# Oracle — the hand-written TinySafeBoot assembly

`tsb-fixedbaud.asm` is the reference implementation this port is measured
against: the **native-UART, fixed-baud** TinySafeBoot bootloader, hand-written
in AVR assembly. It is the size-and-feature bar for the port's `tsb_asm` tier.

- **Source**: <https://github.com/seedrobotics/tinysafeboot>
  (`firmware_ASM/latest_stable_release/20200727-fixedbaud/main.asm`), the Seed
  Robotics fixed-baud fork of Julien Thomas' TinySafeBoot.
- **License**: GPLv3 (see the header in the file). It is vendored here **only as
  a reference oracle** — it is not compiled, linked, or distributed as part of
  the MIT-licensed port. Mere aggregation.

## Why this variant

The user chose the fixed-baud, hardware-UART variant deliberately: it is the one
whose feature set the port must match. It fits the **complete** TSB feature set
into the 512-byte ATmega boot section:

| Feature | Oracle routine |
|---|---|
| Watchdog-reset bail straight to the app | `RESET` (WDRF check) |
| One-wire half-duplex (RX/TX shorted): RXEN/TXEN toggled per direction, TX turnaround guard | `SetRX` / `SetTX` / `TransmitByte` |
| Activation timeout read from the config page, with a lockout-proof minimum | `WRX1To` (uses `utimeoutH`) |
| 3×`@` activation knock | `ActCharRcvd` |
| Password gate; wrong byte hangs (still draining the UART) | `CheckPassword` |
| Emergency erase on password `\0` + double-confirm — wipes flash, EEPROM and the config page | `EmergencyErase` |
| Device-info block (16 bytes) | `SendDeviceInfo` / `DEVICEINFO` |
| App-flash read/write (`f`/`F`), EEPROM read/write (`e`/`E`), config read/write (`c`/`C`) | `CheckCommands` |

## Assembled size (the bar)

Assembled for the ATmega328P with `avra`:

```
avra -I /usr/share/avra tsb-fixedbaud.asm   # after uncommenting .include "m328Pdef.inc"
#   Code : 250 words (500 bytes)  — the whole loader, all features, in the 512 B section
```

**500 bytes with every feature** — the proof that ≤512 B and full feature parity
are simultaneously reachable. The port's `tsb_asm` tier matches this bar; `tsb_pure`
and `tsb_tricks` implement the same protocol at larger sizes in the 1 KB section,
trading bytes for readability.

The oracle targets 20 MHz / 33333 baud; the port targets 16 MHz / 115200 baud
(what the simavr protocol test drives). Baud and geometry differ, code size and
feature set do not.