Reference / Paper · 2026
Clockwork PicoCalc — Deep Dive Reference
- clockworkpi
- picocalc
- deep dive
- firmware
- assembly
Reference / Paper · 2026
Clockwork PicoCalc — Deep Dive Assembly, hardware, firmware, programming stacks, and gotchas Jeff Swan · Hack Tools project 2026-05-02 Clockwork PicoCalc — Deep Dive Authoritative reference for assembly, hardware, firmware, programming stacks, and gotchas. Companion docs: ../CLAUDE.md (project state), ../DEVELOPMENT.md (toolchain), ../01-about-me/bringup_checklist.md (day-one playbook). Last revised 2026-05-02. This doc is variant-agnostic — calls out Pico 1 (RP2040) vs Pico 2 (RP2350) vs Pico 2 W (RP2350 + Wi-Fi/BLE) wherever they diverge. Items I couldn't confirm during research are marked (unconfirmed) so they don't propagate as fact. Table of contents 1. TL;DR 2. Kit contents 3. Assembly walkthrough 4. Hardware tour 5. Default firmware & the multi-boot SD system 6. Programming stacks 7. Display & keyboard programming 8. PIO state machines on PicoCalc 9. Audio 10. Project ideas (broken out by focus area) 11. Known issues & errata 12. Resources 1. TL;DR The PicoCalc is a $75 retro-style handheld kit. A swappable Raspberry Pi Pico module sits in a socket on the ClockworkPi v2.0 carrier alongside a 4″ 320×320 IPS LCD, a 67-key backlit QWERTY keyboard, dual speakers, an SD slot, an AXP2101 PMU, and 8 MB external PSRAM. The keyboard is driven by an STM32F103 coprocessor that the Pico talks to over I²C. The kit ships flashed with a multi-boot SD bootloader and ~8 ready-to-run UF2 images (PicoMite BASIC, uLisp, FUZIX, NES emulator, MP3 player, Phyllosoma, picolua, Picoware) — pick one at boot and it loads from the card without USB. Programming target = whatever the swappable Pico in the socket is. Default kit ships with Pico 1 H (RP2040), but the same case takes Pico 2 (RP2350) or Pico 2 W (RP2350 + CYW43439 Wi-Fi/BLE). Latest Pico SDK 2.x supports all three via PICO_BOARD=pico| pico2|pico2_w. 2. Kit contents What ships in the standard 2026 box (per official kit page; confirm against the parts list inside): • • • • • • • • ClockworkPi v2.0 mainboard (carrier PCB) Raspberry Pi Pico module pre-fitted in the socket. Default is Pico 1 H (RP2040, 264 KB SRAM, 2 MB flash). Some current SKUs ship Pico 2 (RP2350) or Pico 2 W instead — read the silkscreen on the module. 4-inch 320×320 IPS display, SPI interface, with tempered-glass cover QWERTY backlit keyboard (membrane + STM32F103-driven controller PCB) with number row, function keys (F1–F10), four-way D-pad, ESC/BREAK Dual speakers ABS plastic shell halves + 2.5 mm hex key 32 GB microSD pre-loaded with the official multi-boot bundle Not included: 2× 18650 lithium-ion cells, USB-C cable 3. Assembly walkthrough Vendor claims a few minutes with no soldering. Real assembly is mostly screw-driving — but there are three failure modes that have killed units on the forum, so don't skim: 3.1 Battery selection • 2× 18650 cells, 18 mm Ø ±0.5, 65–69 mm length. • Brand-name only. Samsung 35E (3500 mAh) or 30Q (3000 mAh, higher current draw), Panasonic NCR18650B/G, LG MJ1. Anything claiming ≥4000 mAh is fake. • Buy from 18650batterystore.com, illumn.com, or IMR Batteries. Do not trust Amazon or AliExpress for these. • The on-board AXP2101 provides over-voltage / over-current / over-temp protection, so unprotected cells are acceptable. Protected cells fit if total length ≤69 mm. • Flat-top OR button-top both fit; flat-top requires extra polarity care (no ridge to bias against). 3.2 Battery polarity (IMPORTANT) Multiple forum reports of users reverse-installing one cell and bricking the AXP2101. Check the silkscreen markings carefully — they're not always strongly contrasted. The AXP2101 has limited reverse protection. If the PMU is killed, replacement is possible but requires fresh eFuse configuration — see forum thread "AXP2101 PMU eFuse configuration after replacement" before attempting. 3.3 Mainboard + keyboard + LCD • LCD ribbon: lift the FFC connector latch, insert with contacts down, latch closed. Don't force. • Speaker JST: keyed but verify before mating. • Keyboard FFC: another lift-latch-and-seat. Make sure it's all the way home. • Pico module: pre-fitted in the kit. If you ever swap it, the socket pinout is mirrored from the standard Pico when viewed from the front — DigitalDreams' corrected diagram lives in forum thread #17456 ("Core socket pinout"). Easy to flip 180° if you don't check. • BOOTSEL on the Pico is reachable through the rear grill of the case (toothpick or thin card). 3.4 Smoke test With cells seated and shells closed, long-press the power button (top-right of keyboard) ~1 second. Backlight comes on, splash shows PicoMite (default UF2) or the multi-boot menu. If nothing: USB-C may charge the cells enough to boot in a few minutes. 4. Hardware tour Subsystem Detail MCU Whichever Pico is in the socket: Pico 1 / Pico 2 / Pico 2 W. See §4.1. STM32F103R8T6, scans the matrix, manages the power button, LCD backlight, keyboard backlight, and battery telemetry. I²C slave at 0x1F. Bus speed must be 10 kHz for reliable comms (per DeepWiki). Source under Code/picocalc_keyboard/ in the official repo. Build with Arduino IDE + STM32duino, or STM32CubeIDE. GPL v3. Latest stable BIOS = 1.4; uLisp v1.1 currently only runs on 1.2 — don't auto-upgrade if Lisp matters. X-Powers AXP2101 — single-cell PMIC with on-board EGauge fuel gauge, 4 DC-DC converters, 11 LDOs, OVP/OCP/OTP. Reverse-polarity is not fully protected. 8 MB on the carrier, memory-mapped via the Pico's Keyboard MCU Keyboard FW PMU PSRAM Display Frame buffer Audio SD slot USB GPIO break-out QSPI/XIP. RP2350 has a dedicated XIP+PSRAM bus making this faster on Pico 2. Pico 2 W has on-module PSRAM too — collision/coexistence is (unconfirmed); check the forum before betting on both. 4.0″ 320×320 IPS, SPI. Driver IC commonly cited in community drivers as ILI9488 (320×320 region driven via partial-window mode); some older docs say "ILI9486." Confirm by reading the SPI init sequence in picocalc-textstarter/drivers/lcd.c. Frame rate ~30–60 Hz depending on SPI clock. 320×320 × 16 bpp = 204,800 bytes. Does not fit alongside meaningful program state in RP2040's 264 KB SRAM — community C drivers render in stripes/tiles or use the 8 MB PSRAM. Fits trivially in RP2350's 520 KB. Stereo PWM only — left=GP26, right=GP27. They share a PWM slice → both channels are forced to the same frequency, so true stereo is impossible without an external I²S DAC. (Forum #18339 "Audio with PIO PWM" has a workaround.) SPI-attached (not SDIO). Default layout = MBR with FAT32 main partition + 32 MB raw tail partition (FUZIX root). Cards >32 GB work if reformatted FAT32 (factory exFAT must be replaced). USB-C on the case routes to the Pico module's native USB. Appears as the Pico's BOOTSEL drive + serial port. Charging via VBUS goes through the AXP2101. Side-header exposes the Pico's free GPIO not consumed by display/SD/keyboard/audio. Per-pin map: see DigitalDreams' diagram in forum #17456. 3.3 V rail measures ~0.9% low under load on his unit — use external Vref for ADC accuracy. 4.1 Pico variants — what changes Pico 1 (RP2040) Pico 2 (RP2350) Cores 2× Cortex-M0+ SRAM Flash Wireless 264 KB 2 MB none 2× Cortex-M33 + 2× Hazard3 RISCV (pick at boot) 520 KB 4 MB none Pico 2 W (RP2350 + CYW43439) same as Pico 2 520 KB 4 MB Wi-Fi 4 (2.4 GHz) + BLE 5.2 Frame buffer fits in SRAM? No (use stripes or PSRAM) Yes (with room to spare) Yes PICO_BOARD= pico pico2 pico2_w Pico SDK version min TrustZone-M Notable extras any 1.x or 2.x 2.x 2.x — — yes XIP cache, PSRAM bus, FPU yes + CYW43 driver in SDK Practical implications: for any C app that wants a full-screen frame buffer, Pico 2 is much easier. Pico 1 forces you into stripe-rendering or PSRAM tricks. For wireless work (Bruce/Marauder-style projects, Picoware, Wi-Fi tools, BLE, MQTT) you need Pico 2 W. 4.2 Upgrading the Pico module The ClockworkPi v2.0 mainboard's Pico socket is the design's secret weapon — the Pico is not soldered, so you can swap modules in <60 seconds without touching firmware on the carrier. This makes the upgrade path low-risk and cheap. Useful to understand before you commit to one. 4.2.1 Why upgrade — concrete reasons Stay on Pico 1 H (the default) if: • • • • Your projects are text/menu/REPL-driven (PicoMite, uLisp, FUZIX, picolua, terminal apps). You're not pushing graphics beyond stripe rendering. You don't need wireless. You want maximum community-tested code paths — Pico 1 has the deepest install base. Upgrade to Pico 2 (RP2350, no wireless) when you hit one of: • • • • Frame buffer pressure. You want to write a graphics-heavy app — emulator, paint program, scope UI, sprite-heavy game — and stripe rendering is making the code ugly. Pico 2's 520 KB SRAM lets uint16_t fb[320][320] (~200 KB) live as a normal global with 300+ KB still free for state. FPU / DSP work. RP2040 has no hardware FPU; every float multiply is a software call. Pico 2's M33 has single-precision FPU + DSP extensions — anything signal-processingflavored (FFT for audio, demodulation for an SDR-companion role, real-time filtering) gets 5–20× faster. More PIO. RP2040 has 8 state machines across 2 PIOs; RP2350 has 12 across 3. Matters when you're combining a logic analyzer + PIO PWM + custom protocol on the same device. Larger code/asset budget. 4 MB flash vs 2 MB. Doubles room for fonts, sprite atlases, ROMs in flash, embedded data. • • • Faster XIP / dedicated PSRAM bus. Random reads from the carrier's 8 MB PSRAM are noticeably faster than going through RP2040's QSPI XIP. If you're using PSRAM for full FB, this is real. RISC-V option. Pico 2 lets you boot Hazard3 RISC-V cores instead of M33. Mostly curiosity territory unless you have a specific use. Future-proofing. TrustZone-M, secure boot, glitch detector. Lab toys today, useful tomorrow. Upgrade to Pico 2 W (RP2350 + CYW43439) when: • • • • Everything Pico 2 gives, plus you want Wi-Fi 4 (2.4 GHz, 802.11n, single-band) or BLE 5.2. You want to run Picoware (the bundled wireless-tools custom firmware) without external modules. You want to build any of the §10.3 wireless project ideas — Wi-Fi auditing on your own networks, MQTT telemetry, BLE sniffing, an OTA update path, network-timesynced apps. You want to drop the deep-dive's "Wi-Fi/BLE on side-header module" workaround and just use what's on board. Don't upgrade if you only need wireless occasionally — an external ESP32 module or nRF52 breakout on the side header costs $5–10, gives you better RF specs than the CYW43439, and keeps your Pico module on RP2040 for compatibility with the broadest community library set. Pico 2 W's wireless is convenient, not lab-grade. 