2 * This file is part of the libsigrok project.
4 * Copyright (C) 2014 Aurelien Jacobs <aurel@gnuage.org>
6 * This program is free software: you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation, either version 3 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <libsigrok/libsigrok.h>
24 #include "libsigrok-internal.h"
27 #define LOG_PREFIX "scpi_usbtmc"
29 #define MAX_TRANSFER_LENGTH 2048
30 #define TRANSFER_TIMEOUT 1000
32 struct scpi_usbtmc_libusb {
33 struct sr_context *ctx;
34 struct sr_usb_dev_inst *usb;
35 int detached_kernel_driver;
40 uint8_t usbtmc_int_cap;
41 uint8_t usbtmc_dev_cap;
42 uint8_t usb488_dev_cap;
44 uint8_t bulkin_attributes;
45 uint8_t buffer[MAX_TRANSFER_LENGTH];
47 int response_bytes_read;
51 /* Some USBTMC-specific enums, as defined in the USBTMC standard. */
52 #define SUBCLASS_USBTMC 0x03
53 #define USBTMC_USB488 0x01
56 /* USBTMC control requests */
57 INITIATE_ABORT_BULK_OUT = 1,
58 CHECK_ABORT_BULK_OUT_STATUS = 2,
59 INITIATE_ABORT_BULK_IN = 3,
60 CHECK_ABORT_BULK_IN_STATUS = 4,
62 CHECK_CLEAR_STATUS = 6,
66 /* USB488 control requests */
67 READ_STATUS_BYTE = 128,
73 /* USBTMC status codes */
74 #define USBTMC_STATUS_SUCCESS 0x01
76 /* USBTMC capabilities */
77 #define USBTMC_INT_CAP_LISTEN_ONLY 0x01
78 #define USBTMC_INT_CAP_TALK_ONLY 0x02
79 #define USBTMC_INT_CAP_INDICATOR 0x04
81 #define USBTMC_DEV_CAP_TERMCHAR 0x01
83 #define USB488_DEV_CAP_DT1 0x01
84 #define USB488_DEV_CAP_RL1 0x02
85 #define USB488_DEV_CAP_SR1 0x04
86 #define USB488_DEV_CAP_SCPI 0x08
88 /* Bulk messages constants */
89 #define USBTMC_BULK_HEADER_SIZE 12
91 /* Bulk MsgID values */
92 #define DEV_DEP_MSG_OUT 1
93 #define REQUEST_DEV_DEP_MSG_IN 2
94 #define DEV_DEP_MSG_IN 2
96 /* bmTransferAttributes */
98 #define TERM_CHAR_ENABLED 0x02
100 struct usbtmc_blacklist {
105 /* Devices that publish RL1 support, but don't support it. */
106 static struct usbtmc_blacklist blacklist_remote[] = {
107 { 0x1ab1, 0x0588 }, /* Rigol DS1000 series */
108 { 0x1ab1, 0x04b0 }, /* Rigol DS2000 series */
109 { 0x1ab1, 0x04b1 }, /* Rigol DS4000 series */
110 { 0x0957, 0x0588 }, /* Agilent DSO1000 series (rebadged Rigol DS1000) */
111 { 0x0b21, 0xffff }, /* All Yokogawa devices */
112 { 0xf4ec, 0xffff }, /* All Siglent SDS devices */
116 /* Devices that shall get reset during open(). */
117 static struct usbtmc_blacklist whitelist_usb_reset[] = {
118 { 0xf4ec, 0xffff }, /* All Siglent SDS devices */
122 static GSList *scpi_usbtmc_libusb_scan(struct drv_context *drvc)
124 struct libusb_device **devlist;
125 struct libusb_device_descriptor des;
126 struct libusb_config_descriptor *confdes;
127 const struct libusb_interface_descriptor *intfdes;
128 GSList *resources = NULL;
129 int confidx, intfidx, ret, i;
132 ret = libusb_get_device_list(drvc->sr_ctx->libusb_ctx, &devlist);
134 sr_err("Failed to get device list: %s.",
135 libusb_error_name(ret));
138 for (i = 0; devlist[i]; i++) {
139 libusb_get_device_descriptor(devlist[i], &des);
141 for (confidx = 0; confidx < des.bNumConfigurations; confidx++) {
142 if ((ret = libusb_get_config_descriptor(devlist[i], confidx, &confdes)) < 0) {
143 if (ret != LIBUSB_ERROR_NOT_FOUND)
144 sr_dbg("Failed to get configuration descriptor: %s, "
145 "ignoring device.", libusb_error_name(ret));
148 for (intfidx = 0; intfidx < confdes->bNumInterfaces; intfidx++) {
149 intfdes = confdes->interface[intfidx].altsetting;
150 if (intfdes->bInterfaceClass != LIBUSB_CLASS_APPLICATION ||
