RP2350 no-MMU Linux Buildroot ports

This tree builds tiny Buildroot-based Linux images for RP2350 RISC-V (Hazard3) boards. The original target is the Raspberry Pi Pico 2 / SparkFun Pro Micro RP2350 work; this branch adds an Adafruit Fruit Jam RP2350B bring-up target.

For a community getting-started walkthrough, see Linux on Fruit Jam by Mikey Sklar on Adafruit Playground.

Quick start after flashing

Flash the Fruit Jam UF2, then use the image from a serial console first. On the tested macOS host the USB CDC console appears as /dev/cu.usbmodem1101; the hardware UART header remains available at 115200 8N1 on GPIO8/GPIO9.

screen /dev/cu.usbmodem1101 115200

Once logged in, these commands show what the image can do:

fruitjam-services status
ls /root/berry /root/sh /root/rtttl
sh /root/sh/run-all.sh
berry-run /root/berry/run-all.be
berry-run /root/berry/run-visual.be
fruitjam-rtttl scale

The examples are intentionally part of the image:

• /root/berry contains Berry language and hardware examples, including the importable fruitjam hardware module, NeoPixel animations, USB HID decode, and direct sysfs/ADC/button reads.
• /root/sh contains shell examples for services, HTTP/CGI, NeoPixels, buttons, I2C, ADC, SD, DVI, USB-host status, WAV analysis, and small utility checks.
• /root/rtttl contains RTTTL tunes for the TLV320DAC3100 audio bring-up path.

To make the board reachable from another machine over the onboard ESP32-C6 AirLift, put WiFi credentials on the SD card and reboot:

mkdir -p /mnt/sd/fruitjam
chmod 700 /mnt/sd/fruitjam
cat > /mnt/sd/fruitjam/wifi.conf <<'EOF'
SSID=your-ssid
PASSWORD=your-passphrase
EOF
chmod 600 /mnt/sd/fruitjam/wifi.conf

After AirLift joins WiFi, airliftctl serve-inbound exposes the user-facing network surface directly through the coprocessor:

• http://<board-ip>/ serves /mnt/sd/www/index.html for user pages.
• http://<board-ip>/playground opens the built-in hardware playground.
• telnet <board-ip> 23 opens the tiny Fruit Jam shell.
• Passive FTP on <board-ip>:21 serves the SD card rooted at /mnt/sd, so /wavs is visible to FTP clients.

This is not a Linux wlan0 interface. It is a small AirLift/NINA userspace server for HTTP, telnet, and FTP; normal Linux sockets and the target-side wget still use the local loopback network.

Adafruit Fruit Jam RP2350B milestone

The Fruit Jam target is named adafruit_fruit_jam_rp2350. It uses:

• RV32 RISC-V Hazard3, no MMU.
• SMP disabled.
• BusyBox-centered userspace plus small no-MMU-friendly Fruit Jam tools.
• CramFS root filesystem in flash, with a 10 MiB flash partition reserved from 6 MiB through the end of the 16 MiB device.
• Kernel copied to 8 MiB external PSRAM.
• UART1 console on the Fruit Jam TX/RX pins (GPIO8/GPIO9), 115200 8N1.
• USB CDC ACM console on /dev/ttyGS0 when the gadget enumerates.
• USB CDC shells use standalone /usr/bin/hush. The hardware UART uses fruitjam-uart-login to wait for Enter before execing hush, avoiding a no-MMU respawn loop when nothing is attached to GPIO8/GPIO9. Telnet uses a tiny fruitjam-telnetd plus /usr/bin/fruitjam-shell so remote login does not require a large shell allocation, with a four-entry command history and command/path tab completion for telnet sessions. The experimental USB boot-keyboard shell has matching small history and command/path completion.
• Berry installed as /usr/bin/berry, including -e, script execution, and REPL.
• BusyBox vi.
• PIO-backed /dev/neopixels for the five onboard NeoPixels, plus /root/berry/neopixels.be as a small Berry smoke-test program.
• Legacy sysfs GPIO through gpiochip0 for GPIO0..GPIO45, including GPIO29 LED output and GPIO0/GPIO4/GPIO5 button inputs.
• microSD as /dev/mmcblk0//dev/mmcblk0p1, mounted at /mnt/sd as VFAT.
• fruitjam-buttons daemon watching GPIO0/GPIO4/GPIO5 and logging events to /mnt/sd/fruitjam/buttons.db.
• fruitjam-buttonlog, a tiny fixed-schema SQLite 3 file writer. It avoids the full SQLite CLI/library because the no-MMU target cannot reliably allocate a large SQLite-linked process after services are running.
• Tiny mosquitto_pub and mosquitto_sub compatible MQTT tools. They use normal Linux sockets by default, support username/password authentication for QoS 0 broker smoke tests, and --airlift routes the same requests through airliftctl mqtt-pub/mqtt-sub over the ESP32-C6 NINA TCP socket API.
• GPIO-backed Linux I2C master on GPIO20/GPIO21, exposed as /dev/i2c-0, plus the tiny fruitjam-i2c scan/ping helper.
• /dev/fruitjam-audio starts/stops PIO1-generated TLV320DAC3100 MCLK, BCLK, WS, and DIN signals on GPIO24-GPIO27. fruitjam-rtttl is the current audio bring-up helper and has microphone-confirmed audible RTTTL output.
• fruitjamctl GPIO diagnostics for USB-host power enable, shared TLV320/ESP32-C6 reset, and software BOOTSEL.
• airliftctl diagnostics for the onboard ESP32-C6 AirLift NINA coprocessor, including firmware/status/IP checks and a minimal outbound TCP HTTP fetch. AirLift SPI access is locked so a second airliftctl exits safely while the inbound service owns the coprocessor; read-only fw, mac, status, and ip commands fall back to the last values in /tmp/airlift-start.log.

