PROFINET¶

Status: Planned

This module is not yet implemented. The design below represents the target architecture.

Overview¶

PROFINET is the industrial Ethernet standard from PROFIBUS International (PI). It provides three communication channels: non-real-time (TCP/UDP), real-time (RT, cyclic at Layer 2), and isochronous real-time (IRT, hardware-synchronized with sub-microsecond jitter).

Architecture¶

┌──────────────────────────────────────────────────────────────────────┐
│  PROFINET Communication Stack:                                        │
│                                                                       │
│  ┌───────────────────────────────────────────────────────────────┐   │
│  │  Application (PLC program, drive control, I/O)                 │   │
│  ├───────────────┬───────────────────┬───────────────────────────┤   │
│  │   NRT (TCP/IP)│    RT (Cyclic)    │     IRT (Isochronous)    │   │
│  │  - Parameter  │  - Process data   │  - Motion control         │   │
│  │  - Diagnostics│  - 1-10 ms cycle  │  - < 1 ms cycle          │   │
│  │  - Config     │  - VLAN priority  │  - Hardware forwarding    │   │
│  ├───────────────┼───────────────────┼───────────────────────────┤   │
│  │   UDP/TCP     │  Ethernet L2      │  Ethernet L2 (scheduled) │   │
│  │   (standard)  │  (EtherType       │  (Time-triggered)        │   │
│  │               │   0x8892)         │                           │   │
│  └───────────────┴───────────────────┴───────────────────────────┘   │
└──────────────────────────────────────────────────────────────────────┘

PROFINET Frame Format (RT)¶

┌──────────────────────────────────────────────────────────────────────┐
│ Dst MAC │ Src MAC │ VLAN Tag │ EtherType │  Frame ID  │   Data    │ │
│ (6B)    │ (6B)    │ (4B opt) │  0x8892   │  (2 bytes) │(variable) │ │
└──────────────────────────────────────────────────────────────────────┘

Frame ID Ranges:
  0x0100-0x7FFF: RT (cyclic process data)
  0x8000-0xBFFF: RT (acyclic, alarms)
  0xC000-0xFBFF: IRT (isochronous, time-critical)
  0xFC00-0xFCFF: RTC3 (high-performance)
  0xFE00-0xFEFF: DCP (Discovery and Configuration Protocol)

Communication Classes¶

Class	Cycle Time	Jitter	Use Case
NRT	N/A	N/A	Configuration, diagnostics
RT (Class 1)	10 ms	±1 ms	Standard I/O
RT (Class 2)	1-10 ms	±100 µs	Fast I/O
IRT (Class 3)	250 µs–1 ms	< 1 µs	Motion, servo

Planned API¶

typedef struct {
    raw_socket_t raw;              /* Underlying raw socket */
    uint16_t     frame_id;         /* Cyclic frame ID */
    uint32_t     cycle_time_us;    /* Send interval */
    uint16_t     station_name_len;
    char         station_name[240]; /* PROFINET station name */
    uint8_t      mac_addr[6];
} pn_controller_t;

typedef struct {
    uint16_t slot;
    uint16_t subslot;
    uint16_t data_offset;
    uint16_t data_length;
} pn_io_module_t;

/* Controller lifecycle */
int pn_controller_init(pn_controller_t *ctrl, const char *if_name);
int pn_discover_devices(pn_controller_t *ctrl);  /* DCP protocol */
int pn_connect(pn_controller_t *ctrl, const char *station_name);
int pn_controller_close(pn_controller_t *ctrl);

/* Cyclic I/O */
int pn_io_read(pn_controller_t *ctrl, pn_io_module_t *module,
               void *data, size_t len);
int pn_io_write(pn_controller_t *ctrl, pn_io_module_t *module,
                const void *data, size_t len);

/* Acyclic (parameter access) */
int pn_read_record(pn_controller_t *ctrl, uint16_t slot, uint16_t subslot,
                   uint16_t index, void *data, size_t *len);
int pn_write_record(pn_controller_t *ctrl, uint16_t slot, uint16_t subslot,
                    uint16_t index, const void *data, size_t len);

Device Discovery (DCP)¶

┌─────────────────────────────────────────────────────────────────┐
│  DCP (Discovery and Configuration Protocol):                     │
│                                                                  │
│  Controller                              Device                  │
│      │                                      │                    │
│      │── DCP Identify (multicast) ─────────►│                    │
│      │                                      │                    │
│      │◄── DCP Identify Response ────────────│                    │
│      │    (station name, IP, MAC)           │                    │
│      │                                      │                    │
│      │── DCP Set (IP address) ─────────────►│                    │
│      │                                      │                    │
│      │── DCP Set (Station Name) ───────────►│                    │
│      │                                      │                    │
└─────────────────────────────────────────────────────────────────┘

Performance Targets¶

Metric	Target	Notes
RT cycle time	1 ms	Class 2
IRT cycle time	250 µs	Class 3 (hardware forwarding)
DCP discovery	< 100 ms	Multicast scan
Failover (MRP)	< 200 ms	Media Redundancy Protocol

Implementation Roadmap¶

PROFINET frame construction (EtherType 0x8892)
DCP Identify multicast (device discovery)
DCP Set (IP and station name assignment)
Context Manager (connection setup, AR establishment)
Cyclic RT provider/consumer
IOPS/IOCS status handling
Alarm and diagnostic channels
Integration with epoll_reactor (timer-driven RT cycles)
MRP (Media Redundancy Protocol) for ring topology