cmsis_dap_usb_bulk.c

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// SPDX-License-Identifier: GPL-2.0-or-later
 
/***************************************************************************
 *   Copyright (C) 2018 by Mickaël Thomas                                  *
 *   mickael9@gmail.com                                                    *
 *                                                                         *
 *   Copyright (C) 2016 by Maksym Hilliaka                                 *
 *   oter@frozen-team.com                                                  *
 *                                                                         *
 *   Copyright (C) 2016 by Phillip Pearson                                 *
 *   pp@myelin.co.nz                                                       *
 *                                                                         *
 *   Copyright (C) 2014 by Paul Fertser                                    *
 *   fercerpav@gmail.com                                                   *
 *                                                                         *
 *   Copyright (C) 2013 by mike brown                                      *
 *   mike@theshedworks.org.uk                                              *
 *                                                                         *
 *   Copyright (C) 2013 by Spencer Oliver                                  *
 *   spen@spen-soft.co.uk                                                  *
 ***************************************************************************/
 
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
 
#include <helper/system.h>
#include <libusb.h>
#include <helper/log.h>
#include <helper/replacements.h>
#include <jtag/jtag.h>  /* ERROR_JTAG_DEVICE_ERROR only */
 
#include "cmsis_dap.h"
#include "libusb_helper.h"
 
enum {
    CMSIS_DAP_TRANSFER_PENDING = 0, /* must be 0, used in libusb_handle_events_completed */
    CMSIS_DAP_TRANSFER_IDLE,
    CMSIS_DAP_TRANSFER_COMPLETED
};
 
struct cmsis_dap_bulk_transfer {
    struct libusb_transfer *transfer;
    uint8_t *buffer;
    int status;     /* either CMSIS_DAP_TRANSFER_ enum or error code */
    int transferred;
};
 
struct cmsis_dap_backend_data {
    struct libusb_context *usb_ctx;
    struct libusb_device_handle *dev_handle;
    unsigned int ep_out;
    unsigned int ep_in;
    int interface;
 
    struct cmsis_dap_bulk_transfer command_transfers[MAX_PENDING_REQUESTS];
    struct cmsis_dap_bulk_transfer response_transfers[MAX_PENDING_REQUESTS];
};
 
static int cmsis_dap_usb_interface = -1;
 
static void cmsis_dap_usb_close(struct cmsis_dap *dap);
static int cmsis_dap_usb_alloc(struct cmsis_dap *dap, unsigned int pkt_sz);
static void cmsis_dap_usb_free(struct cmsis_dap *dap);
 
static int cmsis_dap_usb_open(struct cmsis_dap *dap, uint16_t vids[], uint16_t pids[], const char *serial)
{
    int err;
    struct libusb_context *ctx;
    struct libusb_device **device_list;
 
    err = libusb_init(&ctx);
    if (err) {
        LOG_ERROR("libusb initialization failed: %s", libusb_strerror(err));
        return ERROR_FAIL;
    }
 
    int num_devices = libusb_get_device_list(ctx, &device_list);
    if (num_devices < 0) {
        LOG_ERROR("could not enumerate USB devices: %s", libusb_strerror(num_devices));
        libusb_exit(ctx);
        return ERROR_FAIL;
    }
 
    for (int i = 0; i < num_devices; i++) {
        struct libusb_device *dev = device_list[i];
        struct libusb_device_descriptor dev_desc;
 
        err = libusb_get_device_descriptor(dev, &dev_desc);
        if (err) {
            LOG_ERROR("could not get device descriptor for device %d: %s", i, libusb_strerror(err));
            continue;
        }
 
        /* Match VID/PID */
 
        bool id_match = false;
        bool id_filter = vids[0] || pids[0];
        for (int id = 0; vids[id] || pids[id]; id++) {
            id_match = !vids[id] || dev_desc.idVendor == vids[id];
            id_match &= !pids[id] || dev_desc.idProduct == pids[id];
 
            if (id_match)
                break;
        }
 
        if (id_filter && !id_match)
            continue;
 
        /* Don't continue if we asked for a serial number and the device doesn't have one */
        if (dev_desc.iSerialNumber == 0 && serial && serial[0])
            continue;
 
        struct libusb_device_handle *dev_handle = NULL;
        err = libusb_open(dev, &dev_handle);
        if (err) {
            /* It's to be expected that most USB devices can't be opened
             * so only report an error if it was explicitly selected
             */
            if (id_filter) {
                LOG_ERROR("could not open device 0x%04x:0x%04x: %s",
                        dev_desc.idVendor, dev_desc.idProduct, libusb_strerror(err));
            } else {
                LOG_DEBUG("could not open device 0x%04x:0x%04x: %s",
                        dev_desc.idVendor, dev_desc.idProduct, libusb_strerror(err));
            }
            continue;
        }
 
        /* Match serial number */
 
        bool serial_match = false;
        char dev_serial[256] = {0};
        if (dev_desc.iSerialNumber > 0) {
            err = libusb_get_string_descriptor_ascii(
                    dev_handle, dev_desc.iSerialNumber,
                    (uint8_t *)dev_serial, sizeof(dev_serial));
 
            if (err < 0) {
                const char *msg = "could not read serial number for device 0x%04x:0x%04x: %s";
                if (serial)
                    LOG_WARNING(msg, dev_desc.idVendor, dev_desc.idProduct,
                                libusb_strerror(err));
                else
                    LOG_DEBUG(msg, dev_desc.idVendor, dev_desc.idProduct,
                                libusb_strerror(err));
            } else if (serial && strncmp(dev_serial, serial, sizeof(dev_serial)) == 0) {
                serial_match = true;
            }
        }
 
        if (serial && !serial_match) {
            libusb_close(dev_handle);
            continue;
        }
 
        /* Find the CMSIS-DAP string in product string */
 
        bool cmsis_dap_in_product_str = false;
        char product_string[256] = {0};
        if (dev_desc.iProduct > 0) {
            err = libusb_get_string_descriptor_ascii(
                    dev_handle, dev_desc.iProduct,
                    (uint8_t *)product_string, sizeof(product_string));
            if (err < 0) {
                LOG_WARNING("could not read product string for device 0x%04x:0x%04x: %s",
                        dev_desc.idVendor, dev_desc.idProduct, libusb_strerror(err));
            } else if (strstr(product_string, "CMSIS-DAP")) {
                LOG_DEBUG("found product string of 0x%04x:0x%04x '%s'",
                          dev_desc.idVendor, dev_desc.idProduct, product_string);
                cmsis_dap_in_product_str = true;
            }
        }
 
        bool device_identified_reliably = cmsis_dap_in_product_str
                                            || serial_match || id_match;
 
        /* Find the CMSIS-DAP interface */
 
        for (int config = 0; config < dev_desc.bNumConfigurations; config++) {
            struct libusb_config_descriptor *config_desc;
            err = libusb_get_config_descriptor(dev, config, &config_desc);
            if (err) {
                LOG_ERROR("could not get configuration descriptor %d for device 0x%04x:0x%04x: %s",
                        config, dev_desc.idVendor, dev_desc.idProduct, libusb_strerror(err));
                continue;
            }
 
            LOG_DEBUG("enumerating interfaces of 0x%04x:0x%04x",
                      dev_desc.idVendor, dev_desc.idProduct);
            int config_num = config_desc->bConfigurationValue;
            const struct libusb_interface_descriptor *intf_desc_candidate = NULL;
            const struct libusb_interface_descriptor *intf_desc_found = NULL;
 
            for (int interface = 0; interface < config_desc->bNumInterfaces; interface++) {
                const struct libusb_interface_descriptor *intf_desc = &config_desc->interface[interface].altsetting[0];
                int interface_num = intf_desc->bInterfaceNumber;
 
                /* Skip this interface if another one was requested explicitly */
                if (cmsis_dap_usb_interface != -1 && cmsis_dap_usb_interface != interface_num)
                    continue;
 
