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Writing a SANA-II Network Device Driver

Overview

A SANA-II driver is an Amiga device that implements the SANA-II specification. It provides the bridge between a TCP/IP stack (bsdsocket.library) and network hardware. This guide covers writing a complete SANA-II driver from scratch.

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Architecture

TCP/IP Stack (AmiTCP/Roadshow)
    ↓ OpenDevice("mynet.device", 0, ios2req, 0)
    ↓ CMD_READ / CMD_WRITE / S2_DEVICEQUERY / ...
SANA-II Device Driver (mynet.device)
    ↓ Hardware register access / DMA
Network Hardware (Ethernet NIC / FPGA bridge)

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Required Commands

Every SANA-II driver must implement these commands:

Command	Code	Description
CMD_READ	2	Read a packet (async — queue and reply when packet arrives)
CMD_WRITE	3	Send a packet
CMD_FLUSH	8	Abort all pending I/O
S2_DEVICEQUERY	9	Report hardware capabilities
S2_GETSTATIONADDRESS	10	Return MAC address
S2_CONFIGINTERFACE	11	Set MAC address and bring up
S2_ONLINE	14	Bring interface online
S2_OFFLINE	15	Take interface offline
S2_ADDMULTICASTADDRESS	16	Join multicast group
S2_DELMULTICASTADDRESS	17	Leave multicast group
S2_GETGLOBALSTATS	21	Return packet statistics
S2_ONEVENT	22	Notify on event (link up/down)
S2_READORPHAN	23	Read unmatched packet types

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struct IOSana2Req

/* devices/sana2.h — NDK39/SANA-II Spec */
struct IOSana2Req {
    struct IORequest ios2_Req;
    ULONG  ios2_WireError;       /* wire-level error code */
    ULONG  ios2_PacketType;      /* Ethernet type (e.g. 0x0800 = IPv4) */
    UBYTE  ios2_SrcAddr[SANA2_MAX_ADDR_BYTES];  /* source MAC */
    UBYTE  ios2_DstAddr[SANA2_MAX_ADDR_BYTES];  /* destination MAC */
    ULONG  ios2_DataLength;      /* data length */
    APTR   ios2_Data;            /* packet data (via buffer management) */
    APTR   ios2_StatData;        /* statistics data pointer */
    APTR   ios2_BufferManagement; /* buffer mgmt hooks from stack */
};

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Buffer Management Hooks

The TCP/IP stack provides buffer copy functions via tags at OpenDevice time. Your driver must use these — never copy data directly:

/* In your DevOpen: */
typedef BOOL (*CopyToBuff)(APTR to, APTR from, ULONG len);
typedef BOOL (*CopyFromBuff)(APTR to, APTR from, ULONG len);

struct BufferManagement {
    CopyToBuff   bm_CopyToBuff;
    CopyFromBuff bm_CopyFromBuff;
};

/* Parse tags from ios2req->ios2_BufferManagement: */
struct TagItem *tags = (struct TagItem *)ios2req->ios2_BufferManagement;
struct BufferManagement *bm = AllocMem(sizeof(*bm), MEMF_PUBLIC);
bm->bm_CopyToBuff   = (CopyToBuff)GetTagData(S2_CopyToBuff, 0, tags);
bm->bm_CopyFromBuff = (CopyFromBuff)GetTagData(S2_CopyFromBuff, 0, tags);
ios2req->ios2_BufferManagement = bm;

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Implementing CMD_READ (Receive Path)

void CmdRead(struct IOSana2Req *ios2, struct MyDevBase *base)
{
    struct MyUnit *unit = (struct MyUnit *)ios2->ios2_Req.io_Unit;

    /* CMD_READ is ALWAYS async — queue the request */
    ios2->ios2_Req.io_Flags &= ~IOF_QUICK;

