docs(hardware): add savearth PCB BOMs, netlists, knowledge base

- v2.5, v2.6, v2.7, v2.8, v2.9 parsed BOMs and netlists
- v2.8/v2.9 knowledge base (component data, supply chain)
- v2.8 README with pinout documentation
- v2.9 EasyEDA project file
- Hardware all-versions knowledge base

hardware/v2.8/README.md

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+# PCB v2.8 Hardware Reference
+
+**Last updated:** 2026-07-15
+**Source:** EasyEDA Pro project `Savearth GBT.eprj` + firmware `bsp_v28.c`
+
+---
+
+## Component Map
+
+### Active ICs
+
+| Ref | Symbol | Part | Function |
+|-----|--------|------|----------|
+| U3 | ESP32-S3-WROOM-1-N8R8 | ESPRESSIF | Main MCU, 8MB flash, 8MB PSRAM |
+| U11 | BQ25895RTWR | TI | Battery charger/monitor, I2C 0x6A |
+| U12 | PCAL9538ABSHP | NXP | 8-bit I/O expander, I2C 0x70 |
+| U9 | MIC94073YMT-TR | MICROCHIP | P-channel load switch (PWR_EN → SW_3.3V) |
+| U2 | AP2112K-3.3TRG1 | DIODES | 3.3V LDO regulator (ESP32 always-on rail) |
+| U5 | ICS-43434 | TDK InvenSense | MEMS microphone, I2S |
+| U14 | DW01 | SHIKUES | Battery protection IC |
+
+### Discrete Semiconductors
+
+| Ref | Symbol | Part | Function |
+|-----|--------|------|----------|
+| Q2 | Si2302CDS-T1-E3-HXY | HXY | N-MOSFET (load switch) |
+| Q4 | AO3400A | YTL | N-MOSFET |
+| Q5 | AO3400A | YTL | N-MOSFET |
+| D1 | LESD5D5.0CT1G | KUU | TVS/ESD protection |
+| D2 | LESD5D5.0CT1G | KUU | TVS/ESD protection |
+| D3 | LESD5D5.0CT1G | KUU | TVS/ESD protection |
+| D5 | BAT760-7 | DIODES | Schottky diode |
+| D6 | BAT760-7 | DIODES | Schottky diode |
+| D7 | BAS16HT1G | onsemi | Switching diode |
+| D9 | VSKY10201406-G4-08 | VISHAY | Schottky diode |
+| D10 | V8PAN50-M3/I | VISHAY | Schottky diode |
+
+### Passives (selected)
+
+| Ref | Symbol | Value | Function |
+|-----|--------|-------|----------|
+| R23 | 0402WGF1002TCE | 10kΩ | GPIO0 pull-up to 3.3V |
+| R19 | 0402WGF100JTCE | 10Ω | Series resistor |
+| R26 | 0402WGF220JTCE | 22Ω | Series resistor |
+| R27 | 0402WGF220JTCE | 22Ω | Series resistor |
+| R28 | 1206W4F1004T5E | 1MΩ | High-value resistor |
+| R37 | CRCW04020000Z0ED | 0Ω | Jumper |
+| R43 | CRCW04025K23FKED | 5.23kΩ | Precision resistor |
+| R44 | CRCW040230K1FKED | 30.1kΩ | Precision resistor |
+| R45 | CRCW040210K0FKED | 10kΩ | Resistor |
+| R46 | CL0402FN33RP | 33Ω | Series resistor |
+| R50 | HOT1206-2W-0R | 0Ω | Jumper (high current) |
+| C17 | 1206B103K202NT | 10nF 2kV | High-voltage cap (USB protection) |
+| L3 | IHLP2020BZER2R2M11 | 2.2µH | Power inductor |
+
+### Connectors
+
+| Ref | Symbol | Part | Function |
+|-----|--------|------|----------|
+| USB1 | HYCW396-USBC16-712B | USB-C | USB Type-C connector |
+| CN1 | HC-FPC-0.5-40P-FH20 | FPC 40-pin | LCD ribbon connector |
+| CON_BAT | S3B-PH-SM4-TB | JST PH 2-pin | Battery connector |
+| FlashPort | HX PZ1.27-1x6P | Pin header 6-pin | Debug/flash header |
+| RS1 | 59170-1-S-00-D | Littelfuse | Reed switch (magnet sensor) |
+| SW2 | SS12D00G3 | Slide switch | Power switch |
+| PIR1 | AMD312 | PIR sensor | Motion detection |
+| NTC | 103AT-2 | NTC thermistor | Temperature sensing |
+
+### FlashPort Pinout (6-pin debug header)
+
+| Pin | Net | Connection | Notes |
+|-----|-----|------------|-------|
+| 1 | +3.3V | Power rail | 3.3V supply |
+| 2 | EN | U3 pin 3 (EN) | Chip enable (active high) |
+| 3 | TX0_AP_BTN | U3 pin 37 (TXD0) | UART0 TX |
+| 4 | RX0_EN_REG3.3 | U3 pin 36 (RXD0) | **ERRATA: The problematic wire** |
+| 5 | IO0_LCD_RST | U3 pin 27 (IO0) | GPIO0 boot strap |
+| 6 | GND | Ground | Reference |
+
+> **Warning:** Pin 4 (RX0_EN_REG3.3) was the net that created the v2.8 root cause.
+> On affected boards, this pin had a physical wire to VSYS that injected noise.
+
+---
+
+## Power Rail Topology
+
+```
+VBUS (USB 5V)
+    │
+    ├──→ D10 (V8PAN50) ──→ USB protection
+    ├──→ C17 (10nF 2kV) ──→ EMI filter
+    │
+    ▼
+┌─────────────────────────────────────────────┐
+│  U11: BQ25895RTWR (I2C 0x6A)              │
+│  IN+ = VBUS                                │
+│  BAT = Li-Ion cell (via CON_BAT)           │
+│  SYS = VSYS (switched output)              │
+│  PMID = VBUS decoupling                    │
+│  REGN = internal LDO (charge pump)         │
+│  SW = switching node (inductor L3)         │
+└──────┬──────────────────┬───────────────────┘
+       │ VSYS             │ VBAT
+       │                  ▼
+       │            ┌──────────┐
+       │            │ Battery  │
+       │            │ Li-Ion   │
+       │            └──────────┘
+       │
+       ▼
+┌──────────────────────────────────┐
+│  U9: MIC94073 (load switch)     │
+│  IN  = VSYS                     │
+│  EN  = PWR_EN (GPIO1)          │
+│  OUT = SW_3.3V                  │
+└──────────┬───────────────────────┘
+           │ SW_3.3V
+           ▼
+    ┌──────┴──────┐
+    │             │
+    ▼             ▼
+┌────────┐  ┌────────────────┐
+│ST7701S │  │  PCAL9538A     │
+│ (LCD)  │  │  IO Expander   │
+└────────┘  └────────────────┘
+
+U2: AP2112K-3.3 ──→ 3.3V always-on rail (ESP32-S3 VDD)
+    IN = VSYS (always powered)
+    OUT = 3.3V (ESP32 core, I2C, flash)
+```
+
+### Rail Summary
+
+| Rail | Source | Voltage | Loads | Control |
+|------|--------|---------|-------|---------|
+| VBUS | USB-C | 5V | BQ25895 input | USB connector |
+| VBAT | Li-Ion | 3.0-4.2V | BQ25895 battery port | Charge/discharge |
+| VSYS | BQ25895 | 3.0-4.5V | System supply | BQ25895 internal |