                /* CMSIS-DAP v2 spec says:
                 *
                 * CMSIS-DAP with default V2 configuration uses WinUSB and is therefore faster.
                 * Optionally support for streaming SWO trace is provided via an additional USB endpoint.
                 *
                 * The WinUSB configuration requires custom class support with the interface setting
                 *     Class Code: 0xFF (Vendor specific)
                 *     Subclass: 0x00
                 *     Protocol code: 0x00
                 *
                 * Depending on the configuration it uses the following USB endpoints which should be configured
                 * in the interface descriptor in this order:
                 *  - Endpoint 1: Bulk Out – used for commands received from host PC.
                 *  - Endpoint 2: Bulk In – used for responses send to host PC.
                 *  - Endpoint 3: Bulk In (optional) – used for streaming SWO trace (if enabled with SWO_STREAM).
                 */
 
                /* Search for "CMSIS-DAP" in the interface string */
                bool cmsis_dap_in_interface_str = false;
                if (intf_desc->iInterface != 0) {
 
                    char interface_str[256] = {0};
 
                    err = libusb_get_string_descriptor_ascii(
                            dev_handle, intf_desc->iInterface,
                            (uint8_t *)interface_str, sizeof(interface_str));
                    if (err < 0) {
                        LOG_DEBUG("could not read interface string %d for device 0x%04x:0x%04x: %s",
                                  intf_desc->iInterface,
                                  dev_desc.idVendor, dev_desc.idProduct,
                                  libusb_strerror(err));
                    } else if (strstr(interface_str, "CMSIS-DAP")) {
                        cmsis_dap_in_interface_str = true;
                        LOG_DEBUG("found interface %d string '%s'",
                                  interface_num, interface_str);
                    }
                }
 
                /* Bypass the following check if this interface was explicitly requested. */
                if (cmsis_dap_usb_interface == -1) {
                    if (!cmsis_dap_in_product_str && !cmsis_dap_in_interface_str)
                        continue;
                }
 
                /* check endpoints */
                if (intf_desc->bNumEndpoints < 2) {
                    LOG_DEBUG("skipping interface %d, has only %d endpoints",
                              interface_num, intf_desc->bNumEndpoints);
                    continue;
                }
 
                if ((intf_desc->endpoint[0].bmAttributes & 3) != LIBUSB_TRANSFER_TYPE_BULK ||
                        (intf_desc->endpoint[0].bEndpointAddress & 0x80) != LIBUSB_ENDPOINT_OUT) {
                    LOG_DEBUG("skipping interface %d, endpoint[0] is not bulk out",
                              interface_num);
                    continue;
                }
 
                if ((intf_desc->endpoint[1].bmAttributes & 3) != LIBUSB_TRANSFER_TYPE_BULK ||
                        (intf_desc->endpoint[1].bEndpointAddress & 0x80) != LIBUSB_ENDPOINT_IN) {
                    LOG_DEBUG("skipping interface %d, endpoint[1] is not bulk in",
                              interface_num);
                    continue;
                }
 
                /* We can rely on the interface is really CMSIS-DAP if
                 * - we've seen CMSIS-DAP in the interface string
                 * - config asked explicitly for an interface number
                 * - the device has only one interface
                 * The later two cases should be honored only if we know
                 * we are on the right device */
                bool intf_identified_reliably = cmsis_dap_in_interface_str
                            || (device_identified_reliably &&
                                    (cmsis_dap_usb_interface != -1
                                     || config_desc->bNumInterfaces == 1));
 
                if (intf_desc->bInterfaceClass != LIBUSB_CLASS_VENDOR_SPEC ||
                        intf_desc->bInterfaceSubClass != 0 || intf_desc->bInterfaceProtocol != 0) {
                    /* If the interface is reliably identified
                     * then we need not insist on setting USB class, subclass and protocol
                     * exactly as the specification requires.
                     * Just filter out the well known classes, mainly CDC and MSC.
                     * At least KitProg3 uses class 0 contrary to the specification */
                    if (intf_identified_reliably &&
                            (intf_desc->bInterfaceClass == 0 || intf_desc->bInterfaceClass > 0x12)) {
                        LOG_WARNING("Using CMSIS-DAPv2 interface %d with wrong class %" PRId8
                                  " subclass %" PRId8 " or protocol %" PRId8,
                                  interface_num,
                                  intf_desc->bInterfaceClass,
                                  intf_desc->bInterfaceSubClass,
                                  intf_desc->bInterfaceProtocol);
                    } else {
                        LOG_DEBUG("skipping interface %d, class %" PRId8
                                  " subclass %" PRId8 " protocol %" PRId8,
                                  interface_num,
                                  intf_desc->bInterfaceClass,
                                  intf_desc->bInterfaceSubClass,
                                  intf_desc->bInterfaceProtocol);
                        continue;
 
                    }
                }
 
                if (intf_identified_reliably) {
                    /* That's the one! */
                    intf_desc_found = intf_desc;
                    break;
                }
 
                if (!intf_desc_candidate && device_identified_reliably) {
                    /* This interface looks suitable for CMSIS-DAP. Store the pointer to it
                     * and keep searching for another one with CMSIS-DAP in interface string */
                    intf_desc_candidate = intf_desc;
                }
            }
 
            if (!intf_desc_found) {
                /* We were not able to identify reliably which interface is CMSIS-DAP.
                 * Let's use the first suitable if we found one */
                intf_desc_found = intf_desc_candidate;
            }
 
            if (!intf_desc_found) {
                libusb_free_config_descriptor(config_desc);
                continue;
            }
 
            /* We've chosen an interface, connect to it */
            int interface_num = intf_desc_found->bInterfaceNumber;
            int packet_size = intf_desc_found->endpoint[0].wMaxPacketSize;
            int ep_out = intf_desc_found->endpoint[0].bEndpointAddress;
            int ep_in = intf_desc_found->endpoint[1].bEndpointAddress;
 
            libusb_free_config_descriptor(config_desc);
            libusb_free_device_list(device_list, true);
 
            LOG_INFO("Using CMSIS-DAPv2 interface with VID:PID=0x%04x:0x%04x, serial=%s",
                    dev_desc.idVendor, dev_desc.idProduct, dev_serial);
 
            int current_config;
            err = libusb_get_configuration(dev_handle, &current_config);
            if (err) {
                LOG_ERROR("could not find current configuration: %s", libusb_strerror(err));
                libusb_close(dev_handle);
                libusb_exit(ctx);
                return ERROR_FAIL;
            }
 
            if (config_num != current_config) {
                err = libusb_set_configuration(dev_handle, config_num);
                if (err) {
                    LOG_ERROR("could not set configuration: %s", libusb_strerror(err));
                    libusb_close(dev_handle);
                    libusb_exit(ctx);
                    return ERROR_FAIL;
                }
            }
 
            err = libusb_claim_interface(dev_handle, interface_num);
            if (err)
                LOG_WARNING("could not claim interface: %s", libusb_strerror(err));
 
            dap->bdata = calloc(1, sizeof(struct cmsis_dap_backend_data));
            if (!dap->bdata) {
                LOG_ERROR("unable to allocate memory");
                libusb_release_interface(dev_handle, interface_num);
                libusb_close(dev_handle);
                libusb_exit(ctx);
                return ERROR_FAIL;
            }
 
            dap->bdata->usb_ctx = ctx;
            dap->bdata->dev_handle = dev_handle;
            dap->bdata->ep_out = ep_out;
            dap->bdata->ep_in = ep_in;
            dap->bdata->interface = interface_num;
 
            for (unsigned int idx = 0; idx < MAX_PENDING_REQUESTS; idx++) {
                dap->bdata->command_transfers[idx].status = CMSIS_DAP_TRANSFER_IDLE;
                dap->bdata->command_transfers[idx].transfer = libusb_alloc_transfer(0);
                if (!dap->bdata->command_transfers[idx].transfer) {
                    LOG_ERROR("unable to allocate USB transfer");
                    cmsis_dap_usb_close(dap);
                    return ERROR_FAIL;
                }
 
                dap->bdata->response_transfers[idx].status = CMSIS_DAP_TRANSFER_IDLE;
                dap->bdata->response_transfers[idx].transfer = libusb_alloc_transfer(0);
                if (!dap->bdata->response_transfers[idx].transfer) {
                    LOG_ERROR("unable to allocate USB transfer");
                    cmsis_dap_usb_close(dap);
                    return ERROR_FAIL;
                }
            }
 
            err = cmsis_dap_usb_alloc(dap, packet_size);
            if (err != ERROR_OK)
                cmsis_dap_usb_close(dap);
 
            return err;
        }
 
        libusb_close(dev_handle);
    }
 
    libusb_free_device_list(device_list, true);
 
    libusb_exit(ctx);
    return ERROR_FAIL;
}
 
static void cmsis_dap_usb_close(struct cmsis_dap *dap)
{
    for (unsigned int i = 0; i < MAX_PENDING_REQUESTS; i++) {
        if (dap->bdata->command_transfers[i].status == CMSIS_DAP_TRANSFER_PENDING) {
            LOG_DEBUG("busy command USB transfer at %u", dap->pending_fifo_put_idx);
            struct timeval tv = {
                .tv_sec = 1,
                .tv_usec = 1000
            };
            /* Complete pending commands */
            int res = libusb_handle_events_timeout_completed(dap->bdata->usb_ctx, &tv, NULL);
            if (res == 0)
                libusb_free_transfer(dap->bdata->command_transfers[i].transfer);
        } else {
            libusb_free_transfer(dap->bdata->command_transfers[i].transfer);
        }
        libusb_free_transfer(dap->bdata->response_transfers[i].transfer);
    }
    cmsis_dap_usb_free(dap);
    libusb_release_interface(dap->bdata->dev_handle, dap->bdata->interface);
    libusb_close(dap->bdata->dev_handle);
    libusb_exit(dap->bdata->usb_ctx);
    free(dap->bdata);
    dap->bdata = NULL;
}
 
static void LIBUSB_CALL cmsis_dap_usb_callback(struct libusb_transfer *transfer)
{
    struct cmsis_dap_bulk_transfer *tr;
 
    tr = (struct cmsis_dap_bulk_transfer *)transfer->user_data;
    if (transfer->status == LIBUSB_TRANSFER_COMPLETED) {
        tr->status = CMSIS_DAP_TRANSFER_COMPLETED;
        tr->transferred = transfer->actual_length;
    } else if (transfer->status == LIBUSB_TRANSFER_TIMED_OUT) {
        tr->status = ERROR_TIMEOUT_REACHED;
    } else {
        tr->status = ERROR_JTAG_DEVICE_ERROR;
    }
}
 
static int cmsis_dap_usb_read(struct cmsis_dap *dap, int transfer_timeout_ms,
                              enum cmsis_dap_blocking blocking)
{
    int transferred = 0;
    int err;
    struct cmsis_dap_bulk_transfer *tr;
    tr = &dap->bdata->response_transfers[dap->pending_fifo_get_idx];
 
    if (tr->status == CMSIS_DAP_TRANSFER_IDLE) {
        libusb_fill_bulk_transfer(tr->transfer,
                                  dap->bdata->dev_handle, dap->bdata->ep_in,
                                  tr->buffer, dap->packet_size,
                                  &cmsis_dap_usb_callback, tr,
                                  transfer_timeout_ms);
        LOG_DEBUG_IO("submit read @ %u", dap->pending_fifo_get_idx);
        tr->status = CMSIS_DAP_TRANSFER_PENDING;
        err = libusb_submit_transfer(tr->transfer);
        if (err) {
            tr->status = CMSIS_DAP_TRANSFER_IDLE;
            LOG_ERROR("error submitting USB read: %s", libusb_strerror(err));
            return ERROR_FAIL;
        }
    }
 
    struct timeval tv;
    if (blocking == CMSIS_DAP_NON_BLOCKING) {
        tv.tv_sec = 0;
        tv.tv_usec = 0;
    } else {
        tv.tv_sec = transfer_timeout_ms / 1000;
        tv.tv_usec = transfer_timeout_ms % 1000 * 1000;
    }
 
    while (tr->status == CMSIS_DAP_TRANSFER_PENDING) {
        err = libusb_handle_events_timeout_completed(dap->bdata->usb_ctx, &tv,
                                                 &tr->status);
        if (err) {
            LOG_ERROR("error handling USB events: %s", libusb_strerror(err));
            return ERROR_FAIL;
        }
        if (tv.tv_sec == 0 && tv.tv_usec == 0)
            break;
    }
 
