1 """ Pipeline and BufferedHandshake implementation, conforming to the same API.
2 For multi-input and multi-output variants, see multipipe.
7 a strategically very important function that is identical in function
8 to nmigen's Signal.eq function, except it may take objects, or a list
9 of objects, or a tuple of objects, and where objects may also be
15 stage requires compliance with a strict API that may be
16 implemented in several means, including as a static class.
17 the methods of a stage instance must be as follows:
19 * ispec() - Input data format specification
20 returns an object or a list or tuple of objects, or
21 a Record, each object having an "eq" function which
22 takes responsibility for copying by assignment all
24 * ospec() - Output data format specification
25 requirements as for ospec
26 * process(m, i) - Processes an ispec-formatted object
27 returns a combinatorial block of a result that
28 may be assigned to the output, by way of the "eq"
30 * setup(m, i) - Optional function for setting up submodules
31 may be used for more complex stages, to link
32 the input (i) to submodules. must take responsibility
33 for adding those submodules to the module (m).
34 the submodules must be combinatorial blocks and
35 must have their inputs and output linked combinatorially.
37 Both StageCls (for use with non-static classes) and Stage (for use
38 by static classes) are abstract classes from which, for convenience
39 and as a courtesy to other developers, anything conforming to the
40 Stage API may *choose* to derive.
45 A useful combinatorial wrapper around stages that chains them together
46 and then presents a Stage-API-conformant interface. By presenting
47 the same API as the stages it wraps, it can clearly be used recursively.
52 A convenience class that takes an input shape, output shape, a
53 "processing" function and an optional "setup" function. Honestly
54 though, there's not much more effort to just... create a class
55 that returns a couple of Records (see ExampleAddRecordStage in
61 A convenience class that takes a single function as a parameter,
62 that is chain-called to create the exact same input and output spec.
63 It has a process() function that simply returns its input.
65 Instances of this class are completely redundant if handed to
66 StageChain, however when passed to UnbufferedPipeline they
67 can be used to introduce a single clock delay.
72 The base class for pipelines. Contains previous and next ready/valid/data.
73 Also has an extremely useful "connect" function that can be used to
74 connect a chain of pipelines and present the exact same prev/next
80 A simple stalling clock-synchronised pipeline that has no buffering
81 (unlike BufferedHandshake). Data flows on *every* clock cycle when
82 the conditions are right (this is nominally when the input is valid
83 and the output is ready).
85 A stall anywhere along the line will result in a stall back-propagating
86 down the entire chain. The BufferedHandshake by contrast will buffer
87 incoming data, allowing previous stages one clock cycle's grace before
90 An advantage of the UnbufferedPipeline over the Buffered one is
91 that the amount of logic needed (number of gates) is greatly
92 reduced (no second set of buffers basically)
94 The disadvantage of the UnbufferedPipeline is that the valid/ready
95 logic, if chained together, is *combinatorial*, resulting in
96 progressively larger gate delay.
101 A Control class that introduces a single clock delay, passing its
102 data through unaltered. Unlike RegisterPipeline (which relies
103 on UnbufferedPipeline and PassThroughStage) it handles ready/valid
109 A convenience class that, because UnbufferedPipeline introduces a single
110 clock delay, when its stage is a PassThroughStage, it results in a Pipeline
111 stage that, duh, delays its (unmodified) input by one clock cycle.
116 nmigen implementation of buffered pipeline stage, based on zipcpu:
117 https://zipcpu.com/blog/2017/08/14/strategies-for-pipelining.html
119 this module requires quite a bit of thought to understand how it works
120 (and why it is needed in the first place). reading the above is
121 *strongly* recommended.
123 unlike john dawson's IEEE754 FPU STB/ACK signalling, which requires
124 the STB / ACK signals to raise and lower (on separate clocks) before
125 data may proceeed (thus only allowing one piece of data to proceed
126 on *ALTERNATE* cycles), the signalling here is a true pipeline
127 where data will flow on *every* clock when the conditions are right.
