owner] What is GPIO175 "HOST_WAKE_WWAN" for?

[Dr. H. Nikolaus Schaller]

Hi Neil,

Am 14.12.2011 um 22:02 schrieb NeilBrown:

> 
> Hi,
> Looking at the schematic there are two GPIO pins connected to the GSM module.
> 
> 176 "3G_WOE" is apparently for the GSM module to use to wake the CPU when
> something is happening,

Yes. It will be moved to the GPIO10 on the A4 board since this will allow to
power down the GPIO block #6 during sleep.

The function appears to work and I have committed a simple patch for the
board file so that a wakeup interrupt is being displayed if you ring up the
device or it receives a SMS or is being reset by AT_ORESET.

> but what is 176 "HOST_WAKE_WWAN" for?  Is it out from the CPU and IN to the
> GSM, or the other way?
> Any hints?

It is to be used if the module has no USB interface but SPI. The USB interface
can wake up the module automatically (by USB handshaking). Since we don't
use SPI this pin has no function. On the GTA04A4 board the SPI interface will
be removed and GPIO176 will be reassigned (optional keyboard IRQ).

> And still curious - what is the change made to the later board to make it
> possible to power-down the GSM module?

Christoph already wrote: it can control the on/off function which is a power toggle
mode. In the meantime AT+CFUN=0 and suspending USB should have the same
effect. Controlling this through the CPU allows to keep the module completely
disabled while the CPU boots and reduces the power-up energy budget. Until
the CPU has enabled USB.

Nikolaus