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Drop the untested data-length suggestion from the MTU advice - #34

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docs/drop-untested-dle-tip
Nov 13, 2026
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ps2 merged 1 commit into
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docs/drop-untested-dle-tip

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@ps2 ps2 commented Nov 13, 2026

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The MTU troubleshooting section, and the error the simulator prints when the link is too
small, both suggested:

sudo hcitool -i hci0 cmd 0x08 0x0024 fb 00 48 03   # LE Write Suggested Default Data Length

That was written for a 4.2+ radio that still negotiates an ATT MTU of 185. Nobody has
reported that case. The one Pi 4 that reported a radio older than its board turned out to
be missing BCM4345C0.hcd; installing the firmware moved it from 4.1/Broadcom to
5.0/Cypress and the pairing went through. The command itself was never run against a
failing pairing, so we don't know that it changes a negotiated MTU.

A runtime error is the wrong place for a guess, so this removes it from both places. The
error now points at the firmware note in the README, which is what actually fixed the one
real case, and the dongle and -transport impossible remain as the advice that has
worked.

go build ./..., go vet ./pkg/bluetooth/ and go test ./... are green (all packages
pass, unchanged from main).

LE Write Suggested Default Data Length was offered for a 4.2+ radio that
still negotiates an ATT MTU of 185, which nobody has run into. The one Pi 4
that reported a radio older than its board was missing BCM4345C0.hcd, and
installing the firmware is what fixed it.

Point the runtime error at the firmware note instead, and leave the dongle
and -transport impossible as the advice that has actually worked.
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ps2 marked this pull request as ready for review November 13, 2026 15:08
@ps2
ps2 merged commit 2568438 into main Nov 13, 2026
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