129 input acceptance conditions are when:
130 * incoming previous-stage strobe (p.i_valid) is HIGH
131 * outgoing previous-stage ready (p.o_ready) is LOW
133 output transmission conditions are when:
134 * outgoing next-stage strobe (n.o_valid) is HIGH
135 * outgoing next-stage ready (n.i_ready) is LOW
137 the tricky bit is when the input has valid data and the output is not
138 ready to accept it. if it wasn't for the clock synchronisation, it
139 would be possible to tell the input "hey don't send that data, we're
140 not ready". unfortunately, it's not possible to "change the past":
141 the previous stage *has no choice* but to pass on its data.
143 therefore, the incoming data *must* be accepted - and stored: that
144 is the responsibility / contract that this stage *must* accept.
145 on the same clock, it's possible to tell the input that it must
146 not send any more data. this is the "stall" condition.
148 we now effectively have *two* possible pieces of data to "choose" from:
149 the buffered data, and the incoming data. the decision as to which
150 to process and output is based on whether we are in "stall" or not.
151 i.e. when the next stage is no longer ready, the output comes from
152 the buffer if a stall had previously occurred, otherwise it comes
153 direct from processing the input.
155 this allows us to respect a synchronous "travelling STB" with what
156 dan calls a "buffered handshake".
158 it's quite a complex state machine!
163 Synchronised pipeline, Based on:
164 https://github.com/ZipCPU/dbgbus/blob/master/hexbus/rtl/hbdeword.v
167 from nmigen
import Signal
, Cat
, Const
, Mux
, Module
, Value
168 from nmigen
.cli
import verilog
, rtlil
169 from nmigen
.hdl
.ast
import ArrayProxy
170 from nmigen
.hdl
.rec
import Record
, Layout
172 from abc
import ABCMeta
, abstractmethod
173 from collections
.abc
import Sequence
177 """ contains signals that come *from* the previous stage (both in and out)
178 * i_valid: previous stage indicating all incoming data is valid.
179 may be a multi-bit signal, where all bits are required
180 to be asserted to indicate "valid".
181 * o_ready: output to next stage indicating readiness to accept data
182 * i_data : an input - added by the user of this class
185 def __init__(self
, i_width
=1, stage_ctl
=False):
186 self
.stage_ctl
= stage_ctl
187 self
.i_valid
= Signal(i_width
, name
="p_i_valid") # prev >>in self
188 self
._o
_ready
= Signal(name
="p_o_ready") # prev <<out self
189 self
.i_data
= None # XXX MUST BE ADDED BY USER
191 self
.s_o_ready
= Signal(name
="p_s_o_rdy") # prev <<out self
195 """ public-facing API: indicates (externally) that stage is ready
198 return self
.s_o_ready
# set dynamically by stage
199 return self
._o
_ready
# return this when not under dynamic control
201 def _connect_in(self
, prev
):
202 """ internal helper function to connect stage to an input source.
203 do not use to connect stage-to-stage!
205 return [self
.i_valid
.eq(prev
.i_valid_test
),
206 prev
.o_ready
.eq(self
.o_ready
),
207 eq(self
.i_data
, prev
.i_data
),
211 def i_valid_test(self
):
212 vlen
= len(self
.i_valid
)
214 # multi-bit case: valid only when i_valid is all 1s
215 all1s
= Const(-1, (len(self
.i_valid
), False))
216 i_valid
= (self
.i_valid
== all1s
)
218 # single-bit i_valid case
219 i_valid
= self
.i_valid
221 # when stage indicates not ready, incoming data
222 # must "appear" to be not ready too
224 i_valid
= i_valid
& self
.s_o_ready
230 """ contains the signals that go *to* the next stage (both in and out)
231 * o_valid: output indicating to next stage that data is valid
232 * i_ready: input from next stage indicating that it can accept data
233 * o_data : an output - added by the user of this class
235 def __init__(self
, stage_ctl
=False):
236 self
.stage_ctl
= stage_ctl
237 self
.o_valid
= Signal(name
="n_o_valid") # self out>> next
238 self
.i_ready
= Signal(name
="n_i_ready") # self <<in next
239 self
.o_data
= None # XXX MUST BE ADDED BY USER
241 self
.d_valid
= Signal(reset
=1) # INTERNAL (data valid)
244 def i_ready_test(self
):
246 return self
.i_ready
& self
.d_valid
249 def connect_to_next(self
, nxt
):
250 """ helper function to connect to the next stage data/valid/ready.
251 data/valid is passed *TO* nxt, and ready comes *IN* from nxt.
252 use this when connecting stage-to-stage
254 return [nxt
.i_valid
.eq(self
.o_valid
),
255 self
.i_ready
.eq(nxt
.o_ready
),
256 eq(nxt
.i_data
, self
.o_data
),
259 def _connect_out(self
, nxt
):
260 """ internal helper function to connect stage to an output source.
261 do not use to connect stage-to-stage!
263 return [nxt
.o_valid
.eq(self
.o_valid
),
264 self
.i_ready
.eq(nxt
.i_ready_test
),
265 eq(nxt
.o_data
, self
.o_data
),
270 """ makes signals equal: a helper routine which identifies if it is being
271 passed a list (or tuple) of objects, or signals, or Records, and calls
272 the objects' eq function.
274 complex objects (classes) can be used: they must follow the
275 convention of having an eq member function, which takes the
276 responsibility of further calling eq and returning a list of
279 Record is a special (unusual, recursive) case, where the input may be
280 specified as a dictionary (which may contain further dictionaries,
281 recursively), where the field names of the dictionary must match
282 the Record's field spec. Alternatively, an object with the same
283 member names as the Record may be assigned: it does not have to
286 ArrayProxy is also special-cased, it's a bit messy: whilst ArrayProxy
287 has an eq function, the object being assigned to it (e.g. a python
288 object) might not. despite the *input* having an eq function,
289 that doesn't help us, because it's the *ArrayProxy* that's being
290 assigned to. so.... we cheat. use the ports() function of the
291 python object, enumerate them, find out the list of Signals that way,
295 if isinstance(o
, dict):
296 for (k
, v
) in o
.items():
297 print ("d-eq", v
, i
[k
])
298 res
.append(v
.eq(i
[k
]))
301 if not isinstance(o
, Sequence
):
303 for (ao
, ai
) in zip(o
, i
):
304 #print ("eq", ao, ai)
305 if isinstance(ao
, Record
):
307 for idx
, (field_name
, field_shape
, _
) in enumerate(ao
.layout
):
308 if isinstance(field_shape
, Layout
):
312 if hasattr(val
, field_name
): # check for attribute
313 val
= getattr(val
, field_name
)
315 val
= val
[field_name
] # dictionary-style specification
316 rres
+= eq(ao
.fields
[field_name
], val
)
317 elif isinstance(ao
, ArrayProxy
) and not isinstance(ai
, Value
):
320 op
= getattr(ao
, p
.name
)
321 #print (op, p, p.name)
322 rres
.append(op
.eq(p
))
325 if not isinstance(rres
, Sequence
):
331 class StageCls(metaclass
=ABCMeta
):
332 """ Class-based "Stage" API. requires instantiation (after derivation)
334 see "Stage API" above.. Note: python does *not* require derivation
335 from this class. All that is required is that the pipelines *have*
336 the functions listed in this class. Derivation from this class
337 is therefore merely a "courtesy" to maintainers.
