Using DSP Units

I working with the Gowin GW1N devices and need to do some serious math. By
serious, I mean a number of calculations, not that they have to be fast.
In fact, I pretty much have all the time in the world relatively speaking.
The cycle time for performing all the calculations is 5 ms with a 33 MHz c
lock, so 167,000 odd cycles.
What I'm not up to speed about is just how to use or even infer such logic.
Certainly they can be instantiated which I might do. But the docs are pr
etty poor. For each configuration, the user guide shows a set of equations
it can implement, a block diagram with various control signals and data pa
ths and then an interface prototype of I suppose the inferred object. The
equations are very easy to understand...
DOUT = ?(A * B)
DOUT = A *
B + CASI
The full capability is more complex, but the copy and paste has too many th
ings to fix up to bother with. The point is they don't make it clear how t
he controls work or even what can be controlled in real time vs. needing to
be configured. I guess I'll have to write some code and experiment with t
he synthesis. I can try writing support for some answers. This is a perso
n rather than a black hole at a web site, so I usually get an adequate answ
er.
I just wondered how this is done with other brands of devices.
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Rick C. 

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gnuarm.deletethisbit
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By instantiation (in my case with Lattice or Altera), mainly because the DSP is avery limited resource and I needed full control over how it was shared. My one big Vivado project with a chip with much more resources I think I let the tools to a bit of inferring but mostly used blocks out of the Xilinx IP collection.
MK
Reply to
Michael Kellett
In the Xilinx tools, it's generally easy to infer your logic, and let the tools figure out how to place it in DSPs. I used to try to place pipeline registers where they were needed based on the DSP architecture, but soon found out that if you just place a lot of pipeline stages at the end, the tools will push the registers into the required places. If you were using 3rd party tools like Symplify Pro I would expect the same behavior regardless of the target FPGA. I'm not familiar with Gowin, so I couldn't tell you what to expect from their tools. In any case it's easy enough to write code for inference and see what the tools do with it.
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Gabor
Reply to
Gabor
By serious, I mean a number of calculations, not that they have to be fast . In fact, I pretty much have all the time in the world relatively speaking . The cycle time for performing all the calculations is 5 ms with a 33 MHz clock, so 167,000 odd cycles.
gic. Certainly they can be instantiated which I might do. But the docs are pretty poor. For each configuration, the user guide shows a set of equation s it can implement, a block diagram with various control signals and data p aths and then an interface prototype of I suppose the inferred object. The equations are very easy to understand...
y things to fix up to bother with. The point is they don't make it clear ho w the controls work or even what can be controlled in real time vs. needing to be configured. I guess I'll have to write some code and experiment with the synthesis. I can try writing support for some answers. This is a perso n rather than a black hole at a web site, so I usually get an adequate answ er.
I'd be willing to use inference if I actually could understand just what is in the DSP blocks. The adder can do addition or subtraction, but I can't tell if that is configurable at run time. There are various multiplexers a nd a variety of inputs to a rather large mux for the large accumulator, unc lear how to control that one. I guess I'll just have to ask if there is mo re documentation.
Thanks for the reply
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Rick C. 

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gnuarm.deletethisbit
e
I
.
Thanks for the reply. I tried inference and it seems to be using a separa te DSP unit for the multiply and for the add. Maybe I need to combine the two into a single assignment.
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Rick C. 

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gnuarm.deletethisbit
The IP tool lets you select a number of different operations selected by an input value. As I remember both the input adder and the output adder are dynamically configurable for adding or subtracting, but I would have to double check that (At least for the part I was using)
Reply to
Richard Damon
:
h. By serious, I mean a number of calculations, not that they have to be fa st. In fact, I pretty much have all the time in the world relatively speaki ng. The cycle time for performing all the calculations is 5 ms with a 33 MH z clock, so 167,000 odd cycles.
logic. Certainly they can be instantiated which I might do. But the docs ar e pretty poor. For each configuration, the user guide shows a set of equati ons it can implement, a block diagram with various control signals and data paths and then an interface prototype of I suppose the inferred object. Th e equations are very easy to understand...
any things to fix up to bother with. The point is they don't make it clear how the controls work or even what can be controlled in real time vs. needi ng to be configured. I guess I'll have to write some code and experiment wi th the synthesis. I can try writing support for some answers. This is a per son rather than a black hole at a web site, so I usually get an adequate an swer.
he
s
I
t is in the DSP blocks. The adder can do addition or subtraction, but I can 't tell if that is configurable at run time. There are various multiplexers and a variety of inputs to a rather large mux for the large accumulator, u nclear how to control that one. I guess I'll just have to ask if there is m ore documentation.
Yeah, I can't find where much is configurable in the application, rather th ere are parameters (generics) that establish connectivity and function. Bu t the docs don't really explain just what they do, only the number of bits occupied.
GENERIC ( AREG:bit:='0'; BREG:bit:='0'; ASIGN_REG:bit:='0'; BSIGN_REG:bit:='0'; ACCLOAD_REG:bit:='0'; OUT_REG:bit:='0'; B_ADD_SUB:bit:='0'; C_ADD_SUB:bit:='0'; ALUD_MODE:integer:=0; ALU_RESET_MODE:string:="SYNC" );
As far as I can tell the operations are fixed and there's no way to selecti vely add/subtract in real time. The ALU info seems to show a real time A a nd B sign input, but no real indication of what they do. The combined mult
e of the equations. Are the multiply and ALU functions separate DSP blocks or are both contained in every DSP block?
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Rick C. 

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gnuarm.deletethisbit
I tend to use the IP integrator to make a configured version of the DSP block, and that integrator lets you make a list of operations. I would need to try it to see if it allows both an add and a subtract selected by the 'operaiton' input to the module.
I haven't figured out the incantations to directly generate some of these blocks without using the IP integrator. I haven't found the documentations for that.
My understanding is that the whole block is one module, and at least on the part I am using they come in pairs that can be coupled to make a bigger block with a faster path for a partial sum from one block to another.
Reply to
Richard Damon

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