26 Jul
2013
26 Jul
'13
10:55 p.m.
Hi folks,
Seems not all phones use 3V signaling if the PHONE-side VCC pin is tied
to 3V.
This one insists on 1.8V : BLU SAMBA JR PLUS
Is this trick of tying VCC to 3V standard behavior?
For future version of the board, it might be interesting to tie the VCC
pin to an ADC input, to detect different voltage levels so the firmware
can wait until phone decides to use 3V.
Cheers
Tom
26 Jul
26 Jul
11:05 p.m.
Excerpts from Tom Schouten's message of 2013-07-26 22:55:32 +0200:
Hi folks,
Seems not all phones use 3V signaling if the PHONE-side VCC pin is tied
to 3V.
This one insists on 1.8V : BLU SAMBA JR PLUS
how does the phone behave?
Is this trick of tying VCC to 3V standard behavior?
no, it is not standard. It just works (most of the time).
And it should not damage the SIM nor the phone.
For future version of the board, it might be interesting to tie the VCC
pin to an ADC input, to detect different voltage levels so the firmware
can wait until phone decides to use 3V.
this will be done in the next board
Cheers
Tom
11:19 p.m.
On 07/26/2013 05:05 PM, Kevin Redon wrote:
good
( next to some GPIOs maybe ;)
Excerpts from Tom Schouten's message of 2013-07-26
22:55:32 +0200:
if the at91 doesn't respond, the phone goes through the following
power/reset sequence, about 1 second apart:
1.8V
3V
3V
1.8V
the at91 seems to mostly interpret the 1.8V serial line correctly, so
the phone just starts talking at 1.8V until this eventually goes wrong.
Hi folks,
Seems not all phones use 3V signaling if the PHONE-side VCC pin is tied
to 3V.
This one insists on 1.8V : BLU SAMBA JR PLUS
how does the phone behave? Is this trick of tying VCC to 3V standard
behavior?
no, it is not standard. It just works (most of the time).
And it should not damage the SIM nor the phone.
For future version of the board, it might be
interesting to tie the VCC
pin to an ADC input, to detect different voltage levels so the firmware
can wait until phone decides to use 3V.
this will be done in the next board
30 Jul
30 Jul
8:15 p.m.
for the MITM, there seem to be a couple of variables to play with (as
compared to passive sniffing) that make it a little more reliable:
- wait for X number of power cycles, i.e. don't send ATR until the 3V3
one comes up
- manipulate ATR: it seems possible to set the voltage class explicitly
The power-wait works for the BLU phone I mentioned, and the Nexus One.
N1 also starts out with a different voltage (about 2.3V, weird..)
27 Jul
27 Jul
3:23 a.m.
Hi Tom,
On Fri, Jul 26, 2013 at 04:55:32PM -0400, Tom Schouten wrote:
For future version of the board, it might be
interesting to tie the
VCC pin to an ADC input, to detect different voltage levels so the
firmware can wait until phone decides to use 3V.
this is more or less what we intended to do from the beginning, but
somehow there was an error in the schematic so we had to resort on this.
If I remember correctly off my head the story goes like this:
So the original idea was to always forward the same VCC voltage from the
phone to the sim card by means of a switch, and alternatively provide
the SIM-side VCC with voltage from a regulator.
However, as both the regolator output and the forward-switch output were
connected together, and the regulator could not deal with voltage beping
present at its output while being disabled, the circuit never worked as
expected.
We didn't touch the simtrace v1.x hardware for a long time, as Kevin
started work on a completely different v2.x hardware years ago.
However, due to lack of time and other projects, this never really
emerged beyond the early design phase (as far as I know).
If I was to do an updated version of simtrace, I would also move to an
at91sam3s instead of the at91sam7s, as the former has more USB endpoints
enabling the CCID + CDC-ACM simultaneous operation for the MITM mode.
Regards,
Harald
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
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4 comments
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participants (3)
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Harald Welte -
Kevin Redon -
Tom Schouten