340 def ispec(self
): pass # REQUIRED
342 def ospec(self
): pass # REQUIRED
344 #def setup(self, m, i): pass # OPTIONAL
346 def process(self
, i
): pass # REQUIRED
349 class Stage(metaclass
=ABCMeta
):
350 """ Static "Stage" API. does not require instantiation (after derivation)
352 see "Stage API" above. Note: python does *not* require derivation
353 from this class. All that is required is that the pipelines *have*
354 the functions listed in this class. Derivation from this class
355 is therefore merely a "courtesy" to maintainers.
367 #def setup(m, i): pass
374 class RecordBasedStage(Stage
):
375 """ convenience class which provides a Records-based layout.
376 honestly it's a lot easier just to create a direct Records-based
377 class (see ExampleAddRecordStage)
379 def __init__(self
, in_shape
, out_shape
, processfn
, setupfn
=None):
380 self
.in_shape
= in_shape
381 self
.out_shape
= out_shape
382 self
.__process
= processfn
383 self
.__setup
= setupfn
384 def ispec(self
): return Record(self
.in_shape
)
385 def ospec(self
): return Record(self
.out_shape
)
386 def process(seif
, i
): return self
.__process
(i
)
387 def setup(seif
, m
, i
): return self
.__setup
(m
, i
)
390 class StageChain(StageCls
):
391 """ pass in a list of stages, and they will automatically be
392 chained together via their input and output specs into a
395 the end result basically conforms to the exact same Stage API.
397 * input to this class will be the input of the first stage
398 * output of first stage goes into input of second
399 * output of second goes into input into third (etc. etc.)
400 * the output of this class will be the output of the last stage
402 def __init__(self
, chain
, specallocate
=False):
404 self
.specallocate
= specallocate
407 return self
.chain
[0].ispec()
410 return self
.chain
[-1].ospec()
412 def _specallocate_setup(self
, m
, i
):
413 for (idx
, c
) in enumerate(self
.chain
):
414 if hasattr(c
, "setup"):
415 c
.setup(m
, i
) # stage may have some module stuff
416 o
= self
.chain
[idx
].ospec() # last assignment survives
417 m
.d
.comb
+= eq(o
, c
.process(i
)) # process input into "o"
418 if idx
== len(self
.chain
)-1:
420 i
= self
.chain
[idx
+1].ispec() # new input on next loop
421 m
.d
.comb
+= eq(i
, o
) # assign to next input
422 return o
# last loop is the output
424 def _noallocate_setup(self
, m
, i
):
425 for (idx
, c
) in enumerate(self
.chain
):
426 if hasattr(c
, "setup"):
427 c
.setup(m
, i
) # stage may have some module stuff
428 i
= o
= c
.process(i
) # store input into "o"
429 return o
# last loop is the output
431 def setup(self
, m
, i
):
432 if self
.specallocate
:
433 self
.o
= self
._specallocate
_setup
(m
, i
)
435 self
.o
= self
._noallocate
_setup
(m
, i
)
437 def process(self
, i
):
438 return self
.o
# conform to Stage API: return last-loop output
442 """ Common functions for Pipeline API
444 def __init__(self
, stage
=None, in_multi
=None, stage_ctl
=False):
445 """ Base class containing ready/valid/data to previous and next stages
447 * p: contains ready/valid to the previous stage
448 * n: contains ready/valid to the next stage
450 Except when calling Controlbase.connect(), user must also:
451 * add i_data member to PrevControl (p) and
452 * add o_data member to NextControl (n)
456 # set up input and output IO ACK (prev/next ready/valid)
457 self
.p
= PrevControl(in_multi
, stage_ctl
)
458 self
.n
= NextControl(stage_ctl
)
460 # set up the input and output data
461 if stage
is not None:
462 self
.p
.i_data
= stage
.ispec() # input type
463 self
.n
.o_data
= stage
.ospec()
465 def connect_to_next(self
, nxt
):
466 """ helper function to connect to the next stage data/valid/ready.
