CP210x High Baudrates Tutorial¶
This page will describe the procedure of programming high, non-standard baudrate mappings to a SiLabs CP210x serial converter using Linux, needed by the burst_ind branch.
Small adapter PCBs to which you have to solder your own cable + plug can be bought quite cheaply on eBay and AliExpress. Ready-made adapter cables with the CP2102 can be bought from shop.sysmocom.de
So far this tutorial has only been tested with the CP2102, but this seems to be the most common chip anyway.
How it works¶
Contrary to the FTDI converters, non-standard baudrates can't be directly requested when opening the port, but need to be stored in the EEPROM of the device, overwriting the default entries.
So it works like this: You open the port with a standard baudrate, the converter performs a look-up in the baudrate-table of its EEPROM and uses the non-standard mapping you programmed.
If you have a Pirelli DP-L10 you don't need to continue, the CP2102 in the phone has those mappings already preprogrammed.
Programming non-standard mappings¶
First of all you need to install the latest version of cp210x-program, an open-source tool replacing the proprietary windows-only tool from SiLabs (see application note AN205 if you want to mess with that). This can be done using the Python's package manager:
sudo pip install git+https://github.com/VCTLabs/cp210x-program.git
To make sure cp210x-program will be the only one talking to the converter, unload the kernel module:
sudo rmmod cp210x
After that, perform a dry-run to see everything is okay:
The tool should output the device-string of the converter, some other information, and a baudrate table with the following default entries:
[baudrate table] [...] 921600 = FFE6, FFF6, 1 # 923077 Baud, 20 us [...] 460800 = FFCC, FFEC, 1 # 461538 Baud, 40 us [...] 230400 = FF98, FFD9, 1 # 230769 Baud, 78 us [...] 115200 = FF30, FFB2, 1 # 115385 Baud, 156 us [...]
Okay, now to the real thing: create a backup of the EEPROM:
sudo cp210x-program -f eeprom.hex
The next step is to program the modified, non-standard baudrates:
sudo cp210x-program -p -F eeprom.hex -w --set-baudrate 812500:FFE2,FFF4,1 --set-baudrate 406250:FFC5,FFE9,1 --set-baudrate 203125:FF8A,FFD3,1
Check if the entries have been written successfully:
You should see the following entries:
[baudrate table] [...] 812500 = FFE2, FFF4, 1 # 800000 Baud, 24 us [...] 406250 = FFC5, FFE9, 1 # 406780 Baud, 46 us [...] 203125 = FF8A, FFD3, 1 # 203390 Baud, 90 us [...] 115200 = FF30, FFB2, 1 # 115385 Baud, 156 us [...]
Replug the converter and you're done.
If you want to use the burst_ind branch with a CP210x converter, you need to add the following define in osmocon.c: