rebbarb/hardware/re-bba-rb/TODO.md

re-bba-rb board — open items from hardware review (2026-07-17)

Full review of schematics + PCB against component datasheets (datasheets/ — restore from commit db457a0, see Housekeeping), the WIZnet W5100S reference schematic, and JLCPCB manufacturing limits. ERC/DRC: clean.

Critical — must fix before (or with) next fab

• EXI DO/DI swapped at J3 (exi.kicad_sch). YAGCD SP1 naming is console-perspective: pin 6 DO = GC data out → adapter's MOSI input; pin 9 DI = GC data in ← adapter's MISO output. Board has J3.6 → EXI_MISO (FPGA output — bus contention with the GC driver) and J3.9 → EXI_MOSI. Verified via SD Gecko (MC pin 5 DO → SD CMD input) and SD2SP2 (DO → OR gate → SD CMD). - [ ] Fix the SP1 pin table in docs/gc_bba_fpga_design.md (§ SP1 pinout, "DO (MISO) Adapter → GC" is backwards — root cause). - [ ] Fix schematic labels (or PCB routing) so names match reality. - [ ] Decide: keep current copper and swap in synth.py pin constraints (both FPGA pins are plain IOBs: pin 3 = IOB_9b, pin 4 = IOB_8a), or re-route. Existing boards are rescuable in constraints alone.
• W5100S MDI termination network missing (ethernet.kicad_sch). Per WIZnet W5100S reference schematic: 49.9 Ω from each of TXOP/TXON/RXIP/RXIN to a common node with 0.1 µF to GND, placed near the chip ("to avoid the 100M overshoot"); optionally 3.3 Ω series damping in each line. Board routes the pairs straight through D4/D5 to the magjack. - [ ] Add 4× 49.9 Ω 1% + 2× 0.1 µF termination. - [ ] Place C51/C52 physically at J2 pins 4/5 (center taps). - [ ] Reconsider D4/D5 (USBLC6 on the line side of the magnetics): unusual — transformer already isolates; their VBUS pins float so they only clamp to GND. Remove or justify.
• FT2232H EEPROM interface (Usb Connector.kicad_sch): datasheet Table 3.4 requires EEDATA → 93LC46B DO via 2.2 kΩ plus 10 kΩ pull-up on DO to VCC (DI stays direct). Board ties DO and DI both directly to EE_DATA → read contention, unreliable EEPROM enumeration.

Functional / robustness

• iceprog pin mismatch: iceprog hardcodes CS=ADBUS4, CDONE=ADBUS6, CRESET=ADBUS7. Board uses FLASH_CS=ADBUS3, CDONE=ACBUS1, CRESET=ACBUS0. Rewire to the iCEbreaker convention, or maintain a patched iceprog.
• TPS2116 PR1 divider margin: 200k/100k gives PR1 = 1.10 V vs VREF = 1.0 V ±8 % (max 1.08 V) — 20 mV worst-case margin against the 3.3 V buck output. Change R3 to 150 k → switchover at 2.30–2.70 V.
• ETH_RST pull-up: W5100S RSTn is a plain input (no internal pull) and floats while the FPGA configures. Add 10 k to ETH_3V3 (not 3V3, so it sits low when the ETH rail is off).
• Gateware: gate all outputs on GC_ON — when GC_ON=0 the W5100S is unpowered (U12) and the GC is off, but FPGA banks stay at 3.3 V. Hold the W5100S bus and EXI outputs Hi-Z/low to avoid back-powering.
• Gateware: UART crossover — net names are FT-perspective (UART_TXD = FTDI output = FPGA RX on pin 18). Get this right in the board PCF.
• Gateware: EXI INT drive style — prefer open-drain emulation (drive low / release) on J3.3 rather than push-pull high.

Broader items (beyond the wiring review — block fab on the first two)

• Write the re-bba-rb pin constraints — exi_bba/synth.py still targets the iCEbreaker. This board: EXI on FPGA pins 3 (IOB_9b), 4 (IOB_8a), 44 (EXI_CLK, G6), 45 (EXI_CS), 46 (EXI_INT); W5100S bus on the IOT bank (23–43); CLK12 on 20 (G3); GC_ON on 21; ETH_RST on 2; UART on 18/19. This is where the DO/DI swap and the UART crossover (UART_TXD = FTDI output = FPGA RX) get resolved. Pure software; do it before ordering to prove the pinout.
• Add debug provisions — the board currently has none. RGB0–2 are unconnected, no LEDs, no button, no test points; the CLAUDE.md bring-up plan (StatusPanel heartbeat/activity LEDs + BTN re-init) has nothing to drive. Spare IOBs: 6, 9, 10, 11, 12, 13, 47, 48. Add ≥2 LEDs (heartbeat, EXI activity), a 4–6 pin debug header (logic-analyzer access — EXI CLK/CS/MOSI/MISO are what you probe when enumeration fails), and test points on 3V3 / 1V2 / ETH_3V3 / GC_ON. Cannot be retrofitted.
• Verify mechanical fit — outline + finger geometry vs SP1ETH/ETH2SP1 references (per CLAUDE.md), RJ45 and USB-C protrusion vs the GC serial port bay opening. An earlier commit says "need to remeasure PCB outline"; sp1_test_plug validates pads only, not the envelope.
• SP1 12 V rail viability — VERIFIED against existing projects (2026-07-17). webhdx's IDE-EXI v2 for Serial Port 1 (which became the commercial M.2 Loader): "New switching power regulator supplies 3.3V@2A from 12V rail" (webhdx, gc-forever thread t=4843, 2021-08-28) — a shipping SP1 product powers an M.2 SATA SSD + RP2040 entirely from pin 5's 12 V through a buck, no external supply. That's the same architecture as this board at several times our load (~130 mA @ 12 V). webhdx moved from a linear regulator to a buck because the linear "was generating a lot of heat" — validating the TPS562201 choice. The official modem (DOL-014) was the original 12 V consumer; SP1ETH leaves 12 V unused (runs from the 3.3 V pins). Remaining bench check only: - [ ] inrush into C65 (100 µF) + 2×10 µF buck input caps at GC power-on (the M.2 Loader precedent suggests this is a non-issue).
• Decide FT2232H EEPROM contents + flashing workflow — blank 93LC46B enumerates with default VID/PID (works, generic); custom VID/PID/serial/product string needs FT_PROG provisioning. Tied to the iceprog-pin-mapping decision above (changes the schematic).
• CC1/CC2 have no ESD protection (USBLC6 covers D+/D− only) — optional, most hobby designs skip; note spare-channel budget if respinning D2 area.
• Ensure hardware/re-bba-rb/.history/ (contains an embedded .git) is gitignored and never committed.

