# Development

Two modes exist:

- simulator development
- device firmware development


# Simulator Development Mode

Used for rapid iteration.

Typical loop:


edit code
run simulator
inspect UI behavior
repeat


Use this mode for:

- layout development
- UI interaction
- application logic

Simulator behavior may differ from hardware.

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# Device Firmware Mode

Used when testing on the PineTime.

Typical loop:


cargo build
generate firmware image
package OTA update
upload to watch
reboot device
verify behavior


Testing on hardware is necessary for:

- BLE
- memory limits
- timing behavior
- display performance

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# OTA Packaging

The intended artifact chain is:


cargo build
→ firmware ELF
→ binary image
→ OTA zip package
→ upload via companion app


Exact tooling may evolve as the project stabilizes.

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# OTA Verification

The PineTime bootloader uses a verification model.

Steps:

1. firmware installed to secondary slot
2. bootloader boots new firmware once
3. firmware runs in **unconfirmed state**
4. firmware must confirm itself
5. bootloader marks it permanent

If confirmation does not happen:


reboot → previous firmware restored


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# Safety Guidelines

Bootloader safety:

- never overwrite bootloader memory
- treat bootloader as protected space

Firmware safety:

- avoid breaking both firmware slots
- always test new firmware as unconfirmed

Development discipline:

- simulator success is not sufficient
- always validate hardware behavior