gsplus/src/atbridge/llap.c

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2016-02-08 05:01:25 +00:00
/*
GSPLUS - Advanced Apple IIGS Emulator Environment
Based on the KEGS emulator written by Kent Dickey
See COPYRIGHT.txt for Copyright information
See COPYING.txt for license (GPL v2)
2016-02-08 05:01:25 +00:00
*/
/** This module implements the LLAP port of the bridge. **/
#include <stdbool.h>
#include "../defc.h"
#include "atbridge.h"
#include "port.h"
#include "llap.h"
typedef enum {
LLAP_DDP_SHORT = 0x01,
LLAP_DDP_LONG = 0x02,
LLAP_ENQ = 0x81,
LLAP_ACK = 0x82,
LLAP_RTS = 0x84,
LLAP_CTS = 0x85
} LLAP_TYPES;
const unsigned int LLAP_PACKET_MAX = 603 /* bytes */;
const unsigned int LLAP_PACKET_MIN = 3 /* bytes */;
const double LLAP_IDG = 400 /* microseconds */;
const double LLAP_IFG = 200 /* microseconds */;
const double GAP_TOLERANCE = 4.0;
static struct packet_port_t llap_port;
typedef enum {
DIALOG_READY,
DIALOG_GOT_CTS,
DIALOG_WAIT_IDG
} DIALOG_STATE;
static DIALOG_STATE dialog_state;
static double dialog_end_dcycs;
static double last_frame_dcycs;
void llap_init()
{
dialog_state = DIALOG_READY;
last_frame_dcycs = 0;
port_init(&llap_port);
}
void llap_shutdown()
{
port_shutdown(&llap_port);
}
/** Queue one data packet out from the bridge's LLAP port and into the guest. **/
void llap_enqueue_out(struct packet_t* packet)
{
// Generate the RTS.
struct packet_t* rts = (struct packet_t*)malloc(sizeof(struct packet_t));
rts->source.network = packet->source.network;
rts->source.node = packet->source.node;
rts->dest.network = packet->dest.network;
rts->dest.node = packet->dest.node;
rts->size = 0;
rts->data = 0;
rts->type = LLAP_RTS;
enqueue_packet(&llap_port.out, rts);
// Enqueue the data.
enqueue_packet(&llap_port.out, packet);
}
struct packet_t* llap_dequeue_in()
{
return dequeue(&llap_port.in);
}
static void llap_dump_packet(size_t size, byte data[])
{
if (size < LLAP_PACKET_MIN)
atbridge_printf("LLAP short packet.\n");
else if (size > LLAP_PACKET_MAX)
atbridge_printf("LLAP long packet.\n");
else
{
at_node_t dest = data[0];
at_node_t source = data[1];
LLAP_TYPES type = (LLAP_TYPES)(data[2]);
const char* typeName = 0;
switch (type)
{
case LLAP_DDP_SHORT:
typeName = "DDP (short)";
break;
case LLAP_DDP_LONG:
typeName = "DDP (long)";
break;
case LLAP_ENQ:
typeName = "lapENQ";
break;
case LLAP_ACK:
typeName = "lapACK";
break;
case LLAP_RTS:
typeName = "lapRTS";
break;
case LLAP_CTS:
typeName = "lapCTS";
break;
}
if (typeName)
atbridge_printf("LLAP[%d->%d] %s: %d bytes.\n", source, dest, typeName, size);
else
atbridge_printf("LLAP[%d->%d] %x: %d bytes.\n", source, dest, type, size);
/*for (size_t i = 0; i < size; i++)
atbridge_printf("%02x ", data[i]);
atbridge_printf("\n");*/
}
}
/** Reply to a control packet from the GS **/
static void llap_reply_control(at_node_t dest, at_node_t source, LLAP_TYPES type)
{
struct at_addr_t dest_addr = { 0, dest };
struct at_addr_t source_addr = { 0, source };
// Insert control packets at the head of the queue contrary to normal FIFO queue operation
// to ensure that control frames arrive in the intended order.
insert(&llap_port.out, dest_addr, source_addr, type, 0, 0);
}
/** Accept a data packet from the GS. **/
static void llap_handle_data(size_t size, byte data[])
{
at_node_t dest = data[0];
at_node_t source = data[1];
LLAP_TYPES type = (LLAP_TYPES)(data[2]);
const size_t data_size = size - 3;
byte* data_copy = (byte*)malloc(data_size);
memcpy(data_copy, data + 3, data_size);
struct at_addr_t dest_addr = { 0, dest };
struct at_addr_t source_addr = { 0, source };
enqueue(&llap_port.in, dest_addr, source_addr, type, data_size, data_copy);
}
/** Accept a control packet from the GS. **/
static void llap_handle_control(size_t size, byte data[])
{
at_node_t dest = data[0];
at_node_t source = data[1];
LLAP_TYPES type = (LLAP_TYPES)(data[2]);
struct at_addr_t addr = { atbridge_get_net(), dest };
switch (type)
{
case LLAP_ENQ:
// Require the GS to take a valid "client" address not known to be in use.
if (dest > 127 || dest == 0 || atbridge_address_used(&addr))
llap_reply_control(source, dest, LLAP_ACK);
break;
case LLAP_ACK:
break;
case LLAP_RTS:
if (dest != at_broadcast_node)
// The GS is trying to make a directed transmission. Provide the required RTS/CTS handshake.
