Roflin/rebbarb
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

analyse-pcap: count UDP, because ROM streaming is UDP/FSP not TCP

Browse Source 
The 850 KB/s dump measurement does not bound ROM streaming, and the tool could
not have measured streaming at all: it only counted TCP payload, so a
streaming capture would have reported ~zero throughput.

Swiss's ROM streaming runs in the game via the patch driver's own stack
(cube/patches/bba/tcpip.c), which contains no TCP whatsoever -- UDP + FSP,
plus ICMP and ARP.  Reads are sized to the path MTU rather than 1024:

  _fsp.data_length = MIN(length, env->pmtu - (fsp->data - eth->data));

so ~1446 B of payload per datagram at a 1500 MTU, with QUEUE_SIZE 2
outstanding and udp->checksum = 0x0000 (no payload checksum).  None of the
menu path's TCP window, lwIP overhead or 1024-byte writes apply.

The analyser now counts UDP payload and picks the bulk direction by which way
the payload actually flows -- streaming is PC -> GC, the opposite of a disc
dump -- with --bulk to_gc to steer the gap analysis.  Self-test H replays the
streaming shape (1446 B datagrams, 2 per request) and checks the bulk
direction is identified and the payload counted.

Recorded in the TODO that "can it stream?" is still OPEN, but open on the GC's
side: the dump established the adapter has headroom (zero retransmissions,
~17% W5100 bus utilisation, 26% of the EXI ceiling).  The hard ceiling is
3375 KB/s and the GC's disc delivers ~2000-3100 KB/s, so full disc rate has no
margin -- but games read in bursts, not continuously at peak.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Dennis Brentjes
2026-10-10 15:32:45 +02:00
parent d8ddea13ba
commit 4e7a2ef429
3 changed files with 103 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files
scripts/test-analyse-pcap.py
+33
View File
@@ -158,6 +158,39 @@ else:
print("G 1024B segments + 2920B window -> window x RTT bound,")
print(" full-MSS suggested, coalescing warned against")
def udp_frame(src, dst, smac, dmac, payload):
udp = struct.pack("!HHHH", 7717, 7717, 8 + len(payload), 0) + payload
ip = struct.pack("!BBHHHBBH4s4s", 0x45, 0, 20 + len(udp), 0, 0, 64,
socket.IPPROTO_UDP, 0, src, dst)
return dmac + smac + b"\x08\x00" + ip + udp
# Scenario H: ROM streaming shape -- UDP/FSP, bulk flowing PC -> GC, with
# small requests going the other way. Before UDP was counted this reported
# zero throughput, because Swiss's in-game stack has no TCP at all.
pkts, t = [], 7000.0
for i in range(300):
pkts.append((t, udp_frame(GC, PC, MAC_GC, MAC_PC, b"\0" * 20))) # request
t += 0.0001
for _ in range(2): # 2 queued
pkts.append((t, udp_frame(PC, GC, MAC_PC, MAC_GC, b"\0" * 1446)))
t += 0.0002
t += 0.0008
pH = os.path.join(tmp, "h.pcap")
write_pcap(pH, pkts)
out = run(pH, "--bulk", "to_gc")
if "bulk direction: PC -> GC" not in out:
fails.append(f"H: bulk direction not detected as PC->GC\n{out}")
elif "UDP" not in out:
fails.append(f"H: UDP frames not counted\n{out}")
else:
# 600 x 1446 B over ~0.39 s should be well above 1 MB/s
kbs = float(out.split("throughput")[2].split("KB/s")[0].strip())
if kbs < 500:
fails.append(f"H: UDP payload undercounted, {kbs} KB/s")
else:
print(f"H UDP/FSP streaming shape -> bulk PC->GC, {kbs:.0f} KB/s")
print("\nFAILURES:\n " + "\n ".join(fails) if fails else
"\nAll analyse-pcap self-tests passed.")
sys.exit(1 if fails else 0)