Hi Paul, Thanks for the link. I looked through the code a bit and it doesn't seem as though the "corr" library at all. Have I been using the wrong tool for the job?
Would you be able to point me to which file I should start with to get a handle on how the casperfpga package works? Regards, James On Fri, Mar 20, 2015 at 9:22 AM, Paul Prozesky <[email protected]> wrote: > Morning James > > We do this in already in the casperfpga package: > https://github.com/ska-sa/casperfpga > > It turns out construct is pretty slow, so we just do the conversions and > shifts manually. I think currently the fpg files that are automatically > parsed by casperfpga are only generated for ROACH2, but it would be easy to > add ROACH support. > > Cheers > Paul > > > > > On 20 March 2015 at 09:08, James Smith <[email protected]> wrote: > >> Hello all, >> >> I've given some thought to the topic of writing (and reading) registers >> on the ROACH using the python corr module. Often in a design a single >> register may be sliced into many bits to control various things. The way >> I've normally seen such a register written in python looks something like >> this: >> >> fpga.write_int('control',1<<9|1<<10|0<<25|1<<2|1<<3) >> >> My feeling is that this approach is difficult to maintain - inheriting >> code from someone else (or even from one's self 6 months down the line) is >> likely to bring about some confusion in this case, and lead to a fair >> amount of spelunking through the Simulink model in order to figure out what >> bit 9 and bit 10 etc. do. On top of this, it places limitations on changing >> one of the bits later without modifying the other ones - bitwise or >> functions work well enough when you're over-writing zeros, but if there's >> something there already it might not work so well. >> >> With this in mind, I would like to suggest a convention which I worked >> out. It uses python modules "struct" and "construct" to make code a bit >> easier to read. >> (For reference if anyone is unfamiliar: >> struct - https://docs.python.org/2/library/struct.html >> construct - http://construct.readthedocs.org/en/latest/ ) >> >> In the design I'm working on at the moment (a wideband spectrometer), I >> wrote a python module with the following in it: >> >> # Bitstruct to control the control register on the ROACH >> control_reg_bitstruct = construct.BitStruct('control_reg', >> construct.Padding(4), #28-31 >> construct.BitField('debug_snap_select',3), #25-27 >> construct.Padding(3), #22-24 >> construct.Flag('fine_tvg_en'), #21 >> construct.Flag('adc_tvg'), #20 >> construct.Flag('fd_fs_tvg'), #19 >> construct.Flag('packetiser_tvg'), #18 >> construct.Flag('ct_tvg'), #17 >> construct.Flag('tvg_en'), #16 >> construct.Padding(4), #12-15 >> construct.Flag('fancy_en'), #11 >> construct.Flag('adc_protect_disable'), #10 >> construct.Flag('gbe_enable'), #09 >> construct.Flag('gbe_rst'), #08 >> construct.Padding(4), #04-07 >> construct.Flag('clr_status'), #03 >> construct.Flag('arm'), #02 >> construct.Flag('man_sync'), #01 >> construct.Flag('sys_rst') ) #00 >> >> This BitStruct makes the code a little bit more readable, tells you what >> each bit does, and if you've done this declaration right once, then you >> don't need to worry about whether you'e shifting numbers by the right >> amount of bits. For the BitFields where several bits are passed, I used a >> dictionary to make remembering things (and reading the code) easier as well: >> >> # Dictionary for selecting the debug_snap_select bit >> debug_snap_select = { >> 'coarse_72': 0, >> 'fine_128': 1, >> 'quant_16': 2, >> 'ct_64': 3, >> 'xaui_128': 4, >> 'gbetx0_128': 5, >> 'buffer_72': 6, >> 'finepfb_72': 7 } >> >> So writing to the register for the first time works like this: >> >> control_reg = avn.control_reg_bitstruct.parse('\x00\x00\x00\x00') # >> Create a blank one to use... >> # Pulse arm and clr_status high, along with setting gbe_enable and >> adc_protect_disable high >> control_reg.gbe_enable = True >> control_reg.adc_protect_disable = True >> control_reg.clr_status = True >> control_reg.arm = True >> fpga.write_int('control', struct.unpack('>I', >> avn.control_reg_bitstruct.build(control_reg))[0]) # The [0] is necessary >> because the fpga.write_int function wants an integer datatype, and >> struct.unpack returns a tuple for some reason. >> # Bring arm and clr_status low again. >> control_reg.clr_status = False >> control_reg.arm = False >> fpga.write_int('control', >> struct.unpack('>I',avn.control_reg_bitstruct.build(control_reg))[0]) >> >> Then, for example if you're controlling something with a function and you >> need to change only one part of what's in the register and leave the rest >> unaffected, this is quite easy as well: >> >> control_reg = >> control_reg_bitstruct.parse(struct.pack('>I',fpga.read_uint('control'))) # >> Read the data that's in the register already >> control_reg.debug_snap_select = debug_snap_select['coarse_72'] # >> Update the desired bit (or bits, using the conveniently provided dictionary >> in this case) >> fpga.write_int('control', struct.unpack('>I', >> control_reg_bitstruct.build(control_reg))[0]) # Write the new data back. >> >> Does anyone have any thoughts? Would this perhaps help with >> maintainability and debugging, or is it a bit of overkill, solving a >> problem that wasn't really there in the first place? I'm eager to hear any >> feedback from others who may have walked this path before. >> >> I've formatted the python code portions of the above message to a >> fixed-width font, I hope it comes through on the mailing list... >> >> Regards, >> James Smith >> >> >> >