    Disable();
    /* Queue by packet type for fast dispatch on interrupt: */
    struct ReadQueue *rq = FindReadQueue(unit, ios2->ios2_PacketType);
    if (!rq) {
        rq = CreateReadQueue(unit, ios2->ios2_PacketType);
    }
    AddTail(&rq->rq_List, &ios2->ios2_Req.io_Message.mn_Node);
    Enable();

    /* Do NOT ReplyMsg — will be replied when a packet arrives */
}

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Implementing CMD_WRITE (Transmit Path)

void CmdWrite(struct IOSana2Req *ios2, struct MyDevBase *base)
{
    struct MyUnit *unit = (struct MyUnit *)ios2->ios2_Req.io_Unit;
    struct BufferManagement *bm = ios2->ios2_BufferManagement;

    UBYTE txbuf[1536];  /* max Ethernet frame */
    ULONG len = ios2->ios2_DataLength;

    /* Build Ethernet header: */
    CopyMem(ios2->ios2_DstAddr, &txbuf[0], 6);   /* dest MAC */
    CopyMem(unit->mu_StationAddr, &txbuf[6], 6);  /* src MAC */
    txbuf[12] = (ios2->ios2_PacketType >> 8) & 0xFF;
    txbuf[13] = ios2->ios2_PacketType & 0xFF;

    /* Copy payload from stack's buffer: */
    bm->bm_CopyFromBuff(&txbuf[14], ios2->ios2_Data, len);

    /* Send to hardware: */
    HW_Transmit(unit, txbuf, len + 14);

    ios2->ios2_Req.io_Error = 0;
    TermIO(ios2);
}

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Interrupt Handler (Packet Arrival)

/* Called when hardware signals packet received: */
LONG __saveds RxInterrupt(struct MyDevBase *base __asm("a1"))
{
    struct MyUnit *unit = base->md_Units[0];
    UBYTE rxbuf[1536];
    ULONG len;

    while (HW_HasPacket(unit)) {
        len = HW_ReceivePacket(unit, rxbuf, sizeof(rxbuf));

        UWORD ptype = (rxbuf[12] << 8) | rxbuf[13];

        /* Find a pending CMD_READ for this packet type: */
        struct ReadQueue *rq = FindReadQueue(unit, ptype);
        if (rq && !IsListEmpty(&rq->rq_List)) {
            struct IOSana2Req *ios2 =
                (struct IOSana2Req *)RemHead(&rq->rq_List);

            struct BufferManagement *bm = ios2->ios2_BufferManagement;
            bm->bm_CopyToBuff(ios2->ios2_Data, &rxbuf[14], len - 14);

            CopyMem(&rxbuf[6], ios2->ios2_SrcAddr, 6);
            ios2->ios2_DataLength = len - 14;
            ios2->ios2_Req.io_Error = 0;

            ReplyMsg(&ios2->ios2_Req.io_Message);
        } else {
            unit->mu_Stats.DroppedPackets++;
        }
    }
    return 0;
}

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S2_DEVICEQUERY Response

void CmdDeviceQuery(struct IOSana2Req *ios2, struct MyDevBase *base)
{
    struct Sana2DeviceQuery *query = ios2->ios2_StatData;

    query->DevQueryFormat = 0;
    query->DeviceLevel    = 0;
    query->AddrFieldSize  = 48;    /* 48-bit MAC */
    query->MTU            = 1500;  /* Ethernet MTU */
    query->BPS            = 100000000;  /* 100 Mbps */
    query->HardwareType   = S2WireType_Ethernet;

    ios2->ios2_Req.io_Error = 0;
    TermIO(ios2);
}

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Building

CFLAGS = -noixemul -m68000 -Os -fomit-frame-pointer
mynet.device: mynet.o
    $(CC) $(CFLAGS) -nostartfiles -o $@ $^

Install to DEVS:Networks/mynet.device.

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References

• SANA-II Network Device Driver Specification v2 (Commodore)
• NDK39: devices/sana2.h
• Example drivers: a2065.device source, plipbox driver