4.2.2 What you give up by upgrading • Some PicoCalc-specific UF2s lag behind on Pico 2 / Pico 2 W — the SD bundle's /pico1apps/ directory is years older than /pico2-apps/. Verify the UF2s you actually use (PicoMite, uLisp, your own apps) all have current Pico 2 builds before you commit. Most do; some hobbyist forks don't. • Pico SDK 2.x required. If you have any locally-built C code that pinned to SDK 1.5 or earlier, it'll need a small port to 2.x. Public starters (picocalc-text-starter, etc.) are already on 2.x. • Pico 2 W only: on-module PSRAM coexistence with the carrier's 8 MB PSRAM is (unconfirmed) — read the forum before relying on the full 8 MB. • uLisp v1.1 currently only validates on Pico 1. (Combined with the BIOS 1.2 requirement, Lisp users should keep a Pico 1 H around even if they own a Pico 2 for everything else. The socket makes "swap to Pico 1, boot uLisp, swap back" a 30-second operation.) • Power draw. Pico 2 W with active radio is ~70–250 mA depending on activity vs Pico 1's idle ~25 mA. Battery life on 2× 18650 stays multi-hour, but it's a real difference in always-on scenarios. 4.2.3 Cost & where to buy Module Typical price Source Pico 1 H Adafruit (#5525), DigiKey, $5 Pico 2 $5 Pico 2 H (headers) Pico 2 W $7 $7 Pico 2 WH (wireless + headers) $9 Mouser, PiHut, Pimoroni Adafruit (#6202), DigiKey, Mouser DigiKey, Mouser Adafruit (#6210), DigiKey, Mouser DigiKey, Mouser Get the H/WH variant — Pico 2 / 2 W ship without headers by default and you'd need to solder them yourself. The PicoCalc socket needs through-hole male headers. Adafruit part numbers above are H/WH where it matters. 4.2.4 Physical swap procedure The whole operation is sub-minute. ESD precautions (touch grounded metal, work on a dissipative mat if you have one) — Pico modules are robust but not invulnerable. 1. 2. 3. 4. 5. 6. 7. 8. Power off. Long-press the keyboard's power button until the screen blanks. Don't trust "asleep" — fully off. Disconnect USB-C if plugged. Open the rear shell — 2.5 mm hex screws (the same ones from assembly). Lift the existing Pico module straight up out of the socket. It's a 2× 20-pin header arrangement; pull evenly on both ends to avoid bending pins. A small flat-head pry can help if it's snug — go gentle, alternate sides. Check orientation of the new module. The PicoCalc socket pinout is mirrored from the standard Pico orientation when viewed from the front. DigitalDreams' diagram in forum thread #17456 ("Core socket pinout") is the canonical reference. The microUSB / USB-C end of the Pico module faces the rear grill (BOOTSEL access). Get this wrong and you'll short rails — confirm before pressing down. Seat the new module evenly. Press down on both header rows simultaneously, not one end at a time. The pins should fully bottom out — about 5 mm of pin showing above the socket is normal. Don't reattach the shell yet. First do a smoke test: – With cells still in (or USB-C connected for power), long-press power. – Backlight should come on. – The multi-boot menu should appear (or boot to PicoMite). – If the screen stays dark, check orientation — pull the module, rotate 180°, reseat. Reattach the shell. 4.2.5 Software changes after upgrade Once the module is swapped, three things change: 1. PICO_BOARD= in your CMake. Replace -DPICO_BOARD=pico with -DPICO_BOARD=pico2 (Pico 2) or -DPICO_BOARD=pico2_w (Pico 2 W). Rebuild every C/C++ project. cd ~/pico/picocalc-text-starter rm -rf build && mkdir build && cd build cmake -G Ninja -DPICO_BOARD=pico2 .. ninja # or pico2_w 2. SD folder for UF2s. Pico 2 binaries go in /pico2-apps/ on the SD card, not /pico1apps/. The multi-boot loader picks the right folder based on which silicon is detected at boot. UF2s built for pico will not run on pico2 — the Cortex-M0+ instruction set is a strict subset of M33 in many ways but the binary format and boot sequence differ. 3. MicroPython UF2. Replace micropython_pico.uf2 with micropython_pico2.uf2 or micropython_pico2w.uf2 from LofiFren's repo. The Python code on top usually works unchanged. You can keep both pico1-apps and pico2-apps populated on the SD — useful if you swap modules occasionally. The bootloader auto-routes. 4.2.6 Recommended upgrade decision tree Will any of your real upcoming projects do one of: (a) full-screen frame buffer with sprites/animation, (b) FPU-heavy DSP / FFT, (c) >2 MB embedded assets, or (d) Wi-Fi/BLE without an external module? ├── No → stay on Pico 1 H. Largest community library set, lowest config friction. ├── Yes (a/b/c only, no wireless) → Pico 2 H. ~$7. Drop-in. └── Yes (d, plus optionally any of a/b/c) → Pico 2 WH. ~$9. Drop-in. If you're unsure: stay on Pico 1 H. The socket means you can upgrade later in literally one minute when a specific project demands it. Don't pre-emptively buy a Pico 2 W "just in case" — buy it when a concrete project is gated on it. 5. Default firmware & the multi-boot SD system 5.1 What ships flashed • Pico's internal flash: bootloader_pico.uf2 (uf2loader by pelrun, originally adwuard/Picocalc_SD_Boot — pelrun's fork is now canonical). • That bootloader looks at the SD card on power-on. If a multi-boot menu config is present and the user holds Up (or F1 / F5) at boot, it shows the menu. Otherwise it auto-loads the last-launched UF2. • Fallback if SD missing or unreadable: PicoMite, also baked in. 5.2 SD layout (since v0.6) / FAT32 ├── BOOT2040.uf2 The menu UI itself ├── pico1-apps/ UF2s for RP2040 boards │ ├── PicoMite_v6.02.01b4_beta.uf2 │ ├── PicoCalc_uLisp_v1.1.uf2 │ ├── PicoCalc_NES_v1.0.uf2 │ ├── PicoCalc_MP3Player_v0.5.uf2 │ ├── picolua.uf2 │ ├── phyllosoma_kb.uf2 │ ├── Picoware_v1.6.9.uf2 │ └── ... ├── pico2-apps/ (or merged folder — varies by bundle) └── (unallocated 32 MB raw) FUZIX rootfs (last partition) The first entry in [brackets] in the menu = the last-launched "default app." Subsequent power-ons skip the menu unless you hold the Up key. 5.3 Where to download • Releases: https://github.com/clockworkpi/PicoCalc/releases — full SD bundles • Bootloader source: https://github.com/pelrun/uf2loader 5.4 Adding your own UF2 to the menu Drop the file into /pico1-apps/ (or /pico2-apps/ per variant), eject, reboot. The bootloader scans the directory at boot — no manifest editing required for current revisions. 5.5 Recovering the bootloader after a BOOTSEL flash If you BOOTSEL-flash a custom UF2 directly to the Pico's flash, you've overwritten bootloader_pico.uf2. To restore the multi-boot menu: 1. 2. Hold BOOTSEL, replug USB, drag bootloader_pico.uf2 from the SD release back onto the BOOTSEL drive. Power-cycle. Multi-boot is back. This is why dropping UF2s on the SD card is the preferred iteration loop once dev is set up — no flash overwrite, no BOOTSEL gymnastics. 