2013-04-16

SDR API requirement specification


Recently I posted 2nd RFC of Kernel SDR API requirements. Currently I am performing some tests (Mirics FlexiTV SDR) how it could be integrated to the V4L2 API.

Here is current view of implementation control flow, listed in order from device to application:
  • Kernel device driver
    • controls device
  • Kernel V4L2 API
    • Kernel - user-space interface
  •  libv4l
    • existing library for applications
    • covers API from applications
    • makes raw format conversions to well known formats 

LINUX KERNEL SDR API REQUIREMENT SPECIFICATION

LINUX KERNEL SDR API REQUIREMENT SPECIFICATION
=====================================================================


Ideal SDR specific requirements (basics SDR settings)
*********************************************************************

operation mode
*  values: ADC (Rx) or DAC (Tx)
*  operations
     GET, inquire what HW supports
     GET, get current value
     SET, set desired value

sampling resolution
*  values: 1 - 32 (unit: bit)
     16 bit could be enough, but better to leave some room for future
*  operations
     GET, inquire what HW supports
     GET, get current value
     SET, set desired value

sampling rate
*  values: 1 - infinity (unit: Hz, symbols per second)
     currently 500 MHz is more than enough
*  operations
     GET, inquire what HW supports
     GET, get current value
     SET, set desired value

TODO:
*  inversion?


Practical SDR specific requirements (SDR settings for RF tuner)
*********************************************************************

RF frequency
*  values: 1 - infinity (unit: Hz)
     currently 100 GHz is more than enough
*  operations
     GET, inquire what HW supports
       there could be unsupported ranges between lower and upper freq
     GET, get current value
     SET, set desired value

IF frequency (intermediate frequency)
*  values: 0 - infinity (unit: Hz)
     currently 500 MHz is more than enough
*  operations
     GET, get current value

tuner lock (frequency synthesizer / PLL)
*  values: yes/no
*  operations
     GET, get current value

tuner gains
*  gain and attenuation
*  there could be multiple places to adjust gain on tuner signal path
*  is single overall gain enough or do we want more manual fine tuning?

tuner filters
*  there could be multiple filters on tuner signal path (RF/IF)
*  do we need to control filters at all?
*  calculate from sampling rate?


TODO:
*  pass RF standard to tuner?
   Passing standard is clearly against idea, but some RF tuners does
   "black magic" according to standard. That magic is usually setting
   filters and and gains, but it could be more...

*  inversion?


Hardware specific requirements (board settings)
*********************************************************************

antenna switch
*  values: 0 - 32 (unit: piece)
*  operations
     GET, inquire what HW supports
     GET, get current value
     SET, set desired value

external LNA
*  values: -200000 - 200000 (unit: dB/1000)
*  operations
     GET, inquire what HW supports
     GET, get current value
     SET, set desired value
* range from -200dB to 200dB should be enough

multiple ADCs / DACs on single device
*  there could be multiple ADCs and DACs on single device
*  resources could be shared which limits concurrent usage
*  eg. device has 2 ADC + 2 DAC = 4 total, but only 2 could be used
   at the time


Kernel specific requirements
*********************************************************************

device locking between multiple APIs
*  same device could support multiple APIs which could not be used at
   same time
*  for example DVB API and V4L2 API
*  locking needed


DOCUMENT VERSION HISTORY
=====================================================================
2012-10-15 Antti Palosaari <crope@iki.fi>
* Initial version

2013-04-11 Antti Palosaari <crope@iki.fi>
* add version history
* order requirements per sections
* add IF frequency (intermediate frequency)
* add tuner lock (frequency synthesizer / PLL)
* add external LNA
* add TODOs

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