applets.interface.better_la: better performance

this implements dynamic priority based scheduling in the LAArbiter.
Also it does improvements on the host-side python

Author: anuejn

software/glasgow/applet/interface/better_la/__init__.py

@@ -1,4 +1,5 @@
 from collections import defaultdict
+import io
 import logging
 import argparse
 from vcd import VCDWriter
@@ -9,27 +10,49 @@
 from ....gateware.analyzer import *
 from ... import *
 from .signal_compressor import SignalCompressor
-from .arbeiter import LAArbeiter
-
-# This LA uses a simple protocol for sending compressed values over the FIFO:
-# Each packet starts with a 8 bit size word. The size can be 0, then the word only consists of that
-# word. If the size is n != 0, the packet is n*2 bytes long. Each 16bit word is encoded acording
-# to the format described in the SignalCompressor value. The packets are round-robin for each pin.
+from .arbiter import LAarbiter
+
+# This LA uses a simple protocol for sending compressed values over the FIFO which is explained
+# in the arbiter.py (high level chunks) and signal_compressor.py (low level packets) files.
+# The basic architecture is as follows:
+#          +------------------+       +--------+
+# Pin0 --->| SignalCompressor |------>|  FIFO  |-----+
+#          +------------------+       +--------+     |
+#                                                    |
+#          +------------------+       +--------+     |
+# Pin1 --->| SignalCompressor |------>|  FIFO  |-----+     +-----------+      +----------+
+#          +------------------+       +--------+     |     |           |      |          |
+#                                                    +---->| LAArbiter |----->| USB-FIFO |
+#          +------------------+       +--------+     |     |           |      |          |
+# Pin2 --->| SignalCompressor |------>|  FIFO  |-----+     +-----------+      +----------+
+#          +------------------+       +--------+     |
+#                                                    |
+#          +------------------+       +--------+     |
+# PinN --->|       ...        |------>|   ...  |-----+
+#          +------------------+       +--------+
 
 class BetterLASubtarget(Elaboratable):
-    def __init__(self, pads, in_fifo):
+    def __init__(self, pads, in_fifo, counter_target=False):
         self.pads    = pads
         self.in_fifo = in_fifo
+        self.counter_target = counter_target
 
-        self.la = LAArbeiter(in_fifo)
+        self.la = LAarbiter(in_fifo)
 
     def elaborate(self, platform):
         m = Module()
         m.submodules += self.la
 
-        pins_i = Signal.like(self.pads.i_t.i)
-        m.submodules += FFSynchronizer(self.pads.i_t.i, pins_i)
-        m.d.comb += self.la.input.eq(pins_i)
+        if self.counter_target:
+            print("building bitstream with simulated counter target")
+            counter = Signal(len(self.pads.i_t.i)+2)
+            m.d.sync += counter.eq(counter + 1)
+            m.d.comb += self.la.input.eq(counter[2:])
+        else:
+            print("building bitstream connected to real target")
+            pins_i = Signal.like(self.pads.i_t.i)
+            m.submodules += FFSynchronizer(self.pads.i_t.i, pins_i)
+            m.d.comb += self.la.input.eq(pins_i)
 
         return m
 
@@ -46,12 +69,17 @@ def add_build_arguments(cls, parser, access):
         super().add_build_arguments(parser, access)
 
         access.add_pin_set_argument(parser, "i", width=range(1, 17), default=1)
+        parser.add_argument(
+            "--counter-target", default=False, action="store_true",
+            help="simulate a target with a counter signal",
+        )
 
     def build(self, target, args):
         self.mux_interface = iface = target.multiplexer.claim_interface(self, args)
         iface.add_subtarget(BetterLASubtarget(
             pads=iface.get_pads(args, pin_sets=("i",)),
-            in_fifo=iface.get_in_fifo(depth=512*16),
+            in_fifo=iface.get_in_fifo(depth=512*16, auto_flush=False),
+            counter_target=args.counter_target
         ))
 
         self._sample_freq = target.sys_clk_freq
@@ -85,53 +113,76 @@ def add_interact_arguments(cls, parser):
         parser.add_argument(
             "file", metavar="VCD-FILE", type=argparse.FileType("w"),
             help="write VCD waveforms to VCD-FILE")
+        parser.add_argument("--buffer-size", type=int, default=10,
+                            help="how much data to capture in MB")
 