    if (tr->status < 0 || tr->status == CMSIS_DAP_TRANSFER_COMPLETED) {
        /* Check related command request for an error */
        struct cmsis_dap_bulk_transfer *tr_cmd;
        tr_cmd = &dap->bdata->command_transfers[dap->pending_fifo_get_idx];
        if (tr_cmd->status < 0) {
            err = tr_cmd->status;
            tr_cmd->status = CMSIS_DAP_TRANSFER_IDLE;
            if (err != ERROR_TIMEOUT_REACHED)
                LOG_ERROR("error writing USB data");
            else
                LOG_DEBUG("command write USB timeout @ %u", dap->pending_fifo_get_idx);
 
            return err;
        }
        if (tr_cmd->status == CMSIS_DAP_TRANSFER_COMPLETED)
            tr_cmd->status = CMSIS_DAP_TRANSFER_IDLE;
    }
 
    if (tr->status < 0) {
        err = tr->status;
        tr->status = CMSIS_DAP_TRANSFER_IDLE;
        if (err != ERROR_TIMEOUT_REACHED)
            LOG_ERROR("error reading USB data");
        else
            LOG_DEBUG("USB timeout @ %u", dap->pending_fifo_get_idx);
 
        return err;
    }
 
    if (tr->status == CMSIS_DAP_TRANSFER_COMPLETED) {
        transferred = tr->transferred;
        LOG_DEBUG_IO("completed read @ %u, transferred %i",
                     dap->pending_fifo_get_idx, transferred);
        memcpy(dap->packet_buffer, tr->buffer, transferred);
        memset(&dap->packet_buffer[transferred], 0, dap->packet_buffer_size - transferred);
        tr->status = CMSIS_DAP_TRANSFER_IDLE;
    }
 
    return transferred;
}
 
static int cmsis_dap_usb_write(struct cmsis_dap *dap, int txlen, int timeout_ms)
{
    int err;
    struct cmsis_dap_bulk_transfer *tr;
    tr = &dap->bdata->command_transfers[dap->pending_fifo_put_idx];
 
    if (tr->status == CMSIS_DAP_TRANSFER_PENDING) {
        LOG_DEBUG_IO("busy command USB transfer at %u", dap->pending_fifo_put_idx);
        struct timeval tv = {
            .tv_sec = timeout_ms / 1000,
            .tv_usec = timeout_ms % 1000 * 1000
        };
        libusb_handle_events_timeout_completed(dap->bdata->usb_ctx, &tv, &tr->status);
    }
    if (tr->status < 0) {
        if (tr->status != ERROR_TIMEOUT_REACHED)
            LOG_ERROR("error writing USB data, late detect");
        else
            LOG_DEBUG("USB write timeout @ %u, late detect", dap->pending_fifo_get_idx);
        tr->status = CMSIS_DAP_TRANSFER_IDLE;
    }
    if (tr->status == CMSIS_DAP_TRANSFER_COMPLETED) {
        LOG_DEBUG_IO("USB write: late transfer competed");
        tr->status = CMSIS_DAP_TRANSFER_IDLE;
    }
    if (tr->status != CMSIS_DAP_TRANSFER_IDLE) {
        libusb_cancel_transfer(tr->transfer);
        /* TODO: switch to less verbose errors and wait for USB working again */
        return ERROR_JTAG_DEVICE_ERROR;
    }
 
    memcpy(tr->buffer, dap->packet_buffer, txlen);
 
    libusb_fill_bulk_transfer(tr->transfer,
                              dap->bdata->dev_handle, dap->bdata->ep_out,
                              tr->buffer, txlen,
                              &cmsis_dap_usb_callback, tr,
                              timeout_ms);
 
    LOG_DEBUG_IO("submit write @ %u", dap->pending_fifo_put_idx);
    tr->status = CMSIS_DAP_TRANSFER_PENDING;
    err = libusb_submit_transfer(tr->transfer);
    if (err) {
        if (err == LIBUSB_ERROR_BUSY)
            libusb_cancel_transfer(tr->transfer);
        else
            tr->status = CMSIS_DAP_TRANSFER_IDLE;
 