468 return self
.n
.connect_to_next(nxt
.p
)
470 def _connect_in(self
, prev
):
471 """ internal helper function to connect stage to an input source.
472 do not use to connect stage-to-stage!
474 return self
.p
._connect
_in
(prev
.p
)
476 def _connect_out(self
, nxt
):
477 """ internal helper function to connect stage to an output source.
478 do not use to connect stage-to-stage!
480 return self
.n
._connect
_out
(nxt
.n
)
482 def connect(self
, pipechain
):
483 """ connects a chain (list) of Pipeline instances together and
484 links them to this ControlBase instance:
486 in <----> self <---> out
489 [pipe1, pipe2, pipe3, pipe4]
492 out---in out--in out---in
494 Also takes care of allocating i_data/o_data, by looking up
495 the data spec for each end of the pipechain. i.e It is NOT
496 necessary to allocate self.p.i_data or self.n.o_data manually:
497 this is handled AUTOMATICALLY, here.
499 Basically this function is the direct equivalent of StageChain,
500 except that unlike StageChain, the Pipeline logic is followed.
502 Just as StageChain presents an object that conforms to the
503 Stage API from a list of objects that also conform to the
504 Stage API, an object that calls this Pipeline connect function
505 has the exact same pipeline API as the list of pipline objects
508 Thus it becomes possible to build up larger chains recursively.
509 More complex chains (multi-input, multi-output) will have to be
512 eqs
= [] # collated list of assignment statements
514 # connect inter-chain
515 for i
in range(len(pipechain
)-1):
517 pipe2
= pipechain
[i
+1]
518 eqs
+= pipe1
.connect_to_next(pipe2
)
520 # connect front of chain to ourselves
522 self
.p
.i_data
= front
.stage
.ispec()
523 eqs
+= front
._connect
_in
(self
)
525 # connect end of chain to ourselves
527 self
.n
.o_data
= end
.stage
.ospec()
528 eqs
+= end
._connect
_out
(self
)
532 def set_input(self
, i
):
533 """ helper function to set the input data
535 return eq(self
.p
.i_data
, i
)
538 res
= [self
.p
.i_valid
, self
.n
.i_ready
,
539 self
.n
.o_valid
, self
.p
.o_ready
,
541 if hasattr(self
.p
.i_data
, "ports"):
542 res
+= self
.p
.i_data
.ports()
545 if hasattr(self
.n
.o_data
, "ports"):
546 res
+= self
.n
.o_data
.ports()
551 def _elaborate(self
, platform
):
552 """ handles case where stage has dynamic ready/valid functions
555 if not self
.p
.stage_ctl
:
558 # intercept the previous (outgoing) "ready", combine with stage ready
559 m
.d
.comb
+= self
.p
.s_o_ready
.eq(self
.p
._o
_ready
& self
.stage
.d_ready
)
561 # intercept the next (incoming) "ready" and combine it with data valid
562 sdv
= self
.stage
.d_valid(self
.n
.i_ready
)
563 m
.d
.comb
+= self
.n
.d_valid
.eq(self
.n
.i_ready
& sdv
)
568 class BufferedHandshake(ControlBase
):
569 """ buffered pipeline stage. data and strobe signals travel in sync.
570 if ever the input is ready and the output is not, processed data
571 is shunted in a temporary register.
573 Argument: stage. see Stage API above
575 stage-1 p.i_valid >>in stage n.o_valid out>> stage+1
576 stage-1 p.o_ready <<out stage n.i_ready <<in stage+1
577 stage-1 p.i_data >>in stage n.o_data out>> stage+1
583 input data p.i_data is read (only), is processed and goes into an
584 intermediate result store [process()]. this is updated combinatorially.
586 in a non-stall condition, the intermediate result will go into the
587 output (update_output). however if ever there is a stall, it goes
588 into r_data instead [update_buffer()].