6. Programming stacks The PicoCalc is famously promiscuous about languages. What follows is what's actually working today, with install steps. None of these require giving up the others — the multiboot SD lets you switch by holding Up at power-on. 6.1 Pico SDK in C/C++ — first-class The canonical low-friction starter is BlairLeduc/picocalc-text-starter — its drivers/ folder has battle-tested LCD, keyboard, audio, SD, and STM32 southbridge code with printf/scanf retargeted to display + keyboard. Use this rather than rolling your own. Install: # Linux deps sudo apt install cmake gcc-arm-none-eabi libnewlib-arm-none-eabi build-essential ninja-build # SDK + starter mkdir -p ~/pico && cd ~/pico git clone -b master --recurse-submodules https://github.com/raspberrypi/picosdk.git git clone https://github.com/BlairLeduc/picocalc-text-starter.git git clone https://github.com/clockworkpi/PicoCalc.git # for keyboard FW source export PICO_SDK_PATH=$HOME/pico/pico-sdk # Build, choosing variant: cd picocalc-text-starter mkdir build && cd build cmake -G Ninja -DPICO_BOARD=pico .. ninja # add to ~/.bashrc # or pico2, pico2_w Resulting .uf2 → SD /pico1-apps/ (or /pico2-apps/). Key wiki: https://github.com/clockworkpi/PicoCalc/wiki/Setting-Up-the-Pico-SDK-onLinux-for-Pico-Development. See §7 below for the actual driver API. 6.2 MicroPython — best for prototyping The PicoCalc-aware fork by Lofi Fren wraps the display, keyboard, and SD drivers as native MicroPython modules. Three prebuilt UF2s — pick the one that matches your Pico: • • • micropython_pico.uf2 (RP2040) micropython_pico2.uf2 (RP2350) micropython_pico2w.uf2 (RP2350 + Wi-Fi/BLE) Install: hold BOOTSEL, plug USB, drag the UF2. Connect with Thonny (set interpreter = "MicroPython (Raspberry Pi Pico)") or mpremote: pip install --user mpremote mpremote connect auto repl mpremote cp app.py :main.py # interactive # push to device, runs on boot Repo: https://github.com/LofiFren/PicoCalc. Trade-off vs C: ~10–50× slower, no PIO assembler, can't use most pico-sdk helpers directly. Fine for UI/logic; bad for tight DSP or signal work. 6.3 PicoMite (MMBasic) — default firmware Geoff Graham's PicoMite has an explicit PicoCalc target. It's a complete BASIC interpreter with file I/O, graphics primitives, FFT, sound, sprites — the kind of "BASIC + everything you wished BASIC had" that makes it a serious development environment, not just a toy. v6.02.01b4 ships pre-loaded on the SD card. • • Authoritative: https://geoffg.net/picomite.html PicoCalc-tweaked sources: https://github.com/cuu/PicoMite, https://github.com/madcock/PicoMiteAllVersions Reach for PicoMite when you want a self-contained on-device dev environment with no host computer in the loop. 6.4 uLisp — Common Lisp on the metal Active on PicoCalc with display + keyboard support. Currently only works on BIOS 1.2 of the keyboard FW; BIOS 1.4 compatibility is WIP. If Lisp is a serious goal, hold off on BIOS upgrades. • • • UF2: PicoCalc_uLisp_v1.1.uf2 from the releases page Build from source: Code/uLisp/ in the official repo Docs: http://www.ulisp.com/show?56ZO= and forum thread #17107 6.5 picolua — Lua REPL with graphics + SD Multiple maintained forks. Most active right now is Lana-chan/picocalc_lua (RP2350 support added; commit 4778a8f notes a low-power-sleep hang as a known issue). • • • https://github.com/cuu/picocalc_lua (original) https://github.com/Lana-chan/picocalc_lua (RP2350) https://github.com/benob/picocalc_lua (alt) 6.6 Rust — embassy-rp + rp-hal Both crate ecosystems