cmsis_dap_tcp.c

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// SPDX-License-Identifier: GPL-2.0-or-later
 
/***************************************************************************
 *   Provides CMSIS-DAP protocol over a TCP/IP socket.                     *
 *   UART and SWO are currently unsupported.                               *
 *                                                                         *
 *   Copyright (C) 2025 by Brian Kuschak <bkuschak@gmail.com>              *
 *                                                                         *
 *   Adapted from cmsis_dap_usb_hid.c. Copyright (C) 2013-2018 by:         *
 *     Mickaël Thomas <mickael9@gmail.com>                                 *
 *     Maksym Hilliaka <oter@frozen-team.com>                              *
 *     Phillip Pearson <pp@myelin.co.nz>                                   *
 *     Paul Fertser <fercerpav@gmail.com>                                  *
 *     mike brown <mike@theshedworks.org.uk>                               *
 *     Spencer Oliver <spen@spen-soft.co.uk>                               *
 *                                                                         *
 ***************************************************************************/
 
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
 
#ifdef HAVE_NETDB_H
#include <netdb.h>
#endif
#ifdef HAVE_NETINET_TCP_H
#include <netinet/tcp.h>
#endif
#include <stdbool.h>
#include <string.h>
#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#include <sys/types.h>
 
#include "helper/command.h"
#include "helper/log.h"
#include "helper/replacements.h"
#include "helper/system.h"
#include "cmsis_dap.h"
 
#define STRINGIFY(x) #x
 
// If the protocol changes in the future, the SIGNATURE should also be changed.
#define DAP_PKT_HDR_SIGNATURE   0x00504144  // "DAP"
#define DAP_PKT_TYPE_REQUEST    0x01
#define DAP_PKT_TYPE_RESPONSE   0x02
 
#define CMSIS_DAP_TCP_PORT      4441        // Default. Can be overridden.
#define CMSIS_DAP_PACKET_SIZE   1024        // Max payload size not including
                                            // header.
 
/* When flushing after an error, the CMSIS-DAP driver assumes the pipeline is
 * empty if it doesn't get a response after a short 10 msec timeout. While this
 * works for USB, it may not work for TCP/IP due to higher network latency. TCP
 * response packets may take longer to arrive. We set a lower bound on timeout
 * for blocking reads, to give enough time for packets to arrive.
 *
 * The user may override this default value by setting the parameter
 * 'cmsis-dap tcp min_timeout'
 */
#define DEFAULT_MIN_TIMEOUT_MS  150
 
/* CMSIS-DAP requests are variable length. With CMSIS-DAP over USB, the
 * transfer sizes are preserved by the USB stack. However, TCP/IP is stream
 * oriented so we perform our own packetization to preserve the boundaries
 * between each request. This short header is prepended to each CMSIS-DAP
 * request and response before being sent over the socket. Little endian format
 * is used for multibyte values.
 */
struct __attribute__((packed)) cmsis_dap_tcp_packet_hdr {
    uint32_t signature;     // "DAP"
    uint16_t length;        // Not including header length.
    uint8_t packet_type;
    uint8_t reserved;       // Reserved for future use.
};
 
/* Defines for struct cmsis_dap_tcp_packet_hdr requested by reviewer. */
#define HEADER_SIGNATURE_OFFSET     0
#define HEADER_LENGTH_OFFSET        sizeof(uint32_t)
#define HEADER_PACKET_TYPE_OFFSET   (sizeof(uint32_t) + sizeof(uint16_t))
#define HEADER_RESERVED_OFFSET      (sizeof(uint32_t) + sizeof(uint16_t) + \
                                     sizeof(uint8_t))
#define HEADER_SIZE                 (sizeof(uint32_t) + sizeof(uint16_t) + \
                                     2 * sizeof(uint8_t))
 
struct cmsis_dap_backend_data {
    int sockfd;
};
 
static char *cmsis_dap_tcp_host;
static char cmsis_dap_tcp_port_default[] = STRINGIFY(CMSIS_DAP_TCP_PORT);
static char *cmsis_dap_tcp_port = cmsis_dap_tcp_port_default;
static int cmsis_dap_tcp_min_timeout_ms = DEFAULT_MIN_TIMEOUT_MS;
 
static void cmsis_dap_tcp_close(struct cmsis_dap *dap);
static int cmsis_dap_tcp_alloc(struct cmsis_dap *dap, unsigned int pkt_sz);
static void cmsis_dap_tcp_free(struct cmsis_dap *dap);
 
static int cmsis_dap_tcp_open(struct cmsis_dap *dap,
        uint16_t vids[] __attribute__((unused)),
        uint16_t pids[] __attribute__((unused)),
        const char *serial __attribute__((unused)))
{
    // Skip the open if the user has not provided a hostname.
    if (!cmsis_dap_tcp_host) {
        LOG_DEBUG("No TCP hostname, skipping open.");
        return ERROR_FAIL;
    }
 
