the name of the top entity in the wr_streamers folder was missleading
(xwr_transmission). It was recommended to rename, which I did.
Additionally, names of two modules in wr_streamers start with gc_
which could indicate they are general-cores. This is not the case,
moreover the entity names did not have gc_. I removed the gc_

- added DISABLED state to FSM to explicitely sit in DISABLED state
  when the mechanism is not enabled (before it was in reset/ALLOW)
- changed std_logic_vectors to unsigned in number of places, this
  made the code more readable and concise
- defined constants with zero latency (instead of having signal)
- added delay to latency calculation so that the latency introduced
  by gc_sync_ffs is accounted for

There was a number of processes that did something depending on a
state. The asynch-process was replaced with "when" statement.
The stuff done in separate synchronous processes are now done in
the same process as FSM

private package, or fabric_pkg in case of fabric sink/source

commit

this generics sets the operation mode of streamers (rx-only, tx-only
or rx_and_tx)

streamer.

- when instantiating wr_transmission (top streamers), it is now possible
  to define that only RX or only TX or both (RX and TX) streamers are used.
  this is to save resources and still use all the other goodies added to
  the streamers and also wrpc/wr-cores (this configuration will be
  propagated to the top of board entity in the next commit. So, the
  user can still use the board (and even ref-design) and instantiate
  only reception (or tranmission) to save resources
- the statistics entity is now split into 3 entities (top, rx, tx)

- BTrain requires to set more parameters than just tx/rx_data_width
- it would be messy to have all the parameters in the top of each board
- I made a record with all tx/rx parameters and replaced the currently
  existing two generics that reach the top of svec/spec/vfchd_board
  with these record.
- Now, all the tx/rx parameters of tx/rx streamers can be set when
  using the "board" top
- Default constant is used with default values (defined ine streamers pkg)
- it is planed to have constant with default parameters for BTrain as well
  in the BTrain package. Possibly, the same policy can be used for other
  applications

- made the tx and rx streamer symmetric in terms of seeting the
  buffer size, now both have proper generics
- added proper descriptions
- added sanity checks for generics
- set (hopefully) more sensible defults

- corrected name of f_dbg_word_starting_at_byte (byte->bit)
- expanded description of g_rx_data_width
- added descriptions of g_rx_data_width and g_tx_data_width the info
  that they are required to be multiples of 16 bits

bin: modfied wrpc-sw for simulations to not perform SDB discovery, in order to speed-up simulation time

built from wrpc-sw using commit:
91ab423 sim main: disable discovery of peripherals via SDB to speed-up the simulation.

rx/tx streamers generics/ports

Set RCV_TERM_VTTRX to false. Now Rx Termination mode 2 is selected and active, as advised in ug386 for GbE

Tunable SFP WRT-SFPPT015SC caused trouble in the SPEC (Link Down). The receive amplitude is only 920 mVpp.
The Spartan6 PHY settings for Rx Termination were not conform any mode (see Xilinx UG386 Table 4-4 to 4-7).

Compiled from commit 180419ee of wrpc-sw repo.

We can finally do this with the fix:
2974805 - top/vfchd: disable external reference support

Currently external reference channel doesn't work on vfc-hd, thus we disable it.

When external reference support was disabled, this was causing Altera-based
board (VFC-HD) never to generate valid timestamps for frames (pps-gen was never
producing pps_valid=1).