target both RP2040 and RP235x. There is no PicoCalc-specific BSP crate that I could confirm — the awesome-pico-calc list has a "Rust driver" entry but the link wasn't surfaceable during research, so treat it as (unconfirmed). Practically: start from a Pico/Pico 2 BSP, port the LCD + keyboard drivers (the C code in picocalc-text-starter is small enough to translate). • • https://github.com/embassy-rs/embassy https://github.com/rp-rs/rp-hal 6.7 TinyGo — Go on the Pico Confirmed working — the forum has a worked example: "Hello World and RPN Calculator implemented in TinyGo." No dedicated PicoCalc target in the TinyGo BSP; uses the generic pico / pico2 targets and you bring your own LCD/keyboard code. • • https://tinygo.org Forum thread: https://forum.clockworkpi.com/t/hello-world-and-rpn-calculatorimplemented-in-tinygo/20834 6.8 NuttX RTOS — port in progress Active porting effort. SD/SPI/I²C/PWM/audio/UART working on RP2350; LCD + keyboard pending as of late-2025 forum activity. Watch this if you want a real preemptive RTOS instead of MicroPython's GIL-y world. • Status thread: https://forum.clockworkpi.com/t/nuttx-rtos-on-picocalc/16783 6.9 FUZIX — mini-UNIX in 32 MB Lightweight Unix-like OS. Ships in the default SD bundle and lives on the 32 MB raw partition. Boots a /bin/sh, has a small set of UNIX userland tools, runs in either RAM-only or with a writable rootfs on SD. • UF2: PicoCalc_Fuzix_v1.0.uf2 in releases 6.10 Phyllosoma — compiled BASIC Faster than PicoMite (compiled vs interpreted). Full keyboard support. Less famous, but worth a look if PicoMite's interpretive overhead bites a particular project. • UF2: phyllosoma_kb.uf2 in the SD bundle 6.11 Picoware — MicroPython-based custom firmware Higher-level "everything bundled" custom firmware: Wi-Fi tools, BLE, social-media clients, games. Useful baseline if you have a Pico 2 W and want to skip the integration step. • Forum: https://forum.clockworkpi.com/t/picoware-open-source-custom-firmware/ 18536 6.12 What's missing • No JavaScript port found that targets PicoCalc specifically. (mJS/Espruino runs on Pico generically; nobody has wrapped the LCD/keyboard.) • No CircuitPython port found — Adafruit's CircuitPython runs on Pico 1/2/2W generically, but no PicoCalc display/keyboard drivers. • No native Linux on the standard Pico. To run Linux on this case, swap the Pico module for a Pi Zero 2 W carrier (community calls this "PicoCalc Trixie" or "ZeroCalc"), or for a LuckFox Lyra SoM. Both fit the same socket. Treat as a separate project. 6.13 Stack picker (heuristic) You want… Pick Most on-device productivity, zero PicoMite host computer Fastest iteration with host-side push Maximum performance, deterministic timing, PIO Lisp Compiled-BASIC speed A real RTOS Pocketable Linux Modern systems language MicroPython (LofiFren) Pico SDK C/C++ uLisp (lock BIOS at 1.2) Phyllosoma NuttX (when port lands) Swap the Pico for Pi Zero 2 W or LuckFox Lyra Rust (embassy) or TinyGo 7. Display & keyboard programming The reason picocalc-text-starter is the canonical reference: it consolidates the perperipheral drivers into a single picocalc.h umbrella that retargets newlib's stdio. Once picocalc_init(NULL) runs, printf/scanf go to the LCD + keyboard, and fopen/fwrite go to the SD card. 7.1 The starter's driver layout picocalc-text-starter/ ├── drivers/ │ ├── picocalc.h # umbrella header │ ├── lcd.c / lcd.h # SPI display driver │ ├── keyboard.c / .h # I2C reader against STM32 │ ├── audio.c / .h # PWM tone generation │ ├── southbridge.c / .h # STM32 power/backlight control │ └── clib.c # newlib retargets (stdio, file IO) └── src/main.c # demo REPL 7.2 Public API (sketch — exact signatures evolve) #include "picocalc.h" int main(void) { picocalc_init(NULL); // SPI, I2C, SD, audio, stdio retarget printf("\x1b[2J\x1b[H"); // ANSI clear screen + home cursor printf("Hello, PicoCalc!