add G.709 codec

do/do_g709.do

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+onerror {resume}
+
+set incdir  ../include
+set rtldir  ../rtl
+set tbdir   ../testbench
+set workdir ../work
+#
+vlib $workdir
+#
+vlog -work $workdir -incr -sv +incdir+$incdir+$rtldir $rtldir/bch/*.sv
+vlog -work $workdir -incr -sv +incdir+$incdir+$rtldir $rtldir/rs/*.sv
+vlog -work $workdir -incr -sv +incdir+$incdir+$rtldir/g709 $rtldir/g709/*.sv
+
+vlog -work $workdir +initreg+0 -sv +incdir+$incdir+$tbdir/g709 $tbdir/g709/bertest.sv
+
+set seed [clock seconds]
+
+vsim -sv_seed $seed bertest -lib $workdir
+run -all

rtl/g709/README.md

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+ITU-T G.709 FEC realization
+
+vivado 2020.2 Kintex 7 - 2 
+
+Encoder: 	
+
+LUT/REG	~2.4k/~2.3k	> 250MHz ( > 32Gbps)
+
+Decoder: 
+
+LUT/REG/RAM ~18.8K/~15.1K/10    > 250MHz ( > 32Gbps) 
+
+Attention: The coder and decoder correspond each other but can have different bit order with standard codes.
+
+Decoder don't use RS code decfail decision. If decfail occured it sends incorrect bit fix to output. Change it if needed. 
+
+