Error: not keeping up with rtl_tcp

[domasofan]

Hi all,

I just got the latest rtlamr and rtl_tcp versions.
Running under Windows 11 Version 25H2 (Build 26200.8246).
rtl_tcp version daily build from 19 April 2026, Windows, 64 Bit.
rtlamr v0.9.5 from 25 April 2026, Windows, 64 Bit.

Here is the output from rtl_tcp and rtlamr:

rtl_tcp:

$ rtl_tcp

Found 1 device(s):
  0:  Generic, RTL2832U, SN: 77771111153705700

Using device 0: Generic RTL2832U
Found Rafael Micro R820T tuner
[R82XX] PLL not locked!
Tuned to 100000000 Hz.
listening...
Use the device argument 'rtl_tcp=127.0.0.1:1234' in OsmoSDR (gr-osmosdr) source
to receive samples in GRC and control rtl_tcp parameters (frequency, gain, ...).
client accepted! SimonPC2024 49402
set freq 912600155
set sample rate 2359296
set gain mode 0

rtlamr:

$ rtlamr

C:\Users\bemasher\Desktop\Go\src\github.com\bemasher\
time=2026-04-26T01:00:29.878+02:00 level=INFO source=rtlamr\protocol\decode.go:45 msg="CenterFreq: 912600155"
time=2026-04-26T01:00:29.901+02:00 level=INFO source=rtlamr\protocol\decode.go:46 msg="SampleRate: 2359296"
time=2026-04-26T01:00:29.901+02:00 level=INFO source=rtlamr\protocol\decode.go:47 msg="DataRate: 32768"
time=2026-04-26T01:00:29.901+02:00 level=INFO source=rtlamr\protocol\decode.go:48 msg="ChipLength: 72"
time=2026-04-26T01:00:29.901+02:00 level=INFO source=rtlamr\protocol\decode.go:49 msg="PreambleSymbols: 21"
time=2026-04-26T01:00:29.901+02:00 level=INFO source=rtlamr\protocol\decode.go:50 msg="PreambleLength: 3024"
time=2026-04-26T01:00:29.901+02:00 level=INFO source=rtlamr\protocol\decode.go:51 msg="PacketSymbols: 96"
time=2026-04-26T01:00:29.901+02:00 level=INFO source=rtlamr\protocol\decode.go:52 msg="PacketLength: 13824"
time=2026-04-26T01:00:29.901+02:00 level=INFO source=rtlamr\protocol\decode.go:59 msg="Protocols: scm"
time=2026-04-26T01:00:29.901+02:00 level=INFO source=rtlamr\protocol\decode.go:60 msg="Preambles: 111110010101001100000"
time=2026-04-26T01:00:29.902+02:00 level=INFO source=rtlamr\main.go:129 msg=rtl_tcp GainCount=29
time=2026-04-26T01:00:30.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2240512
time=2026-04-26T01:00:32.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2236416
time=2026-04-26T01:00:36.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2355200
time=2026-04-26T01:00:37.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2355200
time=2026-04-26T01:00:40.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2269184
time=2026-04-26T01:00:41.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2334720
time=2026-04-26T01:00:44.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2252800
time=2026-04-26T01:00:46.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2347008
time=2026-04-26T01:00:51.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2306048
time=2026-04-26T01:00:55.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2314240
time=2026-04-26T01:00:56.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2342912
time=2026-04-26T01:00:59.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2334720
time=2026-04-26T01:01:03.922+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2322432
time=2026-04-26T01:01:05.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2347008
time=2026-04-26T01:01:07.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2347008
time=2026-04-26T01:01:09.917+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2322432
time=2026-04-26T01:01:11.902+02:00 level=ERROR source=rtlamr\main.go:194 msg="not keeping up with rtl_tcp" rate=2351104

I am not sure if this is a bug or just a setting that is not right.
Maybe someone could tell me what is going on here?

Greetings and thanks,
Simon

[afernandez2000]

With the default -symbollength=72, the decoder asks rtl_tcp for SampleRate = DataRate * ChipLength = 32768 * 72 = 2,359,296 samples/s (protocol/decode.go:132-133). You're getting 2,232,320 — about 5.4% short. The RTL2832 only supports a discrete set of sample rates and tends to top out around 2.4 MS/s sustained over USB; 2.359296 MS/s is right at the edge and many dongles silently deliver less, especially on USB 2.0 or under CPU pressure.

[bemasher]

Probably it is not reasonable to expect to receive an exact number of bytes every second, but instead some threshold like 95% of the bytes, and warn the user below that.

rtlamr/main.go

Lines 193 to 195 in a1f6df8

	if bytesRead>>1 < rcvr.d.Cfg.SampleRate {
	slog.Error("not keeping up with rtl_tcp", "rate", bytesRead>>1)
	}

The intent is to warn users when samples are not being consumed fast enough and causing rtl_tcp to buffer unconsumed blocks in its linked list, because this is a common "what's wrong?" issue.

[AStoker]

I'm running this on my Mac, and I'm having the same issue. I have the SDR plugged into a USB 3 port, so the data rate should be fine from that. Are you saying the RTL-SDR (in my case the RTL-SDR Blog V4) isn't capable of keeping up? I know it was running correctly with linux when I last tried last year.

~ % rtl_tcp
Found 1 device(s):
  0:  RTLSDRBlog, Blog V4, SN: 00000001

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R828D tuner
RTL-SDR Blog V4 Detected
Tuned to 100000000 Hz.
listening...
Use the device argument 'rtl_tcp=127.0.0.1:1234' in OsmoSDR (gr-osmosdr) source
to receive samples in GRC and control rtl_tcp parameters (frequency, gain, ...).
client accepted! localhost 54694
set freq 912600155
set sample rate 2359296
set gain mode 0

~ % rtlamr
/Users/andrew/go/pkg/mod/github.com/bemasher/
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/protocol/decode.go:45 msg="CenterFreq: 912600155"
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/protocol/decode.go:46 msg="SampleRate: 2359296"
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/protocol/decode.go:47 msg="DataRate: 32768"
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/protocol/decode.go:48 msg="ChipLength: 72"
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/protocol/decode.go:49 msg="PreambleSymbols: 21"
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/protocol/decode.go:50 msg="PreambleLength: 3024"
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/protocol/decode.go:51 msg="PacketSymbols: 96"
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/protocol/decode.go:52 msg="PacketLength: 13824"
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/protocol/decode.go:59 msg="Protocols: scm"
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/protocol/decode.go:60 msg="Preambles: 111110010101001100000"
time=2026-05-04T16:14:30.317-04:00 level=INFO source=rtlamr@v0.9.5/main.go:129 msg=rtl_tcp GainCount=29
time=2026-05-04T16:14:31.337-04:00 level=ERROR source=rtlamr@v0.9.5/main.go:194 msg="not keeping up with rtl_tcp" rate=2232320