    // Ignore vids, pids, serial. We use host and port subcommands instead.
 
    dap->bdata = malloc(sizeof(struct cmsis_dap_backend_data));
    if (!dap->bdata) {
        LOG_ERROR("CMSIS-DAP: unable to allocate memory");
        return ERROR_FAIL;
    }
 
    struct addrinfo hints = {
        .ai_family = AF_UNSPEC,
        .ai_socktype = SOCK_STREAM
    };
    struct addrinfo *result, *rp;
    int fd = 0;
 
    LOG_INFO("CMSIS-DAP: Connecting to %s:%s using TCP backend",
            cmsis_dap_tcp_host ? cmsis_dap_tcp_host : "localhost",
            cmsis_dap_tcp_port);
 
    /* Some of the following code was taken from remote_bitbang.c */
    /* Obtain address(es) matching host/port */
    int s = getaddrinfo(cmsis_dap_tcp_host, cmsis_dap_tcp_port, &hints,
            &result);
    if (s != 0) {
        LOG_ERROR("CMSIS-DAP: getaddrinfo: %s\n", gai_strerror(s));
        free(dap->bdata);
        return ERROR_FAIL;
    }
 
    /* getaddrinfo() returns a list of address structures.
     Try each address until we successfully connect(2).
     If socket(2) (or connect(2)) fails, we (close the socket
     and) try the next address. */
 
    for (rp = result; rp ; rp = rp->ai_next) {
        fd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
        if (fd == -1)
            continue;
 
        if (connect(fd, rp->ai_addr, rp->ai_addrlen) != -1) {
            LOG_DEBUG("Connected.");
            break; /* Success */
        }
 
        close(fd);
    }
 
    freeaddrinfo(result);
 
    if (!rp) { /* No address succeeded */
        LOG_ERROR("CMSIS-DAP: unable to connect to device %s:%s",
            cmsis_dap_tcp_host ? cmsis_dap_tcp_host : "localhost",
            cmsis_dap_tcp_port);
        log_socket_error("Failed to connect");
        free(dap->bdata);
        dap->bdata = NULL;
        return ERROR_FAIL;
    }
 
    /* Set NODELAY to minimize latency. */
    int one = 1;
    /* On Windows optval has to be a const char *. */
    setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, (const char *)&one, sizeof(one));
 
    dap->bdata->sockfd = fd;
 
    int retval = cmsis_dap_tcp_alloc(dap, CMSIS_DAP_PACKET_SIZE);
    if (retval != ERROR_OK) {
        cmsis_dap_tcp_close(dap);
        return retval;
    }
    return ERROR_OK;
}
 
static void cmsis_dap_tcp_close(struct cmsis_dap *dap)
{
    if (close_socket(dap->bdata->sockfd) != 0)
        log_socket_error("close_socket");
 
    if (dap->bdata)
        free(dap->bdata);
    dap->bdata = NULL;
    cmsis_dap_tcp_free(dap);
}
 
static inline int readall_socket(int handle, void *buffer, unsigned int count)
{
    // Return after all count bytes available, or timeout, or error.
    return recv(handle, buffer, count, MSG_WAITALL);
}
 
static inline int peekall_socket(int handle, void *buffer, unsigned int count)
{
    /* Data remains unread on the socket until recv() is called later without
     * the MSG_PEEK flag. Return after all count bytes available, or timeout,
     * or error.
     */
    return recv(handle, buffer, count, MSG_PEEK | MSG_WAITALL);
}
 
static int cmsis_dap_tcp_read(struct cmsis_dap *dap, int transfer_timeout_ms,
                              enum cmsis_dap_blocking blocking)
{
    int wait_ms = (blocking == CMSIS_DAP_NON_BLOCKING) ? 0 :
        transfer_timeout_ms;
    if (wait_ms) {
        LOG_DEBUG_IO("CMSIS-DAP: using tcp timeout %d msec", wait_ms);
 
        // Don't use very short timeouts with TCP/IP as it may not be as fast
        // to respond as USB. User configurable minimum value.
        if (wait_ms < cmsis_dap_tcp_min_timeout_ms) {
            wait_ms = cmsis_dap_tcp_min_timeout_ms;
            LOG_DEBUG_IO("CMSIS-DAP: extending timeout to %d msec", wait_ms);
        }
    }
    socket_recv_timeout(dap->bdata->sockfd, wait_ms);
 
    if (blocking == CMSIS_DAP_NON_BLOCKING)
        socket_nonblock(dap->bdata->sockfd);
    else
        socket_block(dap->bdata->sockfd);
 
