Fire Pong/Interfaces/Puffer Control

Purpose

This interface defines how the main game control unit signals other parts of the system to set off the various puffers in the system.

Requirements

• All puffers on a serial bus, each with ID mask (see below)
• Serial bus params TBD, but probably slowish with error correction if possible because interference from sparkers:
  • RS232 because Mouse has a bunch of MAX3232 converters
  • parity if possible
• Only control box writes to bus
• Only well-formed event packets are processed by puffers to prevent accidental firings due to corrupted packets
  • Packet starts with two-byte "magic"
  • Packet ends with one-byte CRC8 of the rest of the packet (excluding magic)
• Events are processed immediately by clients
• Client addresses are 2**n values - there may be 32 clients on the bus at a time
• Multiple clients can be addressed in a single packet

IDs

• Each puffer has an ID mask, which is:
  • a 32-bit unsigned integer (uint32_t from stdint.h)
  • little endian
  • mask with a single bit set, i.e. 0x00000001, 0x00000002, 0x00000004, 0x00000008, ..., 0x80000000
• Requests include an ID set, which is:
  • a 32-bit unsigned integer (uint32_t from stdint.h)
  • little endian
  • mask with one or more bits set e.g. 0x00003001, corresponding to ID masks 0x00000001, 0x00001000, and 0x00002000,

Event Types

• Enumerated event type:
  • 0: STOP (requires manual reset)
  • 1: Spark/ignite only
  • 2: Puff sequence
  • other: undefined (do nothing)
• 8-bit unsigned integer (uint8_t from stdint.h)
• little endian

Durations

• A time in milliseconds for a puffer solenoid valve to be open for
• Typically 100 or 150 for small puffers
• Between 100 and 2000ms for large puffers (?)
• 16-bit unsigned integer (uint16_t from stdint.h)
• little endian

Checksum

Because of the sparkers, we're operating in a noisy environment, so we need error detection so that we don't end up running too many sparkers at once (and causing too much current draw).

• A checksum value is a 8-bit unsigned integer which is set the the CRC8 checksum of the other seven bytes of data in order, as calculated by the CRC polynomial X^8 + X^5 + X^4 + X^0.
• Implementation from here

Events

• Events are sent in real time and processed immediately by all puffer controllers on the bus
• An event consists of an ID set, and Event Type, a Duration and a check byte
• No acknowledgement is required - this is a broadcast only protocol

Example C code

   #include <stdint.h>
   
   typedef struct PufferEvent {
       uint32_t id_set;
       uint8_t  type;
       uint16_t duration;
       uint8_t checksum;
   } t_PufferEvent;