OTA — Over-the-Air Update

PrintDrop uses a dual-OTA layout so a failed flash does not brick the stick. The single-app partitions_printdrop.csv cannot safely update itself.

Partitions

partitions_printdrop_ota.csv:1 (used by env:printdrop platformio.ini:23):

nvs      0x9000  20 KB
otadata  0xE000   8 KB
app0     0x10000 1 344 KB  ota_0
app1     0x160000 1 344 KB ota_1
spiffs   0x2B0000 1 280 KB LittleFS
coredump 0x3F0000   64 KB

Each slot holds ~1 344 KB; current firmware is ~980 KB pio run -e printdrop so it fits with headroom. app0 is ota_0, app1 ota_1; otadata tracks the boot slot. printdrop_spi keeps the old single-app table for bring-up without OTA.

Disable OTA on tight builds: -D PRINTDROP_ENABLE_OTA=0 config.h:135.

HTTP OTA

POST /api/ota (requires auth) streams a raw .bin to Update (src/printdrop/ota.cpp:44, web.cpp:400).

Web UI Settings → Firmware: choose a .bin (built via pio run -e printdrop -t build → .pio/build/printdrop/firmware.bin). The UI posts as multipart/form-data to /api/ota and shows progress; success reboots.

curl:

curl -u admin:printdrop -F "file=@.pio/build/printdrop/firmware.bin" http://printdrop.local/api/ota

Serial alternative is still pio run -e printdrop -t upload over COM11/COM5 with the BOOT hatch docs/flashing.md.

SD-card OTA

Copy to the SD root (FAT32):

firmware.bin              # same file as above
firmware.json             # {"version":"0.2.0","notes":"fix xyz"}

On boot and on each GET /api/status / GET /api/ota/status, ota::checkSD() (ota.cpp:34) compares firmware.json:version against PRINTDROP_VERSION. If newer, the UI shows SD update available: 0.2.0 with Update from SD. POST /api/ota/sd streams the file via Update and reboots. The web UI also polls api/ota/status.

Version is a plain string compare; use semver so 0.2.0 ≠ 0.1.0.

Safety

Update is guarded by storage::Guard and hostWrote logic; the card is remounted after.
Update.begin(total) validates size against the OTA slot before writing; power loss during flash leaves the other slot bootable.
Factory reset (button 5 s, serial factory-reset, or clear-auth + Wi-Fi forget) does not touch OTA slots.