ublox: rework device initialization sequence

uBlox devices present their USB interfaces well before those interfaces
are ready to respond to any commands.  The documentation says to monitor
the 'greeting text' to detect readiness, but this 'greeting text' is not
actually specified for any device other than the TOBY L4.

What seems to work is to probe the device with 'AT' commands until the
device responds, and then to wait an additional second before
proceeding.  The TOBY L4 reliably sends its 'greeting text' (+AT: READY)
within this interval.

It would be more rigorous to actually wait for the 'READY' indication
for the TOBY L4, but that would require knowing the device model before
the device model is actually queried.  This is doable via the USB
product ID, but overkill when the above heuristic seems to work
reliably.

Before this patch, the ublox plugin was trying to achieve something like
the above with the g_at_chat_set_wakeup_command() function, but that had
some issues:

i)  it did not work reliably, in particular failing badly on the TOBY L4
with responses getting out of sync with commands
ii) it was an inappropriate use of the wakeup_command which is intended
for devices that may sleep when there is no communication during some
interval

This patch adds an init sequence that probes the device for readiness
before continuing with initialization.

0 files changed, 0 insertions, 0 deletions