590 when the non-stall condition is released, r_data is the first
591 to be transferred to the output [flush_buffer()], and the stall
594 on the next cycle (as long as stall is not raised again) the
595 input may begin to be processed and transferred directly to output.
598 def elaborate(self
, platform
):
600 self
.m
= ControlBase
._elaborate
(self
, platform
)
602 result
= self
.stage
.ospec()
603 r_data
= self
.stage
.ospec()
604 if hasattr(self
.stage
, "setup"):
605 self
.stage
.setup(self
.m
, self
.p
.i_data
)
607 # establish some combinatorial temporaries
608 o_n_validn
= Signal(reset_less
=True)
609 n_i_ready
= Signal(reset_less
=True, name
="n_i_rdy_data")
610 i_p_valid_o_p_ready
= Signal(reset_less
=True)
611 p_i_valid
= Signal(reset_less
=True)
612 self
.m
.d
.comb
+= [p_i_valid
.eq(self
.p
.i_valid_test
),
613 o_n_validn
.eq(~self
.n
.o_valid
),
614 i_p_valid_o_p_ready
.eq(p_i_valid
& self
.p
.o_ready
),
615 n_i_ready
.eq(self
.n
.i_ready_test
),
618 # store result of processing in combinatorial temporary
619 self
.m
.d
.comb
+= eq(result
, self
.stage
.process(self
.p
.i_data
))
621 # if not in stall condition, update the temporary register
622 with self
.m
.If(self
.p
.o_ready
): # not stalled
623 self
.m
.d
.sync
+= eq(r_data
, result
) # update buffer
625 with self
.m
.If(n_i_ready
): # next stage is ready
626 with self
.m
.If(self
.p
._o
_ready
): # not stalled
627 # nothing in buffer: send (processed) input direct to output
628 self
.m
.d
.sync
+= [self
.n
.o_valid
.eq(p_i_valid
),
629 eq(self
.n
.o_data
, result
), # update output
631 with self
.m
.Else(): # p.o_ready is false, and data in buffer
632 # Flush the [already processed] buffer to the output port.
633 self
.m
.d
.sync
+= [self
.n
.o_valid
.eq(1), # reg empty
634 eq(self
.n
.o_data
, r_data
), # flush buffer
635 self
.p
._o
_ready
.eq(1), # clear stall
637 # ignore input, since p.o_ready is also false.
639 # (n.i_ready) is false here: next stage is ready
640 with self
.m
.Elif(o_n_validn
): # next stage being told "ready"
641 self
.m
.d
.sync
+= [self
.n
.o_valid
.eq(p_i_valid
),
642 self
.p
._o
_ready
.eq(1), # Keep the buffer empty
643 eq(self
.n
.o_data
, result
), # set output data
646 # (n.i_ready) false and (n.o_valid) true:
647 with self
.m
.Elif(i_p_valid_o_p_ready
):
648 # If next stage *is* ready, and not stalled yet, accept input
649 self
.m
.d
.sync
+= self
.p
._o
_ready
.eq(~
(p_i_valid
& self
.n
.o_valid
))
654 class SimpleHandshake(ControlBase
):
655 """ simple handshake control. data and strobe signals travel in sync.
656 implements the protocol used by Wishbone and AXI4.