Minor / BOM

• RSET_BG: datasheet says 12.3 kΩ 1 % (ref schematic: 12 k + 300 Ω); board has 12.4 k (~0.8 % off). Match if convenient.
• Crystals Y1 (FTDI 12 MHz) and Y2 (W5100S 25 MHz): 18 pF load caps are correct only for CL ≈ 12 pF crystals — pick parts accordingly (W5100S Table 9 recommends CL = 12 pF).
• 12 V-rail parts ≥ 25 V rating: C3, C4 (10 µF 0805), C6, C65 (100 µF electrolytic); D3 SMAJ12A already correct.
• 1 % tolerance required: R1/R2 (buck VFB divider, TI requirement), R10 (FTDI REF 12 k), R16 (RSET_BG), R3/R4 (PR1 divider).
• TPS22810 CT: floating = fastest ramp (~0.7 A inrush into ETH rail caps). Consider CT = 10 nF footprint (DNP-able).
• Verify HR911105A internal LED pinout (assumed: 9/12 anodes via R14/R15 330 Ω to ETH_3V3, 10/11 cathodes to LNKn/ACTn) and the Bob-Smith common on pin 8 (tied straight to GND here; WIZnet ref separates chassis via 1 nF/2 kV — acceptable choice, confirm intent).
• Confirm at bring-up (from CLAUDE.md): W5100S register addresses / MR bits were written from memory.

JLCPCB ordering notes (DRC clean — these are order-form options)

• Stackup = JLC04121H-7628 (matches the 0.2104 mm prepreg / 0.6 mm core, ~1.14 mm ≙ JLC nominal 1.2 mm — satisfies the SP1 slot's 1.2 mm spec).
• Select ENIG (file has copper_finish "None") and gold fingers + 45° bevel for the SP1 edge connector.
• Hand-solder / non-economic-assembly parts: C65 (THT electrolytic), J2 magjack (THT), J1 USB-C, D2 (DFN2111-7, tiny). Plan assembly split.
• Add LCSC part numbers to symbol fields for JLC PCBA BOM export; check fiducials for SMT.

Housekeeping (repo) — done 2026-07-17

• Restored hardware/re-bba-rb/datasheets/ (deleted by 3547302) from the LFS store; added TPS22810 (power/) and PUSB3AB6 (exi/) datasheets that were missing from the original set.
• Deleted stale lowercase power.kicad_sch (the pre-rework draft from the first power-sheet commit; live sheet is Power.kicad_sch). It "kept coming back" because both paths were git-tracked: on a case-insensitive (Windows) checkout they are one file on disk, so deleting one path also deletes the other, and restoring the live sheet re-materialises both — the next commit resurrects the stale path. Removing the lowercase path from the git index (done from the case-sensitive devcontainer) is the permanent fix. Never add two files differing only in case.
• Deleted re-bba-rb.kicad_pcb.old.kicad_pcb / .old.kicad_pro leftovers (recoverable from git history if ever needed).

Verified correct — do not re-flag

TPS562201 (EN at 12 V legal, abs max 19 V; 0.768 V ref × 33k/10k = 3.30 V; L/C per Table 7-2) · TPS2116 mode/ST logic (GC priority, USB fallback, GC_ON polarity) · AP2112K ×2 · TPS22810 EN (never floats, R5 pull-up) · FT2232H VPHY/VPLL on 3.3 V is correct per datasheet (the VCORE→3V3 relabel at HEAD was a fix) · W5100S parallel-mode straps (MOD=0100, SCLK→GND, pin32=A0/pin33=A1, INTn push-pull, internal pull-ups on CSn/RDn/WRn/DAT) · W5100S 1V2 loop + mandatory 1 MΩ crystal feedback · PUSB3AB6 pinout/footprint · USB-C CC/ESD wiring · iCE40 power/config/flash, CLK12 on G3, EXI_CLK on G6 · magjack transformer spec (1:1, 350 µH) · PCB vs JLCPCB capability floor (rules in re-bba-rb.kicad_dru, 0 DRC errors).