    // Peek at the header first to find the length.
    int retval = peekall_socket(dap->bdata->sockfd, dap->packet_buffer,
            HEADER_SIZE);
    LOG_DEBUG_IO("Reading header returned %d", retval);
    if (retval == 0) {
        LOG_DEBUG_IO("CMSIS-DAP: tcp timeout reached 1");
        return ERROR_TIMEOUT_REACHED;
    } else if (retval == -1) {
        if (errno == EAGAIN || errno == EWOULDBLOCK) {
            if (blocking == CMSIS_DAP_NON_BLOCKING)
                return ERROR_TIMEOUT_REACHED;
 
            LOG_DEBUG_IO("CMSIS-DAP: tcp timeout reached 2. timeout = %d msec",
                    wait_ms);
            return ERROR_TIMEOUT_REACHED;
        }
 
        LOG_ERROR("CMSIS-DAP: error reading header");
        log_socket_error("peek_socket");
        return ERROR_FAIL;
    } else if (retval != HEADER_SIZE) {
        LOG_ERROR("CMSIS-DAP: short header read");
        log_socket_error("peek_socket header short read");
        return ERROR_FAIL;
    }
 
    struct cmsis_dap_tcp_packet_hdr header;
    header.signature = le_to_h_u32(dap->packet_buffer +
            HEADER_SIGNATURE_OFFSET);
    header.length = le_to_h_u16(dap->packet_buffer + HEADER_LENGTH_OFFSET);
    header.packet_type = dap->packet_buffer[HEADER_PACKET_TYPE_OFFSET];
    header.reserved = dap->packet_buffer[HEADER_RESERVED_OFFSET];
 
    if (header.signature != DAP_PKT_HDR_SIGNATURE) {
        LOG_ERROR("CMSIS-DAP: Unrecognized packet signature 0x%08x",
                header.signature);
        return ERROR_FAIL;
    } else if (header.packet_type != DAP_PKT_TYPE_RESPONSE) {
        LOG_ERROR("CMSIS-DAP: Unrecognized packet type 0x%02x",
                header.packet_type);
        return ERROR_FAIL;
    } else if (header.length + HEADER_SIZE > dap->packet_buffer_size) {
        LOG_ERROR("CMSIS-DAP: Packet length %d too large to fit.",
                header.length);
        return ERROR_FAIL;
    }
 
    // Read the complete packet.
    int read_len = HEADER_SIZE + header.length;
    LOG_DEBUG_IO("Reading %d bytes (%d payload)...", read_len, header.length);
    retval = readall_socket(dap->bdata->sockfd, dap->packet_buffer, read_len);
 
    if (retval == 0) {
        LOG_DEBUG_IO("CMSIS-DAP: tcp timeout reached 3");
        return ERROR_TIMEOUT_REACHED;
    } else if (retval == -1) {
        LOG_ERROR("CMSIS-DAP: error reading data");
        log_socket_error("read_socket");
        return ERROR_FAIL;
    } else if (retval != read_len) {
        LOG_ERROR("CMSIS-DAP: short read. retval = %d. read_len = %d. "
                "blocking = %s. wait_ms = %d", retval, read_len,
                (blocking == CMSIS_DAP_NON_BLOCKING) ? "yes" : "no", wait_ms);
        log_socket_error("read_socket short read");
        return ERROR_FAIL;
    }
    return retval;
}
 
static int cmsis_dap_tcp_write(struct cmsis_dap *dap, int txlen,
        int timeout_ms __attribute__((unused)))
{
    const unsigned int len = txlen + HEADER_SIZE;
    if (len > dap->packet_buffer_size) {
        LOG_ERROR("CMSIS-DAP: Packet length %d exceeds TCP buffer size!", len);
        return ERROR_FAIL;
    }
 
    /* Set the header values. */
    h_u32_to_le(dap->packet_buffer + HEADER_SIGNATURE_OFFSET,
            DAP_PKT_HDR_SIGNATURE);
    h_u16_to_le(dap->packet_buffer + HEADER_LENGTH_OFFSET, txlen);
    dap->packet_buffer[HEADER_PACKET_TYPE_OFFSET] = DAP_PKT_TYPE_REQUEST;
    dap->packet_buffer[HEADER_RESERVED_OFFSET] = 0;
 