658 Argument: stage. see Stage API above
660 stage-1 p.i_valid >>in stage n.o_valid out>> stage+1
661 stage-1 p.o_ready <<out stage n.i_ready <<in stage+1
662 stage-1 p.i_data >>in stage n.o_data out>> stage+1
667 def elaborate(self
, platform
):
669 self
.m
= ControlBase
._elaborate
(self
, platform
)
672 result
= self
.stage
.ospec()
673 if hasattr(self
.stage
, "setup"):
674 self
.stage
.setup(self
.m
, self
.p
.i_data
)
676 # establish some combinatorial temporaries
677 n_i_ready
= Signal(reset_less
=True, name
="n_i_rdy_data")
678 p_i_valid_p_o_ready
= Signal(reset_less
=True)
679 p_i_valid
= Signal(reset_less
=True)
680 self
.m
.d
.comb
+= [p_i_valid
.eq(self
.p
.i_valid_test
),
681 n_i_ready
.eq(self
.n
.i_ready_test
),
682 p_i_valid_p_o_ready
.eq(p_i_valid
& self
.p
.o_ready
),
685 # store result of processing in combinatorial temporary
686 self
.m
.d
.comb
+= eq(result
, self
.stage
.process(self
.p
.i_data
))
688 # previous valid and ready
689 with self
.m
.If(p_i_valid_p_o_ready
):
690 self
.m
.d
.sync
+= [r_busy
.eq(1), # output valid
691 #self.n.o_valid.eq(1), # output valid
692 eq(self
.n
.o_data
, result
), # update output
694 # previous invalid or not ready, however next is accepting
695 with self
.m
.Elif(n_i_ready
):
696 self
.m
.d
.sync
+= [ eq(self
.n
.o_data
, result
)]
697 # TODO: could still send data here (if there was any)
698 #self.m.d.sync += self.n.o_valid.eq(0) # ...so set output invalid
699 self
.m
.d
.sync
+= r_busy
.eq(0) # ...so set output invalid
701 self
.m
.d
.comb
+= self
.n
.o_valid
.eq(r_busy
)
702 # if next is ready, so is previous
703 self
.m
.d
.comb
+= self
.p
._o
_ready
.eq(n_i_ready
)
708 class UnbufferedPipeline(ControlBase
):
709 """ A simple pipeline stage with single-clock synchronisation
710 and two-way valid/ready synchronised signalling.
712 Note that a stall in one stage will result in the entire pipeline
715 Also that unlike BufferedHandshake, the valid/ready signalling does NOT
716 travel synchronously with the data: the valid/ready signalling
717 combines in a *combinatorial* fashion. Therefore, a long pipeline
718 chain will lengthen propagation delays.
720 Argument: stage. see Stage API, above
722 stage-1 p.i_valid >>in stage n.o_valid out>> stage+1
723 stage-1 p.o_ready <<out stage n.i_ready <<in stage+1
724 stage-1 p.i_data >>in stage n.o_data out>> stage+1
732 p.i_data : StageInput, shaped according to ispec
734 p.o_data : StageOutput, shaped according to ospec
736 r_data : input_shape according to ispec
737 A temporary (buffered) copy of a prior (valid) input.
738 This is HELD if the output is not ready. It is updated
740 result: output_shape according to ospec
741 The output of the combinatorial logic. it is updated
742 COMBINATORIALLY (no clock dependence).
745 def elaborate(self
, platform
):
746 self
.m
= ControlBase
._elaborate
(self
, platform
)
748 data_valid
= Signal() # is data valid or not
749 r_data
= self
.stage
.ispec() # input type
750 if hasattr(self
.stage
, "setup"):
751 self
.stage
.setup(self
.m
, r_data
)
754 p_i_valid
= Signal(reset_less
=True)
755 pv
= Signal(reset_less
=True)
756 self
.m
.d
.comb
+= p_i_valid
.eq(self
.p
.i_valid_test
)
757 self
.m
.d
.comb
+= pv
.eq(self
.p
.i_valid
& self
.p
.o_ready
)
759 self
.m
.d
.comb
+= self
.n
.o_valid
.eq(data_valid
)
760 self
.m
.d
.comb
+= self
.p
._o
_ready
.eq(~data_valid | self
.n
.i_ready_test
)
761 self
.m
.d
.sync
+= data_valid
.eq(p_i_valid | \
762 (~self
.n
.i_ready_test
& data_valid
))
764 self
.m
.d
.sync
+= eq(r_data
, self
.p
.i_data
)
765 self
.m
.d
.comb
+= eq(self
.n
.o_data
, self
.stage
.process(r_data
))
769 class UnbufferedPipeline2(ControlBase
):
770 """ A simple pipeline stage with single-clock synchronisation
771 and two-way valid/ready synchronised signalling.