\n"); int c = getchar(); // blocks, reads from keyboard printf("You pressed: %d\n", c); while (1) tight_loop_contents(); } The terminal layer understands a useful subset of ANSI escape codes (cursor, color, clear). For graphics, drop down to lcd_* calls in lcd.h. 7.3 Keyboard event model • STM32F103 scans the matrix and pushes key events into a small FIFO. • Pico polls the STM32 over I²C at 10 kHz bus speed (above 100 kHz drops bytes — confirmed by DeepWiki troubleshooting). • Reads are request/response: write the "fetch key" register, read 2 bytes (keycode + modifier). • Function keys (F1–F10), arrow/D-pad, ESC, BREAK each have ASCII-extended codes — exact map is in keyboard.c of text-starter or in Code/picocalc_keyboard/include/keymap.h of the official repo. • Backlight (LCD + keyboard separately) is set via dedicated I²C registers — not Pico GPIO. 7.4 Frame buffer strategies • RP2040 (Pico 1): 204,800 bytes is most of SRAM. Three options: a. Tile/stripe: keep an 8-row stripe in RAM, render scanlines into it, push, repeat. picocalc-text-starter does this for its text terminal. b. PSRAM full-FB: place the FB in the carrier's 8 MB PSRAM. Slower writes (~10– 20 MB/s vs ~50 MB/s for SRAM) but full random access. Helpful for spriteheavy graphics. c. DMA chains: build the line in SRAM, DMA it out over SPI, prepare next line while it transmits. Effective for video-rate updates if SPI clock is high enough. • RP2350 (Pico 2 / Pico 2 W): full 320×320×16 fits in SRAM with 300+ KB to spare. Just allocate it. 7.5 LVGL / GUI library awesome-pico-calc lists an LVGL integration. LVGL gives you proper widgets, themes, animations — appropriate for menus, settings UIs, instrument-style displays. Heavier than rolling your own. The DeepWiki has a programming-guide section on LVGL on PicoCalc. 8. PIO state machines on PicoCalc The RP2040/RP2350's PIO is the platform's superpower — 8 (RP2040) or 12 (RP2350) tiny state machines that run independently of the CPUs at up to the system clock rate. PicoCalc-specific applications: • • Audio output via PIO PWM (forum #18339) — workaround for the GP26/GP27 single-PWM-slice limitation. PIO time-multiplexes the two outputs. Custom display drivers — currently the LCD goes through the RP2040 SPI peripheral. PIO-driven SPI can hit higher clocks if you're willing to work for it. • • • PicoDVI / DispHSTX (RP2350) — luke-wren's PicoDVI outputs HDMI from the RP2040 via PIO; on RP2350 the HSTX peripheral does it natively. Nobody's wired this to PicoCalc's side header yet, but the GPIOs are exposed. Logic-analyzer style sampling — PIO can capture pins at >100 MS/s and push to RAM via DMA. Useful for the "hand-held protocol sniffer" project category (§10). Bit-banged custom RF modulation — PIO can synthesize OOK/FSK/Manchester at audio-to-MHz rates, output to a GPIO routed to an external transmitter. The PicoCalc isn't a Flipper, but with an external CC1101 / nRF24 module on the side header, PIO + the keyboard + the screen makes a respectable signal-research handheld. PIO assembler reference: pico-sdk/pio/, the pico-examples repo's PIO directory, and Van H