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Bosminer panics on low-difficulty chains: what eCash fork-day operators need to know

· solofork · pre-launch testing

TL;DR. BraiinsOS's bosminer firmware crashes via a Rust panic on any chain where the pool's share difficulty exceeds the network difficulty. True on Bitcoin mainnet (where it never fires), false on signet, regtest, custom signets, and — relevant to the planned August 2026 eCash hard fork — the first ~2,016 blocks of eCash mainnet at minimum difficulty. ASIC operators planning to mine the bonanza window should not run BraiinsOS until this is patched.

The setup

While bringing up an independent solo mining pool for the LayerTwoLabs eCash fork, we wired a 1 TH/s S19-class miner running BraiinsOS into our public stratum endpoint on the L2L signet testnet (network difficulty roughly 0.001).

The miner connected, completed mining.configure with version-rolling negotiation, subscribed, received a difficulty assignment, authorised, and got its first mining.notify work message — and then closed the TCP connection cleanly (RDHUP) about fifteen seconds later, without ever sending a mining.submit. Reconnect, repeat, every forty seconds. No protocol-level error from the client; just silent disconnect.

Finding the panic

From the pool side, this looks like a classic "miner doesn't like our work." From logread -e bosminer on the miner itself, it's much more specific:

thread 'tokio-runtime-worker' panicked at open/bosminer/bosminer/src/job.rs:202:13:
assertion failed: &solution.network_target() <= job_target
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Twenty-eight identical panics in one log capture. The assertion is unconditional — every solution the ASIC produces triggers the check, and on a low-diff network every solution fails it.

Why the assertion fails on signet

The assertion enforces network_target ≤ job_target, equivalently share_difficulty ≤ network_difficulty. The implicit assumption: the network is always at least as hard to satisfy as the share difficulty the pool is asking for.

This holds on Bitcoin mainnet by orders of magnitude — network diff is roughly 80 trillion, share diff is typically thousands to millions, so the assertion never gets close to firing. It fails immediately on:

It's the last bullet that matters for production planning.

Implication: the bonanza window is exactly when this bites

The eCash fork's design includes a one-time difficulty reset to the minimum value at fork height (Bitcoin block 964,000, planned for August 2026). For roughly the first 2,016 blocks the network difficulty is below what any sane share difficulty would be — a window where mining is unusually profitable per unit of hashrate, and exactly where pool operators expect to attract opportunistic ASIC capacity.

Any miner pointing a BraiinsOS-firmware ASIC at any pool during that window will hit this assertion on the first solution and crash-loop. Pool operators won't see a stratum-level error; they'll see authenticated workers that connect and disconnect every minute, never submitting shares.

What our pool got right (verified via tcpdump)

Capture of the actual stratum bytes between the miner and our pool ruled out a lot of plausible alternative causes. The pool sent valid mining.configure (negotiating version-rolling with mask 1fffe000), mining.subscribe with proper extranonce assignment, mining.set_difficulty, mining.notify with all the required fields (job ID, prevhash, coinbase parts, version, nbits, ntime), and mining.authorize result. Nothing in the wire traffic is malformed.

What's not the bug, despite being suspect-looking from outside:

Resolution paths

1. Patch bosminer (right place for the fix)

The assertion is debug-grade — it should be a debug_assert! or removed entirely in release builds. One-line change at bosminer/src/job.rs:202. If a Braiins maintainer is reading this: a point release before fork day would solve the problem at the source for the entire ASIC fleet. We're reaching out via public channels and will update this post once a fix is in flight.

2. Use non-bosminer firmware

cgminer, vnish, and stock Antminer firmware don't carry this assertion. ASIC operators planning to mine the bonanza window can switch firmware temporarily and roll back to BraiinsOS once network difficulty climbs into the safe regime.

3. Pool-side workaround (CKpool fractional difficulty)

From the pool operator's side, we can serve fractional share difficulty below the network difficulty so the assertion holds. CKpool's current configuration parser stores mindiff and startdiff as int64; the fix is to convert them and the related vardiff variables to double throughout. This is roughly an eighty-line patch across ckpool.h, ckpool.c, and stratifier.c. We're holding it as a defensive backstop in case BraiinsOS doesn't ship a fix in time.

Wider context

This is a class of bug that's been latent because Bitcoin mainnet's difficulty has been so high for so long that nobody hits it. The eCash fork's planned difficulty-reset-to-minimum is one of the rare scenarios that exposes it. Worth flagging to the broader Bitcoin mining-firmware community: any chain with a fresh-start or low-diff regime — testnets, signets, regtest, alternative networks, or future hard forks — is going to surface this.

What we're doing about it

We're an independent solo mining pool for the eCash fork, in pre-launch testing on L2L's signet with mainnet readiness for fork day. Our stratum endpoint is verified end-to-end with reference miners; the bosminer issue is firmware-side, not pool-side.

If you operate ASIC capacity and plan to mine the eCash fork: take note of the firmware constraint above. We'll publish updated guidance as the situation evolves.

Pool URL and connection details: solofork.com. Architecture and live API: api.solofork.com/pool/pool.status.