CRC protocol new mode to drop pkt & continue

[jmthomas]

The CRC protocol currently has 2 modes: DISCONNECT and ERROR. However on ERROR it keeps the data and returns it. We need a new mode (DROP?) that prints the error but drops the packet and doesn't return it back to the interface.

[crawlchat]

Great, I have a full picture of both implementations. Here's a thorough breakdown of what needs to change and where:

---

📋 Summary of Required Changes

The DROP mode should:

1. Log the CRC error (same as ERROR)
2. Return STOP to silently drop the packet — not pass it back to the interface

This is distinct from:

• ERROR → logs + returns data anyway
• DISCONNECT → logs + disconnects the interface

---

Changes Needed

Both files follow the same pattern. Here's what needs to be updated:

1. Ruby — openc3/lib/openc3/interfaces/protocols/crc_protocol.rb

# Line 26-27 — Add the new constant
ERROR = "ERROR"
DISCONNECT = "DISCONNECT"
DROP = "DROP"  # ← ADD THIS

# Line 58-63 — Add DROP to the validation
case bad_strategy
when ERROR, DISCONNECT, DROP   # ← ADD DROP
  @bad_strategy = bad_strategy
else
  raise "Invalid bad CRC strategy of #{bad_strategy}. Must be ERROR, DISCONNECT, or DROP."
end

# Line 157-162 — Add DROP handling in read_data
if calculated_crc != crc
  Logger.error "#{@interface ? @interface.name : ""}: Invalid CRC detected! Calculated 0x#{calculated_crc.to_s(16).upcase} vs found 0x#{crc.to_s(16).upcase}."
  if @bad_strategy == DISCONNECT
    return :DISCONNECT
  elsif @bad_strategy == DROP   # ← ADD THIS BLOCK
    return :STOP
  end
end

---

2. Python — openc3/python/openc3/interfaces/protocols/crc_protocol.py

# Line 22-23 — Add the new constant
ERROR = "ERROR"
DISCONNECT = "DISCONNECT"
DROP = "DROP"  # ← ADD THIS

# Line 56-60 — Add DROP to the match validation
match bad_strategy:
    case CrcProtocol.ERROR | CrcProtocol.DISCONNECT | CrcProtocol.DROP:  # ← ADD DROP
        self.bad_strategy = bad_strategy
    case _:
        raise ValueError(f"Invalid bad CRC strategy of {bad_strategy}. Must be ERROR, DISCONNECT, or DROP.")

# Line 152-158 — Add DROP handling in read_data
if calculated_crc != crc:
    interface = ""
    if self.interface:
        interface = self.interface.name
    Logger.error(f"{interface}: Invalid CRC detected! Calculated {hex(calculated_crc)} vs found {hex(crc)}.")
    if self.bad_strategy == CrcProtocol.DISCONNECT:
        return ("DISCONNECT", extra)
    elif self.bad_strategy == CrcProtocol.DROP:  # ← ADD THIS BLOCK
        return ("STOP", extra)

---

3. Don't forget the docs!

The Bad Strategy parameter description in the docs should be updated:

ERROR = Just log the error, DISCONNECT = Disconnect interface, DROP = Log the error and drop the packet

---

A few questions for the team before merging:

1. Should DROP also respect strip_crc? Currently, STOP would be returned before the strip logic runs — which seems correct since we're dropping the packet entirely.
2. Should tests be added for the new DROP mode in the existing test files (test_crc_protocol.rb / test_crc.py)?
3. Should the docs page default value description for Bad Strategy remain "ERROR" or be updated to reflect all three options?