+
−The highest baud rate supported by "standard" PC serial ports is 115200 bps,
+
−but Calypso UARTs can go quite a bit faster.  Being clocked with 13 MHz (a
+
−standard frequency in the GSM world), these UARTs can produce non-standard
+
−(outside of the GSM world) baud rates of 203125, 406250 and 812500 bps.  When
+
−working with Motorola C1xx and Openmoko GTA01/02 phones which present a debug
+
−and programming serial interface on a 2.5 mm headset jack, one can make use of
+
−these high serial baud rates by using a USB to headset jack programming cable
+
−based on one of the better USB-serial chips that can support these GSM special
+
−baud rates well above 115200.  The two USB-serial chips that are known to work
+
−in this manner are CP2102 and FTDI, although each of the two requires its own
+
−special quirks described below.  Other USB to serial cables use chips which
+
−don't support the high baud rates in question, and therefore are limited to
+
−115200 baud max like a "standard" PC serial port.
+
−
+
−FreeCalypso tools can use these high serial baud rates in the following ways:
+
−
+
−* When you use fc-loadtool to dump and program GSM device flash memory
+
−  (flashing firmware images), the transfers get annoyingly slow at 115200 baud
+
−  if you have to do it a lot.  Switching to 406250 or even better 812500 baud
+
−  makes them go considerably faster.
+
−
+
−* Some of our target devices have large enough RAM to execute a GSM firmware
+
−  image entirely from RAM without flashing - very handy for development and
+
−  experimentation.  The tool used to run these RAM-based images is fc-xram,
+
−  and it also supports the option of using high serial baud rates for the image
+
−  transfer for the same reason: repeatedly transferring 1.5 MiB images over
+
−  115200 baud gets tiresome.
+
−
+
−* If you are building your own GSM firmware (either FC GSM fw or one of our
+
−  TCS211-based hacks), you can make it run its RVTMUX interface at 406250 or
+
−  812500 baud.  We used this trick when we tried to make TCS211 with D-Sample-
+
−  targeting UI (176x220 pix LCD, 16 bits per pixel) send its virtual LCD raster
+
−  blits out the serial port.  Our rvtdump and rvinterf utilities support this
+
−  mode of operation by providing options to select different baud rates.
+
−
+
−Using CP2102 adapters
+
−=====================
+
−
+
−CP2102 chips have a built-in EEPROM that contains (among other things) a
+
−32-entry table in which the supported serial baud rates are programmed.  In
+
−order to support the special GSM baud rates, these rates need to be added to
+
−that table, displacing some other entries.  The convention established by the
+
−Pirelli DP-L10 phone (has a CP2102 built in and programmed at the factory for
+
−GSM baud rates) is that 203120 baud takes the place of 230400, 406250 takes the
+
−place of 460800, and 812500 takes the place of 921600.
+
−
+
−Because you need a special cable anyway to make the necessary physical
+
−connection to the debug/programming serial port presented on a 2.5 mm headset
+
−jack, you will probably be buying the requisite cable from a specialized
+
−professional vendor.  In that case it is that vendor's responsibility to sell
+
−you the cable with the CP2102 chip already programmed with GSM baud rates:
+
−because the physical construction of the cable (2.5 mm headset jack on the
+
−serial end) makes it specific to GSM devices, and all known GSM devices use a
+
−13 MHz clock or some integer multiple thereof, it is pointless for a
+
−physically-GSM-specific cable to be set up for 230400/460800/921600 baud when
+
−all known GSM devices will need 203125/406250/812500 baud instead.
+
−
+
−If you making a CP2102-based serial cable yourself (either for your own personal
+
−use or professionally/commercially), please follow these instructions for baud
+
−rate programming:
+
−
+
−http://bb.osmocom.org/trac/wiki/Hardware/CP210xTutorial
+
−
+
−If you follow the procedure given on that page, your CP2102 will be programmed
+
−the same way as the one in the Pirelli DP-L10 (Foxconn's original factory
+
−programming).
+
−
+
−The serial port handling code in FreeCalypso host tools is written to request
+
−B230400 from termios when 203125 baud is desired, likewise B460800 for 406250
+
−baud and B921600 for 812500 baud.  Therefore, if you have a CP2102-based cable
+
−with properly programmed EEPROM, everything will Just Work.
+
−
+
−Using FTDI adapters
+
−===================
+
−
+
−Unlike CP2102, FTDI adapters don't require any non-volatile EEPROM programming
+
−for GSM baud rates, but they have a different pain point - arguably a worse one
+
−- that is entirely a software issue.  The API which the Linux kernel provides
+
−to userspace applications for opening and configuring serial ports provides no
+
−clean, sensible way for an application to request a particular baud rate that
+
−is not in the predefined-once-and-for-all list, and to make it unambiguous to
+
−the in-kernel driver exactly what it wants.
+
−
+
−The method provided by the ftdi_sio driver in the standard Linux kernel is
+
−gross, and I (Space Falcon) refuse to use it.  The serial port handling code in
+
−FreeCalypso host tools is written for the clean CP2102 way, and is *not* muddied
+
−with the muck that would be necessary to get the high GSM baud rates with an
+
−unpatched ftdi_sio driver.  Therefore, if you would like to use one of the high
+
−GSM baud rates with FreeCalypso with an FTDI adapter, you will need to dirty
+
−your Linux host system with a hacky kernel patch.  The patch provided in
+
−linux-2.6.37.6-ftdi_sio.c.patch (made against Linux 2.6.37.6, which is what I
+
−use - came with Slackware 13.37 - adapt as necessary for your kernel version)
+
−makes the ftdi_sio driver behave like a GSM-programmed CP2102: termios B230400
+
−turns into 203125 baud, B460800 turns into 406250 and B921600 turns into 812500.
+
−
+
−This patch won't break other software (*cough* osmocom-bb *cough*) that does
+
−use the "standard" ftdi_sio way of requesting high GSM baud rates, i.e., both
+
−ways of selecting these baud rates should still work, but if you have other
+
−(non-GSM) serial devices on the same system which need 230400, 460800 or 921600
+
−baud, those will break.
+
−
+
−Using adapters built into phones
+
−================================
+
−
+
−The Calypso chip has no native USB capabilities, thus if a Calypso phone
+
−presents a USB charging+data port to the user, it must have a USB to serial
+
−converter built in.  The only phone we currently know of that does this is
+
−Pirelli DP-L10, and its built-in USB-serial adapter chip is CP2102.  It has
+
−already been programmed with the correct GSM baud rates on Foxconn's original
+
−production line, thus one can always use 812500 baud with FreeCalypso tools on
+
−this phone and it will Just Work.