Add RAM-buffered queue (BufferedQueue, RamRing, SharedRamRing)#123
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Introduces queue::buffer with: - RamRing<N>: fixed-capacity ring buffer for variable-length items - OverflowPolicy: Err or DiscardOldest on full ring - BufferedQueue<S,C,N>: accepts sync enqueues into RAM, drains to flash async - SharedRamRing<N>: ISR-safe variant using embassy-sync (optional embassy feature) FIFO ordering is preserved across the RAM→flash boundary. Power-fail note: items still in RAM at power loss are discarded; drained items carry the usual sequential-storage guarantees.
diondokter
reviewed
Mar 19, 2026
SharedRamRing no longer depends on embassy-sync. The blocking mutex is replaced with critical_section::Mutex (borrow pattern), and the Signal is replaced with a minimal WakeSignal built from an AtomicBool and a stored core::task::Waker — no runtime dependency required. The feature flag is renamed from `embassy` to `critical-section` to reflect the actual dependency.
…Signal" This reverts commit a7b0efb.
Member
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Oh we've got new clippy lints and it's rightfully pointing out I've been lazy 🙈 I'll improve that when the next breaking change comes around I guess |
- Rename feature `embassy` to `shared-ram-ring` per maintainer request
- Run cargo fmt (import order, line-length wrapping)
- Add #[allow(clippy::result_unit_err)] to push/push_overwriting/enqueue
- Fix include!("mock_flash.rs") → include!("../mock_flash.rs") in doctest
(path is now relative to src/queue/mod.rs, not src/queue.rs)
Contributor
Author
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Let me know if there's anything else I need to address. Happy to hopefully contribute to your awesome work! |
diondokter
reviewed
Mar 19, 2026
… oldest_ram_item_len - pop/peek now read flash first (flash items are always older) and fall back to the oldest RAM item if flash is empty, avoiding unnecessary drain-all-to-flash on every read; allow_overwrite removed from both since they no longer write to flash - Remove pub storage() accessor — it allowed callers to bypass ordering invariants (footgunny per reviewer) - Remove oldest_ram_item_len() — not practically useful in no_std without alloc; callers can size scratch buffers statically - Restructure pop_reads_flash_before_ram test to use QueueStorage directly instead of the removed storage() accessor
Contributor
Author
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OK I think I addressed your comments @diondokter. Let me know if there's anything else pending. |
Member
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Thanks! |
Member
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Released as v7.2.0 |
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Summary
This adds a RAM-buffered wrapper around
QueueStoragefor cases where the producer is faster than NOR flash can keep up with.RamRing<N>— compact fixed-capacity ring buffer for variable-length byte items (2-byte LE length prefix per item)OverflowPolicy—ErrorDiscardOldestwhen the ring is fullBufferedQueue<S, C, N>— wrapsQueueStoragewith a RAM ring;enqueueis synchronous and never touches flash,drain_one/drain_allcommit items to flash asynchronouslySharedRamRing<N>— ISR-safe variant behind the optionalembassyfeature; wraps the ring in aCriticalSectionRawMutexand uses an EmbassySignalto wake a drain taskFIFO ordering is preserved across the RAM→flash boundary:
pop/peekdrain any pending RAM items to flash first, then read from flash.Power-fail note: items still in the RAM ring at power loss are discarded; items that have been drained carry the usual sequential-storage guarantees.
Dependency note
SharedRamRingpulls inembassy-sync(gated behind theembassyfeature). Theembassy-synctypes are not part of the public API — the only public surface isSharedRamRing<N>itself. Happy to revisit the dependency (e.g. swap the mutex for directcritical_section::withcalls and hand-roll a minimal signal) if you'd prefer to avoid it.