// Note that broadcast packets do not require a CTS.
llap_reply_control(source, dest, LLAP_CTS);
break;
case LLAP_CTS:
// The GS sent a CTS. If the bridge has pending data, prepare to deliver the packet.
dialog_state = DIALOG_GOT_CTS;
break;
default:
break;
}
}
/** Occassionally, we receive an invalid packet from the GS. I'm unsure if this is due to a bug in GS/OS
or, more likely, a bug in the SCC emulation. Regardless, when such a thing does occur, discard the
current, corrupted dialog. Link errors are routine in real LocalTalk networks, and LocalTalk will recover.
**/
static void llap_reset_dialog()
{
dialog_state = DIALOG_READY;
last_frame_dcycs = 0;
// Discard packets until the queue is either empty or the next dialog starts (and dialogs begin with an RTS).
while (true)
{
struct packet_t* packet = queue_peek(&llap_port.out);
if (packet && (packet->type != LLAP_RTS))
{
packet = dequeue(&llap_port.out);
if (packet->data)
free(packet->data);
free(packet);
}
else
break;
}
}
/** Transfer (send) one LLAP packet from the GS. **/
void llap_enqueue_in(double dcycs, size_t size, byte data[])
{
atbridge_printf("<%0.0f> TX: ", dcycs);
llap_dump_packet(size, data);
if (size < LLAP_PACKET_MIN)
atbridge_printf("ATBridge: Dropping LLAP short packet.\n");
else if (size > LLAP_PACKET_MAX)
atbridge_printf("ATBridge: Dropping LLAP long packet.\n");
else
{
last_frame_dcycs = dcycs;
LLAP_TYPES type = (LLAP_TYPES)(data[2]);
switch (type)
{
case LLAP_DDP_SHORT:
case LLAP_DDP_LONG:
llap_handle_data(size, data);
break;
case LLAP_ENQ:
case LLAP_ACK:
case LLAP_RTS:
case LLAP_CTS:
llap_handle_control(size, data);
break;
default:
// Intentionally check for valid types and ingore packets with invalid types.
// Sometimes, the bridge gets invalid packets from the GS, which tends to break the bridge.
atbridge_printf("ATBridge: Dropping LLAP packet with invalid type.\n");
llap_reset_dialog();
}
}
}
/** Transfer (receive) one LLAP packet to the GS. **/
void llap_dequeue_out(double dcycs, size_t* size, byte* data[])
{
*size = 0;
// The LocalTalk protocol requires a minimum 400us gap between dialogs (called the IDG).
// If necessary, wait for the IDG.
if (dialog_state == DIALOG_WAIT_IDG)
{
if ((dcycs - dialog_end_dcycs) >= LLAP_IDG)
// The IDG is done.
dialog_state = DIALOG_READY;
else
// Continue waiting for the IDG.
return;
}
// The LocalTalk protocols requires a maximum 200us gap between frames within a dialog (called the IFG).
// If we exceed the IFG, the bridge must be stuck in an incomplete or corrupt dialog. In this case,
// discard the current dialog and try again.
if ((dialog_state != DIALOG_READY) && (last_frame_dcycs != 0) && ((dcycs - last_frame_dcycs) >= (GAP_TOLERANCE*LLAP_IFG)))
{
llap_reset_dialog();
atbridge_printf("ATBridge: Dialog reset due to IFG violation.\n");
}
struct packet_t* packet = queue_peek(&llap_port.out);
if ((dialog_state == DIALOG_READY) && (packet) && !(packet->type & 0x80) && (last_frame_dcycs != 0) && ((dcycs - last_frame_dcycs) >= (GAP_TOLERANCE*LLAP_IDG)))
{
llap_reset_dialog();
packet = queue_peek(&llap_port.out);
atbridge_printf("ATBridge: Dialog reset due to IDG violation.\n");
}
if (packet &&
((packet->type & 0x80) || /* Pass along control frames without waiting for a CTS. */
(!(packet->type & 0x80) && (packet->dest.node == at_broadcast_node) && (dialog_state == DIALOG_READY)) || /* Pass along broadcast frames, which don't wait for CTS frames. */
(!(packet->type & 0x80) && (packet->dest.node != at_broadcast_node) && (dialog_state == DIALOG_GOT_CTS)))) /* Pass along directed frames only after receiving a CTS handshake. */
{
dequeue(&llap_port.out);
// Prepend the LLAP header.
*size = packet->size + 3 + 2;
*data = (byte*)malloc(*size);
(*data)[0] = packet->dest.node;
(*data)[1] = packet->source.node;
(*data)[2] = packet->type;
// Insert the data into the new LLAP packet.
if (*size)
memcpy((*data) + 3, packet->data, packet->size);
// Fake a frame check sequence (FCS). Since our SCC emulation doesn't actually
// check the FCS, the value of the FCS doesn't matter.
(*data)[packet->size + 3 + 0] = 0xff;
(*data)[packet->size + 3 + 1] = 0xff;
atbridge_printf("<%0.0f> RX: ", dcycs);
llap_dump_packet(*size, *data);
if (packet->type & 0x80)
dialog_state = DIALOG_READY;
else
{
// This was the last packet in the dialog.
dialog_state = DIALOG_WAIT_IDG;
dialog_end_dcycs = dcycs;
}
last_frame_dcycs = dcycs;
free(packet->data);
free(packet);
}
}