Validated on hardware:

• USB CDC shell on /dev/cu.usbmodem1101.
• Hardware UART shell/log path on /dev/cu.usbserial-P97cvdxp.
• /proc/mtd reports mtd0: 00a00000 00001000 "cramfs".
• /sys/class/gpio/gpio29/value reads back output writes, and GPIO0/GPIO4/GPIO5 export as pulled-up inputs.
• AirLift inbound HTTP serves user pages from /mnt/sd/www at http://<board-ip>/ and the built-in hardware playground at http://<board-ip>/playground after WiFi is configured on the SD card.
• The optional loopback fruitjam-services core set can serve http://127.0.0.1/, http://127.0.0.1/playground, and CGI scripts; the tiny HTTP-only wget -O - implementation returns the CGI environment test.
• fruitjam-services init creates /mnt/sd/www/index.html with a small "Fruit Jam stuff" placeholder only when the SD card does not already have an index page. Users can replace that file with their own web page.
• The /playground page is a self-contained reactive Fruit Jam hardware playground. /cgi-bin/fruitjam.cgi exposes JSON actions for status, NeoPixels, button test events, RTTTL playback, WAV listing/playback, ADC reads, DVI rendering, USB-host status, I2C checks, explicit Berry example runs, and regular user .be files directly under /mnt/sd/berry. Hardware actions use direct C/tiny-helper paths; Berry is only invoked by the Berry runner.
• AirLift inbound telnet accepts a remote shell and echoed TELNET_OK. AirLift telnet sessions use a 60-second default idle timeout so a stale client does not monopolize the single no-MMU shell bridge; a new connection can preempt a stale idle session after 15 seconds.
• Default AirLift startup is wrapped by fruitjam-services airlift-monitor, which reruns the inbound server if it exits after leaving ESP32-C6 TCP sockets open, removes stale monitor PID files, and treats a missing inbound heartbeat for 60 seconds as a restart condition. The inbound server also recycles itself periodically and exits on listener accept failures so the monitor can reopen NINA sockets. Check /tmp/airlift-start.log for probe/join and restart messages.
• fruitjam-services status reports service processes and TCP/UDP listeners without spawning ps/netstat, avoiding the no-MMU fragmentation regression that previously broke CGI after status checks.
• AirLift inbound passive FTP lists, uploads, and downloads files under /mnt/sd. The optional loopback core service set also includes tiny FTP with PASV/EPSV and PORT/EPRT data modes plus TFTP daemons for target-side smoke tests.
• /proc/partitions reports mmcblk0 and mmcblk0p1; /mnt/sd is VFAT, writable, unmountable, and remountable.
• Synthetic button events written to /run/fruitjam-buttons.fifo are logged to /mnt/sd/fruitjam/buttons.db and mirrored in /mnt/sd/fruitjam/buttons.log.
• With /mnt/sd/fruitjam/buttons.conf set to MQTT_TRANSPORT=airlift, a synthetic button event published through mosquitto_pub --airlift and was received by a test MQTT broker as fruitjam/buttons/button2.
• /dev/i2c-0 is i2c-gpio0 on GPIO20/GPIO21; fruitjam-i2c scan found the TLV320DAC3100 control interface at 0x18.
• /sys/class/misc/fruitjam-audio registers as misc char device 10:125, and /dev/fruitjam-audio accepts start/stop; fruitjam-rtttl --loud --tone 880 2500 was verified with the Mac microphone helper.
• berry -e 'print("berry ok")'.
• Berry REPL expression evaluation.
• berry-run /root/berry/neopixels.be, visually confirmed on the onboard NeoPixels.
• /bin/vi -> busybox.
• fruitjamctl bootsel, verified by picotool info -a reporting boot type: bootsel.
• AirLift over RP2350 PL022/spidev hardware SPI: airliftctl probe reported NINA firmware 3.3.0, WiFi joined successfully, and airliftctl tcp-get example.com / returned HTTP 200 plus the response body. airliftctl mqtt-pub published a QoS 0 MQTT message over the same NINA TCP path to a local broker, which received fruitjam/test hello-from-airlift. mosquitto_sub and airliftctl mqtt-sub are now present for finite subscribe smoke tests, pending hardware verification on the current board.

AirLift is exposed as a userspace NINA socket helper, not as a Linux wlan0 network interface. The boot service starts airliftctl serve-inbound for external HTTP, telnet, and FTP when WiFi is available. The tiny target-side wget still uses normal Linux sockets, while airliftctl tcp-get, mosquitto_pub --airlift, and mosquitto_sub --airlift use the ESP32-C6 directly.

Fruit Jam hardware support matrix

Status means support in this Buildroot Linux image, not support in CircuitPython. Pin details come from the Adafruit Fruit Jam pinout and the local Fruit Jam pin map in docs/pinmap-fruitjam.md.

Hardware	Pins / device	Status	Current Linux support	TODO / notes
RP2350B RISC-V CPU	Hazard3 RV32	Supported	Boots Linux 6.15 no-MMU with SMP disabled.	Continue reducing memory pressure from larger userland tools.
External flash	16 MiB QSPI	Supported	Bootloader, kernel, DTB, and 10 MiB CramFS rootfs live in flash.	None for current boot path.
External PSRAM	8 MiB QMI/CS1 GPIO47	Supported	Kernel is copied to PSRAM by the bootloader.	No general Linux RAM expansion beyond current port design.
USB device console	RP2350 USB CDC, /dev/ttyGS0	Supported	Host sees /dev/tty.usbmodem1101; CDC shell is used by the smoke suite.	CDC console can be sensitive to repeated open/close churn.
UART console header	GPIO8 TX, GPIO9 RX	Supported	Hardware UART shell/log path at 115200 8N1.	Keep as fallback when USB or graphics work changes.
ROM BOOTSEL from Linux	RP2350 reboot command	Supported	fruitjamctl bootsel re-enters BOOTSEL and picotool info -a sees the ROM.	None.
BusyBox userspace	/bin, /usr/bin	Supported	BusyBox tools plus vi, hush, web/network helpers, free/uptime/du/fruitjam-mem, tiny ps/pgrep/pkill, and Fruit Jam tools.	Keep applets constrained for no-MMU allocation behavior.
Berry interpreter	/usr/bin/berry, /usr/bin/berry-run, /root/berry/fruitjam.be	Supported	berry -e, scripts, REPL, and an importable Fruit Jam hardware module for GPIO/buttons, ADC, I2C scan/ping, USB-host status through the kernel bridge when present, USB HID report decode, USB keyboard command helpers, AirLift diagnostics/TCP helpers, MQTT command helpers, device presence, audio clock, RTTTL/WAV command helpers, fruitjamctl board-control commands, DVI command writes, and NeoPixels; berry-run /root/berry/neopixels.be drives LEDs with lower cache pressure for multi-script runs. The playground can also list and run regular .be files from /mnt/sd/berry as SD: entries.	Extend the Berry module as more kernel helpers land.
Onboard NeoPixels	GPIO32, five LEDs	Supported	PIO-backed /dev/neopixels; Berry and CGI can update pixels.	None for basic color writes.
Buttons	GPIO0, GPIO4, GPIO5	Supported	Sysfs GPIO input, fruitjam-buttons, button log, CGI status, synthetic test events.	Physical edge logging should get longer soak testing.
Red LED / IR pin	GPIO29	Partial	LED control through sysfs/fruitjamctl; active-low output works.	IR receiver decoding is not implemented.
microSD card	GPIO34-39 SPI/MMC, CD GPIO33	Supported	/dev/mmcblk0p1 mounts at /mnt/sd as VFAT; read/write/remount verified.	Optional wider SDIO DAT1/DAT2 path is not implemented.
I2C / STEMMA QT	GPIO20 SDA, GPIO21 SCL	Supported	i2c-gpio0 as /dev/i2c-0; fruitjam-i2c scan finds TLV320 at 0x18.	Add kernel descriptions for more attached devices as needed.
ADC / analog header	GPIO40-GPIO47 ADC	Supported	fruitjam-adc reads ADC channels and internal temperature through sysfs.	Calibration/scale polish.
TLV320DAC3100 audio	I2C 0x18, GPIO24 DIN, GPIO25 MCLK, GPIO26 BCLK, GPIO27 WS	Partial	/dev/fruitjam-audio generates PIO clocks; fruitjam-rtttl configures the codec and microphone-verified RTTTL output works.	Full streamed PCM/I2S playback is not implemented.
ESP32-C6 AirLift	SPI GPIO28/30/31/46, READY GPIO3, IRQ GPIO23, reset GPIO22	Partial	NINA firmware 3.3.0; airliftctl can probe, scan, join WiFi, TCP GET, MQTT publish, and serve inbound HTTP/telnet/FTP.	Not a Linux wlan0 interface yet; normal wget still only uses Linux sockets.
HTTP user pages and playground	AirLift TCP/80; optional loopback HTTP	Supported	/ serves /mnt/sd/www/index.html; /playground serves the built-in hardware UI; /cgi-bin/fruitjam.cgi reports status and controls NeoPixels, RTTTL, WAVs, I2C, ADC, DVI, USB-host status plus bounded keyboard probes, buttons, built-in Berry examples, and user Berry files from /mnt/sd/berry. Hardware actions use direct C/tiny-helper paths.	Use http://<board-ip>/playground after AirLift joins WiFi, or fruitjam-services core for loopback tests.
Telnet service	AirLift TCP/23; optional loopback TCP/23	Supported	AirLift inbound shell and tiny fruitjam-telnetd/fruitjam-shell; telnet smoke tests pass.	Only one AirLift telnet session at a time.
FTP service	AirLift TCP/21 plus passive data 2121+; optional loopback TCP/21	Supported	AirLift passive FTP lists, uploads, and downloads files under /mnt/sd; FileZilla passive mode works. The optional loopback fruitjam-ftpd supports PASV/EPSV and PORT/EPRT, plus STOR/APPE/RETR/LIST/NLST/RNFR/RNTO/MKD/RMD/DELE.	Upload completion can be slow over the current NINA raw socket path.
TFTP service	Optional loopback UDP/69	Supported	BusyBox tftpd serves the TFTP area README when fruitjam-services core is started.	Not part of the default external AirLift service set.
USB host data	GPIO1 D+, GPIO2 D-	Experimental	USB host 5V can be switched, /dev/fruitjam-usbhost owns line state, reset timing, and PIO packet diagnostics, and the Linux HCD is configured with the wili8jam PIO0/SM0/SM1/SM2/DMA9/252 MHz settings. The HCD now auto-registers after an 8 second boot service window, power-cycles host 5V before registration, waits 500 ms after port reset before EP0 enumeration for the CH334F hub, and schedules an automatic power-cycle recovery after repeated EP0 failures. fruitjam-usbhost hcd-start remains available as an idempotent retry path. Kernel config enables hub, HID, evdev/joydev, and xpad/Xbox support.	Flash the current image and prove Logitech receiver plus Xbox360 gamepad enumeration with ./scripts/usbhost-hcd-smoke.py; live current-board proof is still required.
USB host 5V switch	GPIO11	Partial	fruitjamctl usb-power on/off controls power enable.	Keep power/reset behavior aligned with the Linux HCD path.
DVI / HSTX output	GPIO12-GPIO19, /dev/fruitjam-dvi	Partial	Tiny RGB332 HSTX DVI misc driver plus fruitjam-dvi text/dashboard/helper command output; hardware commands were verified on the flashed image.	Full fbdev/console is not implemented.
I2S data path	GPIO24 DIN, GPIO25 MCLK	Partial	Tiny generated-tone path exists for RTTTL and simple WAV tone tests.	Add complete streamed PCM driver/path.
IR receiver	GPIO29 shared with LED	TODO	No decoder.	Decide conflict/ownership with red LED.
ESP32-C6 native flashing from Linux	SPI/UART control path	TODO	Updated externally using Adafruit updater workflow.	Integrate a controlled in-image updater later.

Fruit Jam tool quick reference

The target keeps tools intentionally small because this is a no-MMU system where process size and memory fragmentation matter.

Tool or path	Purpose
fruitjam-services	Start, stop, restart, and inspect Fruit Jam services without large ps/netstat helpers.
fruitjam-telnetd	Tiny TCP/23 telnet shell service.
fruitjam-shell	Tiny command shell used by telnet sessions, with recent command history and command/path tab completion.
fruitjam-ftpd	Tiny FTP server rooted at /mnt/sd, with passive and active data modes for loopback service tests.
BusyBox httpd	Local web server and CGI runner under /www.
/cgi-bin/fruitjam.cgi	JSON hardware playground API using direct C/tiny-helper hardware actions, bounded USB keyboard probes, plus an explicit Berry runner.
BusyBox tftpd	TFTP server rooted at /tmp/tftp.
wget	Tiny HTTP-only client for normal Linux IPv4 sockets.
telnet	Tiny telnet client.
nc	Tiny bidirectional netcat-style TCP client/server.
/root/sh/serial-over-tcp.sh	Bridges a character device to a TCP port with nc.
fruitjamctl	Board diagnostics, reset controls, USB-host power, and software BOOTSEL. Berry exposes command builders and run wrappers for these board controls.
fruitjam-i2c	Scan or ping the GPIO-backed /dev/i2c-0 bus.
fruitjam-adc	Read RP2350 ADC inputs and the internal temperature ADC channel.
fruitjam-dvi	Render bounded text/dashboard/test frames to /dev/fruitjam-dvi.
fruitjam-wavplay	Analyze simple WAV files and play tone segments through the TLV320 tone path.
fruitjam-usbhost	Report USB host power and D+/D- line state, preferring /dev/fruitjam-usbhost when present, with json, wait, monitor, reset, decode, hid, parameterized kbd-init/kbd-poll, kbd-find, kbd-text/kbd-events, and kbd-shell/kbd-auto-shell boot-keyboard commands. The USB keyboard shell has a four-entry history and command/path tab completion. Berry exposes command builders and run wrappers for these keyboard probes.
fruitjam-hidkeys	Decode USB HID boot-keyboard 8-byte reports into text/events, including DATA0/DATA1 last_rx_hex packets from the PIO bridge when they contain an 8-byte keyboard report.
fruitjam-mem, free	Tiny no-fork memory, uptime, load, and commit-pressure summary from /proc.
fruitjam-uptime, uptime	Tiny no-fork uptime and load-average view from /proc/uptime and /proc/loadavg, with text and JSON output.
fruitjam-du, du	Tiny recursive disk-usage helper with summary/all/byte/json modes for SD/web/Berry file inspection.
fruitjam-ps, ps	Tiny no-fork process list from /proc, with text and JSON output.
fruitjam-pgrep, pgrep, pkill	Tiny no-fork process lookup/signaling from /proc using substring or exact matching, avoiding `ps
fruitjam-buttons	Button daemon for GPIO0/GPIO4/GPIO5 with log, FIFO, SQLite, and MQTT hooks.
fruitjam-buttonlog	Dump the fixed-schema button SQLite 3 log.
fruitjam-rtttl	Play a small RTTTL tune through the TLV320 PIO I2S tone path.
airliftctl	ESP32-C6 NINA firmware, WiFi, TCP, and MQTT diagnostics over SPI, including mqtt-pub and finite mqtt-sub.
mosquitto_pub	Tiny MQTT publisher with optional -u/-P; add --airlift to publish through the ESP32-C6.
mosquitto_sub	Tiny MQTT subscriber with optional -u/-P, -C, -W, and -v; add --airlift to subscribe through the ESP32-C6.
berry	Berry interpreter with -e, scripts, and REPL.
berry-run	Tiny wrapper that drops page cache before execing Berry for steadier multi-script runs.
/dev/neopixels	PIO-backed device for the five onboard NeoPixels.
BusyBox vi	On-target text editor.

/ is a read-only CramFS root. Use /tmp for temporary files and /mnt/sd for persistent data. The SD card is mounted as VFAT at /mnt/sd when present.

Host-side CDC smoke test

From macOS, run the automated smoke suite against the USB CDC Linux console:

./scripts/cdc-smoke-test.py

The default port is /dev/tty.usbmodem1101; override it with --port or FJ_CDC_PORT. The suite keeps one CDC shell open and checks Berry, board helpers, buttons, I2C, NeoPixels, loopback HTTP/Telnet/TFTP/FTP, and AirLift.

WiFi join and AirLift TCP tests run when credentials are supplied with either --ssid/--password, environment variables, or the ignored local env file:

cat > .fruitjam.env <<'EOF'
export FJ_WIFI_SSID=your-ssid
export FJ_WIFI_PASSWORD=your-passphrase
EOF
chmod 600 .fruitjam.env
./scripts/cdc-smoke-test.py

Use --audio to include the short RTTTL speaker test. Use --usb-keyboard with a boot-protocol HID keyboard plugged into the Fruit Jam host port to run kbd-find, the Berry USB keyboard helper, live kbd-auto-text/kbd-auto-events loops, and the kbd-auto-shell helper shell. Add --usb-keyboard-require-input when someone can press keys during the test and you want captured text/events plus a typed echo USBKBD_SMOKE shell command to be required. Use --skip-airlift or --skip-services to narrow the suite during bring-up.

For the USB-host keyboard milestone alone, the focused runner can use either the CDC shell or the AirLift telnet shell:

./scripts/usbhost-keyboard-smoke.py --transport cdc --port /dev/tty.usbmodem1101 --require-input
./scripts/usbhost-keyboard-smoke.py --transport telnet --telnet-host <board-ip> --require-input

The runner first checks that command markers round-trip through the selected board shell, then proves the current narrow boot-protocol keyboard path: kbd-find, the Berry helper, live text/events, and a typed command in kbd-auto-shell. The helper shell supports up/down history recall and tab completion for commands and paths.

Recent release-prep verification on June 12, 2026:

./scripts/cdc-smoke-test.py
./scripts/validate-fruitjam-examples.sh
./scripts/validate-fruitjam-image.sh buildroot-output-docker-images

The CDC suite is the broad regression entrypoint. Release-prep hardware checks also included direct AirLift HTTP, remote telnet, passive FTP list/upload/download and microphone-verified RTTTL/WAV audio on the flashed image.