+| SW_3.3V | MIC94073 | 3.3V | LCD, IO expander, PIR | GPIO1 (PWR_EN) |
+| 3.3V | AP2112K | 3.3V | ESP32-S3, I2C, flash | Always on |
+
+---
+
+## GPIO Pin Map (from firmware)
+
+### Direct GPIO Connections
+
+| GPIO | Function | Net | Component |
+|------|----------|-----|-----------|
+| 0 | LCD_RST / Boot strap | IO0_LCD_RST | ST7701S reset |
+| 1 | PWR_EN | PWR_EN | MIC94073 enable |
+| 2 | I2S_MIC_LRCL | WS | Microphone |
+| 3 | LCD_R2 | R2 | ST7701S RGB |
+| 4 | LCD_PCLK | LCD_PCLK | ST7701S clock |
+| 5 | LCD_B1 | B1 | ST7701S RGB |
+| 6 | LCD_BACKLIGHT | BL_PWM | ST7701S backlight |
+| 7 | LCD_SPI_SCL | LCD_SCK | ST7701S SPI |
+| 8 | IOEXP_A0 | A0 | PCAL9538A address |
+| 9 | LCD_G5 | G5 | ST7701S RGB |
+| 10 | I2C0_SDA | SDA | I2C bus |
+| 11 | I2C0_SCL | SCL | I2C bus |
+| 12 | LCD_G2 | G2 | ST7701S RGB |
+| 13 | LCD_G1 | G1 | ST7701S RGB |
+| 14 | PIR | AM312 | PIR sensor |
+| 15 | LCD_SPI_SDA | LCD_SDA | ST7701S SPI |
+| 16 | LCD_SPI_CS | LCD_CS | ST7701S SPI |
+| 17 | IOEXP_RESET | RST | PCAL9538A reset |
+| 18 | IOEXP_A1 | A1 | PCAL9538A address |
+| 21 | LCD_B5 | B5 | ST7701S RGB |
+| 38 | LCD_HSYNC | LCD_HSYNC | ST7701S sync |
+| 39 | LCD_VSYNC | LCD_VSYNC | ST7701S sync |
+| 40 | LCD_DE | LCD_DE | ST7701S enable |
+| 41 | I2S_MIC_DOUT | DOUT | Microphone |
+| 42 | I2S_MIC_BCLK | BSCK | Microphone |
+| 45 | LCD_B2 | B2 | ST7701S RGB |
+| 46 | LCD_R1 | R1 | ST7701S RGB |
+| 47 | LCD_B4 | B4 | ST7701S RGB |
+| 48 | LCD_B3 | B3 | ST7701S RGB |
+
+### PCAL9538A IO Expander (I2C 0x70)
+
+| Pin | Net | Function | Direction |
+|-----|-----|----------|-----------|
+| P0 | G4 | LCD RGB data (static) | Output |
+| P1 | G3 | LCD RGB data (static) | Output |
+| P2 | R5 | LCD RGB data (static) | Output |
+| P3 | R4 | LCD RGB data (static) | Output |
+| P4 | R3 | LCD RGB data (static) | Output |
+| P5 | PROG_EN | Reed switch (magnet) | Input |
+| P6 | NC | Not connected | — |
+| P7 | NC | Not connected | — |
+
+---
+
+## Known Hardware Issues (Errata)
+
+### ERRATA 1: RX0-VSYS Wire (ROOT CAUSE — CORRECTED)
+
+**Original diagnosis:** LCD ESD diode clamping GPIO0.
+**Actual root cause:** Physical wire between ESP32-S3 RX0 (GPIO44) and VSYS (BQ25895 SW output).
+
+- **Net name in schematic:** `RX0_EN_REG3.3`
+- **Components on this net (4 pins):**
+  - **U3 pin 36 (RXD0)** — ESP32-S3 UART0 RX
+  - **FlashPort pin 4** — Debug header UART RX
+  - **D6 pin 2** — BAT760-7 Schottky diode
+  - **R32 pin 2** — 10kΩ resistor to GND
+- **Effect:** Switching noise from BQ25895 buck converter couples into ESP32-S3 power domain, causing spurious resets into download mode
+- **Fix:** Remove the physical wire. Firmware mitigations (PWR_EN hold, GPIO0 pull-up) retained as belt-and-suspenders.
