-class NextControl:
- """ contains the signals that go *to* the next stage (both in and out)
- * o_valid: output indicating to next stage that data is valid
- * i_ready: input from next stage indicating that it can accept data
- * o_data : an output - added by the user of this class
- """
- def __init__(self):
- self.o_valid = Signal(name="n_o_valid") # out>>
- self.i_ready = Signal(name="n_i_ready") # <<in
-
- def connect_to_next(self, nxt):
- """ helper function to connect to the next stage data/valid/ready.
- data/valid is passed *TO* nxt, and ready comes *IN* from nxt.
- """
- return [nxt.i_valid.eq(self.o_valid),
- self.i_ready.eq(nxt.o_ready),
- eq(nxt.i_data, self.o_data),
- ]
-
- def connect_out(self, nxt):
- """ helper function to connect stage to an output source. do not
- use to connect stage-to-stage!
- """
- return [nxt.o_valid.eq(self.o_valid),
- self.i_ready.eq(nxt.i_ready),
- eq(nxt.o_data, self.o_data),
- ]
-
-
-def eq(o, i):
- """ makes signals equal: a helper routine which identifies if it is being
- passsed a list (or tuple) of objects, and calls the objects' eq
- function.
- """
- if not isinstance(o, Sequence):
- o, i = [o], [i]
- res = []
- for (ao, ai) in zip(o, i):
- res.append(ao.eq(ai))
- return res
-
-
-class PipelineBase:
- """ Common functions for Pipeline API
- """
- def __init__(self, stage):
- """ pass in a "stage" which may be either a static class or a class
- instance, which has three functions:
- * ispec: returns input signals according to the input specification
- * ispec: returns output signals to the output specification
- * process: takes an input instance and returns processed data
-
- User must also:
- * add i_data member to PrevControl and
- * add o_data member to NextControl
- """
- self.stage = stage
-
- # set up input and output IO ACK (prev/next ready/valid)
- self.p = PrevControl()
- self.n = NextControl()
-
- def connect_to_next(self, nxt):
- """ helper function to connect to the next stage data/valid/ready.
- """
- return self.n.connect_to_next(nxt.p)
-
- def connect_in(self, prev):
- """ helper function to connect stage to an input source. do not
- use to connect stage-to-stage!
- """
- return self.p.connect_in(prev.p)
-
- def connect_out(self, nxt):
- """ helper function to connect stage to an output source. do not
- use to connect stage-to-stage!
- """
- return self.n.connect_out(nxt.n)
-
- def set_input(self, i):
- """ helper function to set the input data
- """
- return eq(self.p.i_data, i)
-
- def ports(self):
- return [self.p.i_valid, self.n.i_ready,
- self.n.o_valid, self.p.o_ready,
- self.p.i_data, self.n.o_data # XXX need flattening!
- ]
-
-
-class BufferedPipeline(PipelineBase):
- """ buffered pipeline stage. data and strobe signals travel in sync.
- if ever the input is ready and the output is not, processed data
- is stored in a temporary register.
-
- stage-1 p.i_valid >>in stage n.o_valid out>> stage+1
- stage-1 p.o_ready <<out stage n.i_ready <<in stage+1
- stage-1 p.i_data >>in stage n.o_data out>> stage+1
- | |
- process --->----^
- | |
- +-- r_data ->-+
-
- input data p.i_data is read (only), is processed and goes into an
- intermediate result store [process()]. this is updated combinatorially.
-
- in a non-stall condition, the intermediate result will go into the
- output (update_output). however if ever there is a stall, it goes
- into r_data instead [update_buffer()].
-
- when the non-stall condition is released, r_data is the first
- to be transferred to the output [flush_buffer()], and the stall
- condition cleared.
-
- on the next cycle (as long as stall is not raised again) the
- input may begin to be processed and transferred directly to output.
- """
- def __init__(self, stage):
- PipelineBase.__init__(self, stage)
-
- # set up the input and output data
- self.p.i_data = stage.ispec() # input type
- self.n.o_data = stage.ospec()
-
- def elaborate(self, platform):
- m = Module()
-
- result = self.stage.ospec()
- r_data = self.stage.ospec()
- if hasattr(self.stage, "setup"):
- self.stage.setup(m, self.p.i_data)
-
- # establish some combinatorial temporaries
- o_n_validn = Signal(reset_less=True)
- i_p_valid_o_p_ready = Signal(reset_less=True)
- m.d.comb += [o_n_validn.eq(~self.n.o_valid),
- i_p_valid_o_p_ready.eq(self.p.i_valid & self.p.o_ready),
- ]
-
- # store result of processing in combinatorial temporary
- #with m.If(self.p.i_valid): # input is valid: process it
- m.d.comb += eq(result, self.stage.process(self.p.i_data))
- # if not in stall condition, update the temporary register
- with m.If(self.p.o_ready): # not stalled
- m.d.sync += eq(r_data, result) # update buffer
-
- #with m.If(self.p.i_rst): # reset
- # m.d.sync += self.n.o_valid.eq(0)
- # m.d.sync += self.p.o_ready.eq(0)
- with m.If(self.n.i_ready): # next stage is ready
- with m.If(self.p.o_ready): # not stalled
- # nothing in buffer: send (processed) input direct to output
- m.d.sync += [self.n.o_valid.eq(self.p.i_valid),
- eq(self.n.o_data, result), # update output
- ]
- with m.Else(): # p.o_ready is false, and something is in buffer.
- # Flush the [already processed] buffer to the output port.
- m.d.sync += [self.n.o_valid.eq(1),
- eq(self.n.o_data, r_data), # flush buffer
- # clear stall condition, declare register empty.
- self.p.o_ready.eq(1),
- ]
- # ignore input, since p.o_ready is also false.
-
- # (n.i_ready) is false here: next stage is ready
- with m.Elif(o_n_validn): # next stage being told "ready"
- m.d.sync += [self.n.o_valid.eq(self.p.i_valid),
- self.p.o_ready.eq(1), # Keep the buffer empty
- # set the output data (from comb result)
- eq(self.n.o_data, result),
- ]
- # (n.i_ready) false and (n.o_valid) true:
- with m.Elif(i_p_valid_o_p_ready):
- # If next stage *is* ready, and not stalled yet, accept input
- m.d.sync += self.p.o_ready.eq(~(self.p.i_valid & self.n.o_valid))
-
- return m