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Configuration Notes for CanTp

CanTp implements ISO 15765-2 segmented transfer over CAN. It connects downward to CanIf and upward to PduR. The configuration is consumed by CanTp.py; the example in this document is app/app/config/CanTp/CanTp.json and the generated code is CanTp_Cfg.c.

1. Channel-based design

Each entry in channels creates one logical CanTp channel. A channel always owns exactly one RxPdu and one TxPdu - the generator derives their CanIf names from the channel name as ${name}_RX and ${name}_TX.

{
  "class": "CanTp",
  "channels": [
    { "name": "P2P" },
    { "name": "P2A", "ComType": "FUNCTIONAL" },
    { "name": "P2A_FW", "ComType": "FUNCTIONAL" }
  ],
  "backup-channels": [
    { "name": "FW_CAN0_SECOC_MSG0" }
  ]
}

channels - physical and functional diagnostic channels. ComType is PHYSICAL (default) or FUNCTIONAL;
backup-channels - channels used as a SecOC fallback path. A backup channel is instantiated but is not routed until SecOC switches to it.

The corresponding CanIf PDUs must exist in CanIf.json with matching names and the up field set to CanTp:

"RxPdus": [
  { "name": "P2P_RX", "id": "0x731", "hoh": 0, "up": "CanTp" },
  { "name": "P2A_RX", "id": "0x7DF", "hoh": 0, "up": "CanTp" }
],
"TxPdus": [
  { "name": "P2P_TX", "id": "0x732", "hoh": 0, "up": "CanTp" },
  { "name": "P2A_TX", "id": "0x732", "hoh": 0, "up": "CanTp" }
]

2. Channel parameters

Every field except name is optional and falls back to a compiled default:

Field	Default	Description
`name`	-	Channel name; derives the CanIf `${name}_RX` / `${name}_TX` PDU names and the PduR routing IDs
`ComType`	`PHYSICAL`	`PHYSICAL` for 1-to-1 physical addressing or `FUNCTIONAL` for functional requests (CAN ID 0x7DF)
`N_As`	0	Time for transmitting a CAN frame (any N-PDU) on the sender side
`N_Bs`	0	Time until the next flow control N-PDU is received (ISO 15765-2)
`N_Cr`	0	Time until the next consecutive frame N-PDU is received (ISO 15765-2)
`STmin`	0	Minimum separation time between two consecutive frames
`BS`	0	Block size used in outgoing flow control frames
`WftMax`	8	Number of consecutive wait (FC-WAIT) flow control frames allowed; must not be 0xFF
`LL_DL`	`CANTP_LL_DL` (8)	Lower-layer data length: 8 for classic CAN, 64 for CAN FD
`padding`	`0x55`	Padding byte used when padding is enabled
`N_TA`	0	Network target address, required only for extended addressing

A top-level STMinAdjust lets the generated code add a constant correction to the negotiated STmin. In the host simulator, the environment variable LL_DL overrides LL_DL of every channel at process start, which makes it possible to switch the same build between classic CAN and CAN FD without regenerating.

The generated channel struct is:

typedef struct {
  CanTp_AddressingFormatType AddressingFormat;
  PduIdType CanIfTxPduId;
  PduIdType PduR_RxPduId;
  PduIdType PduR_TxPduId;
  uint16_t N_As;
  uint16_t N_Bs;
  uint16_t N_Cr;
  uint8_t STmin;
  uint8_t BS;
  uint8_t N_TA;              /* only used with CANTP_EXTENDED addressing */
  uint8_t CanTpRxWftMax;     /* cannot be 0xFF */
  uint8_t LL_DL;             /* 8 for CAN, 64 for CAN FD */
  uint8_t padding;
  uint8_t *data;             /* transmit buffer for segmented frames */
} CanTp_ChannelConfigType;

3. Notes

The JSON schema exposes the common parameters. For advanced tuning (addressing format, custom buffer sizes) edit the generated CanTp_Cfg.c directly.
CanTp never appears in a DBC file; its frames are always declared explicitly in CanIf.json.
Routing between CanTp and the upper layer (Dcm, DoIP, LinTp or another CanTp for gateways) is generated by the PduR generator, see the PduR document.

4. Generator

Configuration is processed by: CanTp.py, which emits GEN/CanTp_Cfg.c and GEN/CanTp_Cfg.h next to the JSON file.

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