+
+### ERRATA 2: GPIO0 Boot Strap Trap
+
+**Net:** `IO0_LCD_RST`
+**Components on this net (4 pins):**
+- **U3 pin 27 (IO0)** — ESP32-S3 boot strap pin
+- **R23 pin 2** — 10kΩ pull-up to +3.3V
+- **CN1 pin 35** — LCD FPC connector (ST7701S reset)
+- **FlashPort pin 5** — Debug header GPIO0
+
+- GPIO0 is shared between ESP32-S3 boot strap and ST7701S LCD reset
+- R23 (10kΩ) pulls GPIO0 high for normal boot
+- When LCD is unpowered, ESD diode can clamp GPIO0 low (secondary issue)
+- **Mitigation:** PWR_EN asserted before ROM samples GPIO0; GPIO0 held high via RTC during sleep
+- **Status:** RETAINED as belt-and-suspenders; not the primary root cause
+
+### ERRATA 3: BQ25895 Watchdog
+
+- BQ25895 internal watchdog can fire, resetting charger registers to defaults
+- Firmware detects via REG_0C bit 7 and re-applies settings
+- **Mitigation:** Watchdog disabled in charger init
+
+### ERRATA 4: Weak VBUS Boot Throttle
+
+- At boot, if VBUS is weak (<4300mV or SDP/UNKNOWN/NONE), charger throttled to 300mA
+- Re-enabled when VBUS recovers (≥4400mV, stable)
+- **Status:** Good practice for USB-powered scenarios
+
+### ERRATA 5: LCD Noise (v2.8 specific)
+
+- 5 RGB data bits held static by IO expander causes visible dithering artifacts
+- **Mitigation:** NRCTRL noise reduction + SECTRL sharpness control enabled
+- **VOP override:** VRHS raised from 0x6D to 0x70 for better contrast
+
+---
+
+## Critical Net Names
+
+| Net | Connections | Notes |
+|-----|-------------|-------|
+| `RX0_EN_REG3.3` | GPIO44 ↔ VSYS path | **THE problematic wire** |
+| `PWR_EN` | GPIO1 → MIC94073 EN | Power enable for SW_3.3V |
+| `IO0_LCD_RST` | GPIO0 ↔ ST7701S RST | Boot strap + LCD reset |
+| `VSYS` | BQ25895 SYS → system | Main switched rail |
+| `VBUS` | USB-C → BQ25895 IN | USB 5V input |
+| `SW_3.3V` | MIC94073 OUT → LCD, IO expander | Switched peripheral rail |
+| `PROG_EN` | PCAL9538A P5 ↔ RS1 | Reed switch input |
+| `BAT` | BQ25895 BAT ↔ CON_BAT | Battery connection |
+| `PMID` | BQ25895 PMID decoupling | Input decoupling |
+| `REGN` | BQ25895 REGN decoupling | Charge pump LDO |
+| `SW` | BQ25895 SW ↔ L3 | Switching node |
+| `SDA` | GPIO10 ↔ U11/U12 | I2C data |
+| `SCL` | GPIO11 ↔ U11/U12 | I2C clock |
+| `A0` | GPIO8 → PCAL9538A | I2C address bit 0 |
+| `A1` | GPIO18 → PCAL9538A | I2C address bit 1 |
+| `RST` | GPIO17 → PCAL9538A | IO expander reset |
+| `EN` | PCAL9538A enable | — |
+| `USB_DP` | USB-C D+ | USB data |
+| `USB_DN` | USB-C D- | USB data |
+| `BL_PWM` | GPIO6 → ST7701S | Backlight control |
+| `TX0_AP_BTN` | — | Button/UART |