151 intfdes->bInterfaceSubClass != SUBCLASS_USBTMC ||
152 intfdes->bInterfaceProtocol != USBTMC_USB488)
154 sr_dbg("Found USBTMC device (VID:PID = %04x:%04x, "
155 "bus.address = %d.%d).", des.idVendor, des.idProduct,
156 libusb_get_bus_number(devlist[i]),
157 libusb_get_device_address(devlist[i]));
158 res = g_strdup_printf("usbtmc/%d.%d",
159 libusb_get_bus_number(devlist[i]),
160 libusb_get_device_address(devlist[i]));
161 resources = g_slist_append(resources, res);
163 libusb_free_config_descriptor(confdes);
166 libusb_free_device_list(devlist, 1);
168 /* No log message for #devices found (caller will log that). */
173 static int scpi_usbtmc_libusb_dev_inst_new(void *priv, struct drv_context *drvc,
174 const char *resource, char **params, const char *serialcomm)
176 struct scpi_usbtmc_libusb *uscpi = priv;
182 if (!params || !params[1]) {
183 sr_err("Invalid parameters.");
187 uscpi->ctx = drvc->sr_ctx;
188 devices = sr_usb_find(uscpi->ctx->libusb_ctx, params[1]);
189 if (g_slist_length(devices) != 1) {
190 sr_err("Failed to find USB device '%s'.", params[1]);
191 g_slist_free_full(devices, (GDestroyNotify)sr_usb_dev_inst_free);
194 uscpi->usb = devices->data;
195 g_slist_free(devices);
200 static int check_usbtmc_blacklist(struct usbtmc_blacklist *blacklist,
201 uint16_t vid, uint16_t pid)
205 for (i = 0; blacklist[i].vid; i++) {
206 if ((blacklist[i].vid == vid && blacklist[i].pid == 0xFFFF) ||
207 (blacklist[i].vid == vid && blacklist[i].pid == pid))
214 static int scpi_usbtmc_remote(struct scpi_usbtmc_libusb *uscpi)
216 struct sr_usb_dev_inst *usb = uscpi->usb;
217 struct libusb_device *dev;
218 struct libusb_device_descriptor des;
222 if (!(uscpi->usb488_dev_cap & USB488_DEV_CAP_RL1))
225 dev = libusb_get_device(usb->devhdl);
226 libusb_get_device_descriptor(dev, &des);
227 if (check_usbtmc_blacklist(blacklist_remote, des.idVendor, des.idProduct))
230 sr_dbg("Locking out local control.");
231 ret = libusb_control_transfer(usb->devhdl, LIBUSB_ENDPOINT_IN |
232 LIBUSB_REQUEST_TYPE_CLASS | LIBUSB_RECIPIENT_INTERFACE,
233 REN_CONTROL, 1, uscpi->interface, &status, 1, TRANSFER_TIMEOUT);
234 if (ret < 0 || status != USBTMC_STATUS_SUCCESS) {
236 sr_dbg("Failed to enter REN state: %s.", libusb_error_name(ret));
238 sr_dbg("Failed to enter REN state: USBTMC status %d.", status);
242 ret = libusb_control_transfer(usb->devhdl, LIBUSB_ENDPOINT_IN |
243 LIBUSB_REQUEST_TYPE_CLASS | LIBUSB_RECIPIENT_INTERFACE,
244 LOCAL_LOCKOUT, 0, uscpi->interface, &status, 1,
246 if (ret < 0 || status != USBTMC_STATUS_SUCCESS) {
248 sr_dbg("Failed to enter local lockout state: %s.",
249 libusb_error_name(ret));
251 sr_dbg("Failed to enter local lockout state: USBTMC "
252 "status %d.", status);
259 static void scpi_usbtmc_local(struct scpi_usbtmc_libusb *uscpi)
261 struct sr_usb_dev_inst *usb = uscpi->usb;
262 struct libusb_device *dev;
263 struct libusb_device_descriptor des;
267 if (!(uscpi->usb488_dev_cap & USB488_DEV_CAP_RL1))
270 dev = libusb_get_device(usb->devhdl);
271 libusb_get_device_descriptor(dev, &des);
272 if (check_usbtmc_blacklist(blacklist_remote, des.idVendor, des.idProduct))
275 sr_dbg("Returning local control.");
276 ret = libusb_control_transfer(usb->devhdl, LIBUSB_ENDPOINT_IN |
277 LIBUSB_REQUEST_TYPE_CLASS | LIBUSB_RECIPIENT_INTERFACE,
278 GO_TO_LOCAL, 0, uscpi->interface, &status, 1, TRANSFER_TIMEOUT);
279 if (ret < 0 || status != USBTMC_STATUS_SUCCESS) {
281 sr_dbg("Failed to clear local lockout state: %s.",
282 libusb_error_name(ret));