    /* write data to device */
    LOG_DEBUG_IO("Writing %d bytes (%d payload)", len, txlen);
    int retval = write_socket(dap->bdata->sockfd, dap->packet_buffer, len);
    if (retval < 0) {
        log_socket_error("write_socket");
        return ERROR_FAIL;
    } else if (retval != (int)len) {
        LOG_ERROR("CMSIS-DAP: error writing data");
        log_socket_error("write_socket short write");
        return ERROR_FAIL;
    }
    return retval;
}
 
static int cmsis_dap_tcp_alloc(struct cmsis_dap *dap, unsigned int pkt_sz)
{
    // Reserve space for the packet header.
    unsigned int packet_buffer_size = pkt_sz + HEADER_SIZE;
    uint8_t *buf = malloc(packet_buffer_size);
    if (!buf) {
        LOG_ERROR("CMSIS-DAP: unable to allocate CMSIS-DAP packet buffer");
        return ERROR_FAIL;
    }
 
    dap->packet_buffer = buf;
    dap->packet_size = pkt_sz;
    dap->packet_usable_size = pkt_sz;
    dap->packet_buffer_size = packet_buffer_size;
 
    dap->command = dap->packet_buffer + HEADER_SIZE;
    dap->response = dap->packet_buffer + HEADER_SIZE;
    return ERROR_OK;
}
 
static void cmsis_dap_tcp_free(struct cmsis_dap *dap)
{
    free(dap->packet_buffer);
    dap->packet_buffer = NULL;
}
 
static void cmsis_dap_tcp_cancel_all(struct cmsis_dap *dap)
{
}
 
COMMAND_HANDLER(cmsis_dap_handle_tcp_port)
{
    if (CMD_ARGC != 1)
        return ERROR_COMMAND_SYNTAX_ERROR;
 
    if (cmsis_dap_tcp_port != cmsis_dap_tcp_port_default)
        free(cmsis_dap_tcp_port);
 
    cmsis_dap_tcp_port = strdup(CMD_ARGV[0]);
    if (!cmsis_dap_tcp_port) {
        LOG_ERROR("CMSIS-DAP: out of memory");
        return ERROR_FAIL;
    }
    return ERROR_OK;
}
 
COMMAND_HANDLER(cmsis_dap_handle_tcp_host)
{
    if (CMD_ARGC != 1)
        return ERROR_COMMAND_SYNTAX_ERROR;
 
    free(cmsis_dap_tcp_host);
    cmsis_dap_tcp_host = strdup(CMD_ARGV[0]);
    if (!cmsis_dap_tcp_host) {
        LOG_ERROR("CMSIS-DAP: out of memory");
        return ERROR_FAIL;
    }
    return ERROR_OK;
}
 
COMMAND_HANDLER(cmsis_dap_handle_tcp_min_timeout)
{
    if (CMD_ARGC != 1)
        return ERROR_COMMAND_SYNTAX_ERROR;
 
    COMMAND_PARSE_NUMBER(int, CMD_ARGV[0], cmsis_dap_tcp_min_timeout_ms);
    LOG_INFO("CMSIS-DAP: using minimum timeout of %d ms for TCP packets.",
            cmsis_dap_tcp_min_timeout_ms);
    return ERROR_OK;
}
 
const struct command_registration cmsis_dap_tcp_subcommand_handlers[] = {
    {
        .name = "host",
        .handler = &cmsis_dap_handle_tcp_host,
        .mode = COMMAND_CONFIG,
        .help = "set the host name to use (for TCP backend only)",
        .usage = "<host_name>",
    },
    {
        .name = "port",
        .handler = &cmsis_dap_handle_tcp_port,
        .mode = COMMAND_CONFIG,
        .help = "set the port number to use for DAP (for TCP backend only)",
        .usage = "<port_number>",
    },
    {
        .name = "min_timeout",
        .handler = &cmsis_dap_handle_tcp_min_timeout,
        .mode = COMMAND_CONFIG,
        .help = "set the minimum timeout in milliseconds to wait for response "
            "packets (for TCP backend only)",
        .usage = "<milliseconds>",
    },
    COMMAND_REGISTRATION_DONE
};
 
const struct cmsis_dap_backend cmsis_dap_tcp_backend = {
    .name = "tcp",
    .open = cmsis_dap_tcp_open,
    .close = cmsis_dap_tcp_close,
    .read = cmsis_dap_tcp_read,
    .write = cmsis_dap_tcp_write,
    .packet_buffer_alloc = cmsis_dap_tcp_alloc,
    .packet_buffer_free = cmsis_dap_tcp_free,
    .cancel_all = cmsis_dap_tcp_cancel_all,
};