Smoke test	Result	Evidence
USB CDC shell	PASS	fruitjam-cdc-ok over /dev/tty.usbmodem1101.
Kernel boot	PASS	Linux 6.15.0 no-MMU Buildroot console responded.
Tool inventory	PASS	airliftctl, berry, fruitjamctl, fruitjam-i2c, fruitjam-rtttl, fruitjam-services, fruitjam-buttons, fruitjam-usbhost, fruitjam-hidkeys, mosquitto_pub, mosquitto_sub, fruitjam-mem, free, fruitjam-uptime, uptime, fruitjam-du, du, fruitjam-ps, ps, fruitjam-pgrep, pgrep, pkill, wget, telnet, nc, tftp, and vi found in PATH.
Berry expression	PASS	berry -e 'print("berry-cdc-ok")' printed berry-cdc-ok.
Board status helper	PASS	fruitjamctl status reported LED, USB power, peripheral reset, and three buttons.
Button helper	PASS	fruitjam-buttons status reported button1/button2/button3 released.
I2C scan	PASS	fruitjam-i2c scan found device 0x18.
NeoPixel device	PASS	printf 'clear\nwrite\n' > /dev/neopixels completed.
AirLift probe	PASS	airliftctl probe reported spidev, firmware, MAC, status, and IP fields.
AirLift scan	PASS	airliftctl scan found visible networks.
AirLift WiFi join	PASS	Joined configured WiFi credentials and printed status/IP progress.
AirLift TCP GET	PASS	airliftctl tcp-get example.com / returned HTTP/1.1 200 OK.
Phase reboot	PASS	Test suite used fruitjamctl bootsel then picotool reboot -a -c riscv before service tests.
Service status	PASS	fruitjam-services status returned service/listener status without spawning large helpers.
HTTP CGI	PASS	AirLift HTTP returned mode":"airlift-direct" status JSON; loopback CGI is available through fruitjam-services core.
Telnet	PASS	AirLift telnet printed Fruit Jam telnet shell and echoed TELNET_SPEED_OK.
TFTP loopback	PASS	TFTP GET returned Fruit Jam TFTP area when the core loopback services were started.
FTP passive	PASS	Passive FTP over AirLift listed /mnt/sd, uploaded a file, and downloaded it with matching checksum.
RTTTL audio	PASS	scripts/fruitjam-audio-mic-test.py --serial-port /dev/cu.usbserial-P97cvdxp --mic-device 1 --loud --tone-hz 880 --tone-ms 2500 matched the 880 Hz tone from the speaker.

Working examples

These examples are meant to be run from the Fruit Jam console over USB CDC, UART, or telnet. They cover the features that have been brought up so far.

1. Check the default boot services and listeners:

   fruitjam-services status

   Expected services include the AirLift inbound worker and fruitjam-buttons daemon. External HTTP, telnet, and FTP are served by the AirLift worker after WiFi joins. The AirLift heartbeat line should stay below its 60-second stale restart window while the inbound worker is healthy.

2. Start the optional loopback service set for target-side HTTP/TFTP/FTP tests:

   fruitjam-services core

   This starts fruitjam-httpd, fruitjam-telnetd, fruitjam-ftpd, and TFTP on the local Linux network stack. It is useful for smoke tests from the console; the default boot path keeps these larger daemons out of memory until requested.

3. Fetch the SD-card placeholder page through the tiny HTTP client:

   wget -O - http://127.0.0.1/index.html

4. Run the CGI environment smoke test:

   wget -O - http://127.0.0.1/cgi-bin/env.cgi

   Expected output starts with Fruit Jam CGI OK.

5. Open the hardware playground:

   wget -O - http://127.0.0.1/playground
   wget -O - http://127.0.0.1/cgi-bin/fruitjam.cgi?action=status

   In a browser, visit http://<board-ip>/playground after AirLift joins WiFi. The page has status tiles, NeoPixel color pickers, button tests, RTTTL playback, WAV listing/playback, DVI helpers, USB-host status, Berry example controls, ADC reads, and I2C checks.

6. Drive NeoPixels through HTTP CGI using direct /dev/neopixels writes:

   wget -O - 'http://127.0.0.1/cgi-bin/fruitjam.cgi?action=neopixels&c0=%23ff0000&c1=%23ffaa00&c2=%2300ff66&c3=%230088ff&c4=%23aa44ff'

   Expected JSON includes "message":"neopixels updated". The web page no longer uses Berry for this fast hardware path; Berry is only invoked by the explicit Berry example runner.

7. Play the default RTTTL tune through the web API:

   wget -O - 'http://127.0.0.1/cgi-bin/fruitjam.cgi?action=rtttl'

8. Scan I2C and read ADC through the web API:

   wget -O - 'http://127.0.0.1/cgi-bin/fruitjam.cgi?action=i2c'
   wget -O - 'http://127.0.0.1/cgi-bin/fruitjam.cgi?action=adc&channel=temp'

9. Exercise the telnet shell over loopback:

   (echo 'echo TELNET_OK'; echo status; echo exit) | telnet 127.0.0.1 23

   Expected output includes Fruit Jam telnet shell and TELNET_OK. Interactive telnet sessions also support up/down history recall and tab completion for builtins, commands in /bin, /usr/bin, /sbin, and /usr/sbin, plus filesystem paths in command arguments.