        LOG_ERROR("error submitting USB write: %s", libusb_strerror(err));
        return ERROR_FAIL;
    }
 
    return ERROR_OK;
}
 
static int cmsis_dap_usb_alloc(struct cmsis_dap *dap, unsigned int pkt_sz)
{
    dap->packet_buffer = malloc(pkt_sz);
    if (!dap->packet_buffer) {
        LOG_ERROR("unable to allocate CMSIS-DAP packet buffer");
        return ERROR_FAIL;
    }
 
    dap->packet_size = pkt_sz;
    dap->packet_buffer_size = pkt_sz;
    /* Prevent sending zero size USB packets */
    dap->packet_usable_size = pkt_sz - 1;
 
    dap->command = dap->packet_buffer;
    dap->response = dap->packet_buffer;
 
    struct cmsis_dap_backend_data *bdata = dap->bdata;
    for (unsigned int i = 0; i < MAX_PENDING_REQUESTS; i++) {
        bdata->command_transfers[i].buffer =
            oocd_libusb_dev_mem_alloc(bdata->dev_handle, pkt_sz);
 
        bdata->response_transfers[i].buffer =
            oocd_libusb_dev_mem_alloc(bdata->dev_handle, pkt_sz);
 
        if (!bdata->command_transfers[i].buffer
            || !bdata->response_transfers[i].buffer) {
            LOG_ERROR("unable to allocate CMSIS-DAP pending packet buffer");
            return ERROR_FAIL;
        }
    }
    return ERROR_OK;
}
 
static void cmsis_dap_usb_free(struct cmsis_dap *dap)
{
    struct cmsis_dap_backend_data *bdata = dap->bdata;
 
    for (unsigned int i = 0; i < MAX_PENDING_REQUESTS; i++) {
        oocd_libusb_dev_mem_free(bdata->dev_handle,
            bdata->command_transfers[i].buffer, dap->packet_size);
        oocd_libusb_dev_mem_free(bdata->dev_handle,
            bdata->response_transfers[i].buffer, dap->packet_size);
        bdata->command_transfers[i].buffer = NULL;
        bdata->response_transfers[i].buffer = NULL;
    }
 
    free(dap->packet_buffer);
    dap->packet_buffer = NULL;
    dap->command = NULL;
    dap->response = NULL;
}
 
static void cmsis_dap_usb_cancel_all(struct cmsis_dap *dap)
{
    for (unsigned int i = 0; i < MAX_PENDING_REQUESTS; i++) {
        if (dap->bdata->command_transfers[i].status == CMSIS_DAP_TRANSFER_PENDING)
            libusb_cancel_transfer(dap->bdata->command_transfers[i].transfer);
        if (dap->bdata->response_transfers[i].status == CMSIS_DAP_TRANSFER_PENDING)
            libusb_cancel_transfer(dap->bdata->response_transfers[i].transfer);
 
        dap->bdata->command_transfers[i].status = CMSIS_DAP_TRANSFER_IDLE;
        dap->bdata->response_transfers[i].status = CMSIS_DAP_TRANSFER_IDLE;
    }
}
 
COMMAND_HANDLER(cmsis_dap_handle_usb_interface_command)
{
    if (CMD_ARGC == 1)
        COMMAND_PARSE_NUMBER(int, CMD_ARGV[0], cmsis_dap_usb_interface);
    else
        LOG_ERROR("expected exactly one argument to cmsis_dap_usb_interface <interface_number>");
 
    return ERROR_OK;
}
 
const struct command_registration cmsis_dap_usb_subcommand_handlers[] = {
    {
        .name = "interface",
        .handler = &cmsis_dap_handle_usb_interface_command,
        .mode = COMMAND_CONFIG,
        .help = "set the USB interface number to use (for USB bulk backend only)",
        .usage = "<interface_number>",
    },
    COMMAND_REGISTRATION_DONE
};
 
const struct cmsis_dap_backend cmsis_dap_usb_backend = {
    .name = "usb_bulk",
    .open = cmsis_dap_usb_open,
    .close = cmsis_dap_usb_close,
    .read = cmsis_dap_usb_read,
    .write = cmsis_dap_usb_write,
    .packet_buffer_alloc = cmsis_dap_usb_alloc,
    .packet_buffer_free = cmsis_dap_usb_free,
    .cancel_all = cmsis_dap_usb_cancel_all,
};