SiloOS SFWU Protocol Skill

When to Use

• Implementing new TopBrewer commands
• Debugging packet parsing issues
• Verifying CRC32 checksum calculations
• Adding new response parsers

Prerequisites

• Understanding of binary protocols and hex encoding
• Familiarity with BLE GATT characteristics
• Knowledge of the SFWU packet structure

Protocol Reference

Packet Format

Byte:   0      1-2        3-4       5-6       7..N-4    N-3..N
Field:  HEADER LENGTH     COMMAND   ADDRESS   PAYLOAD   CRC32
Size:   1      2          2         2         variable  4

• HEADER: Always 0x01
• LENGTH: Total packet length (big-endian uint16)
• COMMAND: Command code (big-endian uint16)
• ADDRESS: Target address (big-endian uint16)
• PAYLOAD: Command-specific data
• CRC32: CRC32-CCITT over all preceding bytes

Key Commands (from constants.ts)

Command	Code	Description
RESET	0x00C0	Reset machine state
GET_MENU	0x00C1	Request drink menu
GET_MENU_DETAILS	0x00C2	Request menu item details
ORDER	0x00C3	Place a drink order
GET_BREW_STATUS	0x00C4	Poll brewing progress
GET_TEMPERATURES	0x00C5	Request temperature readings

CRC32-CCITT Implementation

// From CRC32.ts — DO NOT modify this implementation
Polynomial: 0xEDB88320 (reflected)
Initial:    0xFFFFFFFF
Final XOR:  0xFFFFFFFF

Procedure

Adding a New Command

1. Define the command code in sfwu/constants.ts
2. Create a builder in sfwu/commands/
3. Use SFWU.buildPacket(command, address, payload) to construct
4. CRC32 is calculated automatically

Adding a New Parser

1. Create parser in sfwu/parsers/
2. Implement parse(data: Uint8Array): YourEntity
3. Add entity interface in entities/
4. Register in ResponseFactory.ts

Testing Packets

Use the existing test vectors in sfwu/tests.ts:

const packet = SFWU.buildPacket(0x00C1, 0x0000, new Uint8Array([]));

Expected Outcomes

• Packets build correctly with valid CRC32
• Responses parse into correct TypeScript entities
• No data corruption across BLE chunked writes