     async def interact(self, device, args, iface):
-        pins = defaultdict(list)
-        overrun = False
-
-        zero_chunks = 0
-        chunks = 0
-        try:  # this try catches Ctrl+C for being able to manually interrupt capture
-            while not overrun:
-                for p in self._pins:
-                    pkgs = await LAArbeiter.read_chunk(iface.read)
-                    if len(pkgs) == 0:
-                        zero_chunks += 1
-                    chunks += 1
-                    pins[p].extend(pkgs)
-                    if len(pkgs) > 255 - len(self._pins):
-                        overrun = True
-                        print("overrun")
+        # Step 1: record a buffer
+        # we do this before to get the full USB performance and not have any lag-spikes in between
+        try:
+            print(f"starting capture of {args.buffer_size} MB")
+            buffer = await iface.read(1024*1024 * args.buffer_size)
+        except KeyboardInterrupt:
+            pass
         finally:
-            events = []
-            cycles = 0
-            for p, pkgs in pins.items():
-                cycle = 0
-                for pkg in pkgs:
-                    for value, duration in SignalCompressor.decode_pkg(pkg):
-                        timestamp = cycle * 1_000_000_000 // self._sample_freq
-                        events.append((timestamp, p, value))
-                        cycle += duration
-                cycles = max(cycle, cycles)
-            events.sort(key=lambda e: e[0])
-
-            total_pkgs = sum(len(pkgs) for pkgs in pins.values())
-            total_bytes = chunks + total_pkgs * 2
-
-            print(f"captured {cycles} cycles")
-            print(f"chunking overhead: {chunks / total_bytes * 100}%")
-            print(f"zero chunks overhead: {zero_chunks / total_bytes * 100}%")
-            print(f"compression gain: {100 - (total_bytes * 8 / cycle * 100)}%")
-            
-
-            vcd_writer = VCDWriter(args.file, timescale="1 ns", check_values=False)
-            vcd_signals = {
-                p: vcd_writer.register_var(scope="", name="pin[{}]".format(p), var_type="wire", 
-                                           size=1, init=0)
-                for p in pins.keys()
-            }
-            for timestamp, p, value in events:
-                signal = vcd_signals[p]
-                vcd_writer.change(signal, timestamp, value)
-            vcd_writer.close(timestamp)
+            print("captured buffer, converting...")
+        
+
+        # Step 2: parse the packets from the captured buffer and sort them into channels
+        ptr = 0
+        async def read(size, ) -> bytes:
+            nonlocal ptr
+            to_return = buffer[ptr:ptr+size]
+            ptr += size
+            if ptr >= len(buffer):
+                return None
+            return to_return
+        channels = defaultdict(list)
+        chunks = 0
+        while True:
+            read_result = await LAarbiter.read_chunk(read)
+            if read_result is None:
+                break
+            channel, chunk = read_result
+            if len(chunk) == 255:
+                print(f"channel {channel} overrun")
+                break
+            channels[self._pins[channel]].extend(chunk)
+            chunks += 1
+
+        # Step 3: convert each channels packets into events, attach timestamps and sort them by
+        # timestamp
+        events = []
+        cycles = None
+        for p, pkgs in channels.items():
+            cycle = 0
+            for pkg in pkgs:
+                for value, duration in SignalCompressor.decode_pkg(pkg):
+                    events.append((cycle, p, value))
+                    cycle += duration
+            cycles = cycle if cycles is None else cycle if cycle < cycles else cycles
+        events.sort(key=lambda e: e[0])
+
+        # Step 3.5: report statistics
+        total_pkgs = sum(len(pkgs) for pkgs in channels.values())
+        total_bytes = chunks + total_pkgs * 2
+        print(f"captured {cycles} samples ({cycles / self._sample_freq * 1000}ms)")
+        print(f"chunking overhead: {chunks / total_bytes * 100}%")
+        print(f"compression gain: {100 - (total_bytes * 8 / (cycle * len(self._pins)) * 100)}%")
+        
+
+        # Step 4: write out VCD file
+        vcd_writer = VCDWriter(args.file, timescale="1 ns", check_values=False)
+        vcd_signals = {
+            p: vcd_writer.register_var(scope="", name="pin[{}]".format(p), var_type="wire", 
+                                        size=1, init=0)
+            for p in self._pins
+        }
+        for cycle, p, value in events:
+            if cycle > cycles:
+                # we dont write any timestamps for which we dont have data on all channels
+                break
+            signal = vcd_signals[p]
+            timestamp = cycle * 1_000_000_000 // self._sample_freq
+            vcd_writer.change(signal, timestamp, value)
+        vcd_writer.close(timestamp)