10. Check the FTP control path:

(echo USER anonymous; echo PASS x; echo PWD; echo TYPE I; echo QUIT) | nc 127.0.0.1 21

Expected output includes 220 Fruit Jam FTP ready, 230 Login ok, and 221 Bye.

11. Fetch the TFTP README into /tmp:

tftp -g -r README.txt -l /tmp/tftp-readme.txt 127.0.0.1
cat /tmp/tftp-readme.txt

Expected output is Fruit Jam TFTP area.

12. Use nc as a tiny TCP server and client:

echo SERVERDATA > /tmp/nc-send.txt
: > /tmp/nc-recv.txt
nc -l -p 7008 < /tmp/nc-send.txt > /tmp/nc-recv.txt &
echo CLIENTDATA | nc 127.0.0.1 7008
cat /tmp/nc-recv.txt

Expected client output is SERVERDATA; the final cat should show CLIENTDATA.

13. Bridge a serial device over TCP:

/root/sh/serial-over-tcp.sh 7000 /dev/ttyGS0

In another shell, connect with nc 127.0.0.1 7000. With only the current userspace NINA helper there is no Linux wlan0, so remote access to this port needs a future Linux network interface or bridge.

14. Toggle the GPIO29 LED through sysfs:

echo 29 > /sys/class/gpio/export 2>/dev/null || true
echo out > /sys/class/gpio/gpio29/direction
echo 1 > /sys/class/gpio/gpio29/value
cat /sys/class/gpio/gpio29/value
echo 0 > /sys/class/gpio/gpio29/value

15. Toggle a female-header GPIO, for example GPIO6:

    echo 6 > /sys/class/gpio/export 2>/dev/null || true
    echo out > /sys/class/gpio/gpio6/direction
    echo 1 > /sys/class/gpio/gpio6/value
    cat /sys/class/gpio/gpio6/value
    echo 0 > /sys/class/gpio/gpio6/value

16. Inspect the three onboard buttons:

    fruitjam-buttons status

    GPIO0 is button 1, GPIO4 is button 2, and GPIO5 is button 3.

17. Inject a synthetic button event and inspect the SQLite log:

    echo 'button2 gpio4 test 123' > /run/fruitjam-buttons.fifo
    fruitjam-buttonlog dump /mnt/sd/fruitjam/buttons.db 5
    tail -n 5 /mnt/sd/fruitjam/buttons.log

18. Write, unmount, remount, and read the SD card:

    echo fruitjam_sd_audit > /mnt/sd/audit.txt
    umount /mnt/sd
    mount /mnt/sd
    cat /mnt/sd/audit.txt

19. Read ADC channels:

    fruitjam-adc read 0
    fruitjam-adc read temp

20. Scan or ping the I2C bus:

    fruitjam-i2c scan
    fruitjam-i2c ping 0x18
    berry-run /root/berry/11-i2c.be

    The TLV320DAC3100 control interface should acknowledge at 0x18.

21. Start the TLV320 clock path and run the RTTTL audio bring-up helper:

    echo start > /dev/fruitjam-audio
    fruitjam-rtttl --loud --tone 880 2500
    echo stop > /dev/fruitjam-audio

    Audible output was verified from the host with scripts/fruitjam-audio-mic-test.py. WAV playback exists through fruitjam-wavplay, but SD-card WAV files should be treated separately from the audio path when the kernel reports FAT read errors.

    To install and verify the generated sample WAV at /mnt/sd/wavs/fruitjam-scale.wav:

    scripts/fruitjam-audio-mic-test.py \
      --serial-port /dev/cu.usbserial-P97cvdxp \
      --install-sd-wav --run-wavplay --loud --rtttl scale

22. Run Berry expressions, scripts, and the REPL:

    berry -e 'print("hello fruit jam")'
    berry -e 'import math print(math.sqrt(81))'
    berry-run /root/berry/12-usbhost-keyboard.be
    berry-run /root/berry/13-airlift.be
    berry-run /root/berry/14-audio-wav.be
    berry-run /root/berry/15-board-control.be
    berry-run /root/berry/neopixels.be
    berry

    12-usbhost-keyboard.be prepares the kbd-find/live keyboard smoke commands for the PIO USB-host bridge, including the history/path-completion capable kbd-auto-shell helper. berry-run /root/berry/neopixels.be should drive the five onboard NeoPixels.