773 Note that a stall in one stage will result in the entire pipeline
776 Also that unlike BufferedHandshake, the valid/ready signalling does NOT
777 travel synchronously with the data: the valid/ready signalling
778 combines in a *combinatorial* fashion. Therefore, a long pipeline
779 chain will lengthen propagation delays.
781 Argument: stage. see Stage API, above
783 stage-1 p.i_valid >>in stage n.o_valid out>> stage+1
784 stage-1 p.o_ready <<out stage n.i_ready <<in stage+1
785 stage-1 p.i_data >>in stage n.o_data out>> stage+1
793 p.i_data : StageInput, shaped according to ispec
795 p.o_data : StageOutput, shaped according to ospec
797 buf : output_shape according to ospec
798 A temporary (buffered) copy of a valid output
799 This is HELD if the output is not ready. It is updated
803 def elaborate(self
, platform
):
804 self
.m
= ControlBase
._elaborate
(self
, platform
)
806 buf_full
= Signal() # is data valid or not
807 buf
= self
.stage
.ospec() # output type
808 if hasattr(self
.stage
, "setup"):
809 self
.stage
.setup(self
.m
, self
.p
.i_data
)
812 p_i_valid
= Signal(reset_less
=True)
813 self
.m
.d
.comb
+= p_i_valid
.eq(self
.p
.i_valid_test
)
815 self
.m
.d
.comb
+= self
.n
.o_valid
.eq(buf_full | p_i_valid
)
816 self
.m
.d
.comb
+= self
.p
._o
_ready
.eq(~buf_full
)
817 self
.m
.d
.sync
+= buf_full
.eq(~self
.n
.i_ready_test
& self
.n
.o_valid
)
819 odata
= Mux(buf_full
, buf
, self
.stage
.process(self
.p
.i_data
))
820 self
.m
.d
.comb
+= eq(self
.n
.o_data
, odata
)
821 self
.m
.d
.sync
+= eq(buf
, self
.n
.o_data
)
826 class PassThroughStage(StageCls
):
827 """ a pass-through stage which has its input data spec equal to its output,
828 and "passes through" its data from input to output.
830 def __init__(self
, iospecfn
):
831 self
.iospecfn
= iospecfn
832 def ispec(self
): return self
.iospecfn()
833 def ospec(self
): return self
.iospecfn()
834 def process(self
, i
): return i
837 class PassThroughHandshake(ControlBase
):
838 """ A control block that delays by one clock cycle.
841 def elaborate(self
, platform
):
842 m
= ControlBase
._elaborate
(self
, platform
)
845 p_i_valid
= Signal(reset_less
=True)
846 pvr
= Signal(reset_less
=True)
847 m
.d
.comb
+= p_i_valid
.eq(self
.p
.i_valid_test
)
848 m
.d
.comb
+= pvr
.eq(p_i_valid
& self
.p
.o_ready
)
850 m
.d
.comb
+= self
.p
.o_ready
.eq(~self
.n
.o_valid | self
.n
.i_ready_test
)
851 m
.d
.sync
+= self
.n
.o_valid
.eq(p_i_valid | ~self
.p
.o_ready
)
853 odata
= Mux(pvr
, self
.stage
.process(self
.p
.i_data
), self
.n
.o_data
)
854 m
.d
.sync
+= eq(self
.n
.o_data
, odata
)
860 class RegisterPipeline(UnbufferedPipeline
):
861 """ A pipeline stage that delays by one clock cycle, creating a
862 sync'd latch out of o_data and o_valid as an indirect byproduct
863 of using PassThroughStage
865 def __init__(self
, iospecfn
):
866 UnbufferedPipeline
.__init
__(self
, PassThroughStage(iospecfn
))