31 lines
2.5 KiB
Markdown
31 lines
2.5 KiB
Markdown
# B23 — faster battery charging: LBC fast-charge current 450 → 720 mA (2026-10-07) — **PASS, persistent**
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## Change
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One device-tree property only: `&pm8916_charger { qcom,fast-charge-safe-current = <720000>; }`
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(`linux/dts/msm8916-jz08-aurora-b23.dts`, includes the B18 DTB). The pm8916_lbc supervisor (v4, B10B-5) programs
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IBAT_SAFE and IBAT_MAX from it: code = current / 90 mA − 1 → **0x04 (450 mA) → 0x07 (720 mA)**. The simple-battery node
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has no constant-charge-current property, so the safe current is also the charge current. Kernel (7.2.7-aurora-b18),
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initramfs (B12Q) and cmdline are unchanged; the DTB differs from B18 only in this property and the model string.
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Why not more: the LBC is a linear charger — PMIC dissipation is (VBUS − VBAT) · I; it has no input current limit,
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so a weak source sags below VIN_MIN (4.308 V) instead of limiting. 720 mA was the first step (hardware max 1440 mA).
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## RAM test (ram2, `b23/b23-boot.sh`, observer `b23/b23-mon.sh` every 30 s; nothing flashed)
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- Probe: `IBAT_MAX 07`, supervisor INIT → CHARGING, CHG_STATUS 05 (CC), FAST_CHG_ON + USB path 02, VDD_MAX 08 (4.20 V).
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- Source = laptop USB port: USB meter **0.724 A**; USBIN 4.67–4.78 V, no sag.
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- CC held for 55+ min without restart/latch/FAULT (VADC VBAT under charge 3.98 → 4.10 V).
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- PMIC temperature: max **55.7 °C** in the first 5 min, then 43–47 °C (part of the drop is the known ~7 °C
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backlight-off artefact of the PMIC sensor). Alert threshold 60 °C never reached.
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- CV (CHG_STATUS 03) from VADC ≈ 4.10 V; current then tapers (0.4 A on the meter) — normal, current does not speed up CV.
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## Persistent
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- Cache candidate `b23/cache/mkfs-cache-b23.sh` (B18 recipe, DTB b23) **01bfe522**; lk2nd extlinux emulator
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(`b23/cache/emu/run-emu-b23.sh`): B18 regression identical, B23 boots label `b23` with DTB 89eade0f, fault variants revert.
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- Written by `b23/B23-write.sh` (HW EDL): **B23_CACHE_WRITE_VERIFIED** — readback == image, all other partitions unchanged,
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pre-write cache readback == B18 ac82811a kept. Rollback: `b23/B23-rollback.sh` → B18 `ac82811a`.
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- Cold boot from eMMC (full power-off, no RESET): model "JZ08AU Aurora (B23 charge 720 mA)", `IBAT_MAX 07`, CHARGING.
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## Effect / limits
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CC phase (empty → ≈ 4.1 V) ≈ 1.6× faster; the CV tail is unchanged. Board load (CPU, backlight) comes out of the same
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input current (no power path). Worst case (long CC from ≈ 3.7 V with CPU load) not yet measured thermally; still no
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thermal derating in the supervisor.
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