added Notes on RBF files for Uniboard2

libraries/io/epcs/doc/README.txt

+Notes on .RBF files on UniBoard2
+--------------------------------
+
+Thu Apr 21 14:44:02 CEST 2016
+
+
+For now it is assumed that .RBF files for a single design are not larger than 40Mbyte.
+Because the .SOF files are sized ~ 37Mbyte. But in the future it could be that 40Mbyte is not correct.
+
+For now (40Mbyte), the following start addresses are choosen (see python scripts pi_epcs.py and pi_remu.py)
+
+  Factory: 0
+  User:    41943040 (decimal)
+
+
+The EPCQL1024 flash has a capacity of 128M, so there is place for a 2nd User image.
+
+
+
+To boot the FPGA with a factory image (address 0) an extra bootloader is required
+This bootloader looks like (hexdump):
+
+
+  0000000 ffff ffff ffff ffff ffff ffff 6a6a 6a6a
+  0000010 0020 0000 0a03 0420 0420 0420 ffff 87fe
+
+
+Then the FPGA image starts at address offset 0x20:
+
+
+  0000020 a65c 0001 0004 0000 ffff ffff ffff ffff
+  0000030 ffff ffff ffff ffff ffff ffff ffff ffff
+  *
+  00000a0 959b 3d24 0000 0001 0001 0101 0100 0100
+  ...
+
+
+
+This means that The Factory .RBF file needs this bootloader and the User .RBF not.
+To generate the .RBF files (from .SOF), use the following commands:
+
+Factory .RBF (including bootloader):
+
+  echo "Bitstream_compression=on" > ${HOME}/.run_rbf_temp_options_file
+  quartus_cpf -d EPCQL1024 -m ASx4 --option=${HOME}/.run_rbf_temp_options_file -c design_name.sof design_name.pof
+  quartus_cpf -c design_name.pof design_name.hexout
+  nios2-elf-objcopy -I ihex -O binary design_name.hexout design_name.rbf
+  truncate -s 40M design_name.rbf
+
+User .RBF (excluding bootloader):
+
+  echo "Bitstream_compression=on" > ${HOME}/.run_rbf_temp_options_file
+  quartus_cpf -c --option=${HOME}/.run_rbf_temp_options_file design_name.sof design_name.rbf
+
+
+
+
+These commands are already included in the 'run_rbf' shell script.
+So to add the bootloader it takes more steps, as shown above. .POF files do include the bootloader, thats why the steps
+.SOF -> .POF -> .HEXOUT -> .RBF   are taken.
+
+To run the 'run_rbf' script:
+  run_rbf unb2a --unb2_factory design_name    # <- this adds the bootloader for the factory image
+  run_rbf unb2a design_name                   # <- no bootloader added (default)
+