23. Inspect AirLift firmware, join WiFi, and perform an HTTP fetch through the ESP32-C6:

    airliftctl fw
    airliftctl join SSID PASSWORD
    airliftctl status
    airliftctl ip
    airliftctl tcp-get example.com /

    For automatic AirLift service join on the board, put credentials on the SD card instead of in the rootfs overlay:

    mkdir -p /mnt/sd/fruitjam
    chmod 700 /mnt/sd/fruitjam
    cat > /mnt/sd/fruitjam/wifi.conf <<'EOF'
    SSID=your-ssid
    PASSWORD=your-passphrase
    EOF
    chmod 600 /mnt/sd/fruitjam/wifi.conf

    Do not put real WiFi credentials in commits, image overlays, or public logs.

24. Publish and subscribe to MQTT through AirLift:

    mosquitto_sub --airlift -h 192.0.2.10 -p 1883 -t 'fruitjam/#' -C 1 -W 30 -v
    mosquitto_pub --airlift -h 192.0.2.10 -p 1883 -t fruitjam/test -m hello-from-fruitjam
    berry-run /root/berry/09-mqtt-publish.be
    berry-run /root/berry/10-mqtt-subscribe.be

    Replace the broker address with your own MQTT broker. Add -u USER -P PASSWORD when your broker requires authentication. The Berry examples use the fruitjam module MQTT helpers to build AirLift-aware mosquitto_pub and mosquitto_sub commands, then write environment-configurable scripts under /tmp.

    For an end-to-end publish and subscribe smoke test, run the focused host helper from the repo. It keeps the broker password out of command output:

    export FJ_MQTT_HOST=192.0.2.10
    export FJ_MQTT_USERNAME=your-user
    export FJ_MQTT_PASSWORD=your-password
    ./scripts/mqtt-smoke-test.py --transport cdc --port /dev/tty.usbmodem1101
    ./scripts/mqtt-smoke-test.py --transport telnet --telnet-host <board-ip>

    The smoke test proves both directions: target mosquitto_pub --airlift received by a host-side subscriber, and target mosquitto_sub --airlift receiving a host-side publish.

25. Route button events to MQTT through the SD-card config:

    mkdir -p /mnt/sd/fruitjam
    printf '%s\n' \
      MQTT_TRANSPORT=airlift \
      MQTT_HOST=192.0.2.10 \
      MQTT_PORT=1883 \
      MQTT_USER= \
      MQTT_PASSWORD= \
      MQTT_TOPIC=fruitjam/buttons \
      > /mnt/sd/fruitjam/buttons.conf
    fruitjam-services restart
    echo 'button2 gpio4 test 223' > /run/fruitjam-buttons.fifo

    fruitjam-buttons reads /etc/fruitjam-buttons.conf first and /mnt/sd/fruitjam/buttons.conf second at daemon startup, so restart services after changing the SD-card config.

26. Re-enter software BOOTSEL without pressing the physical button:

    fruitjamctl bootsel

    This disconnects the running system and should make the RP2350 BOOTSEL volume appear on the host.

    From the host, the repository helper can do the same recovery dance and then flash the current UF2 once picotool sees BOOTSEL. It tries the AirLift HTTP BOOTSEL action, the AirLift telnet shell, a DTR/RTS-disabled hardware UART shell if one is available, and CDC recovery. On macOS, CDC recovery tries both /dev/cu.usbmodem* and the matching /dev/tty.usbmodem* counterpart unless --no-tty-counterpart is passed:

    FJ_HTTP_HOST=<board-ip> FJ_TELNET_HOST=<board-ip> \
      ./scripts/fruitjam-recover-flash.py -v

    To force the hardware UART route, pass --uart-port /dev/cu.usbserial-P97cvdxp or set FJ_UART_PORT=/dev/cu.usbserial-P97cvdxp.

Build and flash:

git submodule update --init
make -C buildroot BR2_EXTERNAL=$PWD adafruit_fruit_jam_rp2350_defconfig
make -C buildroot
picotool load -fu buildroot/output/images/flash-image.uf2

If picotool was not available during the Buildroot post-image step, generate the UF2 manually:

picotool uf2 convert buildroot/output/images/flash-image.bin \
  buildroot/output/images/flash-image.uf2 --family rp2350-riscv

See board/adafruit/adafruit_fruit_jam_rp2350/README.md for board assumptions, serial wiring, expected boot log, and limitations. See docs/pinmap-fruitjam.md, docs/risks.md, and docs/milestones.md for follow-on work.

Raspberry Pi Pico 2 / SparkFun Pro Micro RP2350

The original target is still available:

git submodule update --init
make -C buildroot BR2_EXTERNAL=$PWD raspberrypi-pico2_defconfig
make -C buildroot
picotool load -fu buildroot/output/images/flash-image.uf2

Notes on RP2350 atomics

RP2350 reports a Store/AMO access fault if RISC-V AMO/exclusive operations target a region that does not support atomics. External PSRAM is not normal cache-coherent RAM, but this port places the kernel in PSRAM. The existing patch stack includes RP2350 workarounds for Linux atomics; do not remove those patches without a replacement and a hardware test plan.