284 sr_dbg("Failed to clear local lockout state: USBTMC "
285 "status %d.", status);
291 static int scpi_usbtmc_libusb_open(struct sr_scpi_dev_inst *scpi)
293 struct scpi_usbtmc_libusb *uscpi = scpi->priv;
294 struct sr_usb_dev_inst *usb = uscpi->usb;
295 struct libusb_device *dev;
296 struct libusb_device_descriptor des;
297 struct libusb_config_descriptor *confdes;
298 const struct libusb_interface_descriptor *intfdes;
299 const struct libusb_endpoint_descriptor *ep;
300 int confidx, intfidx, epidx, config = 0, current_config;
301 uint8_t capabilities[24];
308 if (sr_usb_open(uscpi->ctx->libusb_ctx, usb) != SR_OK)
311 dev = libusb_get_device(usb->devhdl);
312 libusb_get_device_descriptor(dev, &des);
314 for (confidx = 0; confidx < des.bNumConfigurations; confidx++) {
315 if ((ret = libusb_get_config_descriptor(dev, confidx, &confdes)) < 0) {
316 if (ret != LIBUSB_ERROR_NOT_FOUND)
317 sr_dbg("Failed to get configuration descriptor: %s, "
318 "ignoring device.", libusb_error_name(ret));
321 for (intfidx = 0; intfidx < confdes->bNumInterfaces; intfidx++) {
322 intfdes = confdes->interface[intfidx].altsetting;
323 if (intfdes->bInterfaceClass != LIBUSB_CLASS_APPLICATION ||
324 intfdes->bInterfaceSubClass != SUBCLASS_USBTMC ||
325 intfdes->bInterfaceProtocol != USBTMC_USB488)
327 uscpi->interface = intfdes->bInterfaceNumber;
328 config = confdes->bConfigurationValue;
329 sr_dbg("Interface %d configuration %d.", uscpi->interface, config);
330 for (epidx = 0; epidx < intfdes->bNumEndpoints; epidx++) {
331 ep = &intfdes->endpoint[epidx];
332 if (ep->bmAttributes == LIBUSB_TRANSFER_TYPE_BULK &&
333 !(ep->bEndpointAddress & (LIBUSB_ENDPOINT_DIR_MASK))) {
334 uscpi->bulk_out_ep = ep->bEndpointAddress;
335 sr_dbg("Bulk OUT EP %d", uscpi->bulk_out_ep);
337 if (ep->bmAttributes == LIBUSB_TRANSFER_TYPE_BULK &&
338 ep->bEndpointAddress & (LIBUSB_ENDPOINT_DIR_MASK)) {
339 uscpi->bulk_in_ep = ep->bEndpointAddress;
340 sr_dbg("Bulk IN EP %d", uscpi->bulk_in_ep & 0x7f);
342 if (ep->bmAttributes == LIBUSB_TRANSFER_TYPE_INTERRUPT &&
343 ep->bEndpointAddress & (LIBUSB_ENDPOINT_DIR_MASK)) {
344 uscpi->interrupt_ep = ep->bEndpointAddress;
345 sr_dbg("Interrupt EP %d", uscpi->interrupt_ep & 0x7f);
350 libusb_free_config_descriptor(confdes);
356 sr_err("Failed to find USBTMC interface.");
360 if (libusb_kernel_driver_active(usb->devhdl, uscpi->interface) == 1) {
361 if ((ret = libusb_detach_kernel_driver(usb->devhdl,
362 uscpi->interface)) < 0) {
363 sr_err("Failed to detach kernel driver: %s.",
364 libusb_error_name(ret));
367 uscpi->detached_kernel_driver = 1;
370 if (libusb_get_configuration(usb->devhdl, ¤t_config) == 0
371 && current_config != config) {
372 if ((ret = libusb_set_configuration(usb->devhdl, config)) < 0) {
373 sr_err("Failed to set configuration: %s.",
374 libusb_error_name(ret));
379 if ((ret = libusb_claim_interface(usb->devhdl, uscpi->interface)) < 0) {
380 sr_err("Failed to claim interface: %s.",
381 libusb_error_name(ret));
385 /* Optionally reset the USB device. */
386 do_reset = check_usbtmc_blacklist(whitelist_usb_reset,
387 des.idVendor, des.idProduct);
389 libusb_reset_device(usb->devhdl);
391 /* Get capabilities. */
392 ret = libusb_control_transfer(usb->devhdl, LIBUSB_ENDPOINT_IN |
393 LIBUSB_REQUEST_TYPE_CLASS | LIBUSB_RECIPIENT_INTERFACE,
394 GET_CAPABILITIES, 0, uscpi->interface, capabilities,
395 sizeof(capabilities), TRANSFER_TIMEOUT);
396 if (ret == sizeof(capabilities)) {
397 uscpi->usbtmc_int_cap = capabilities[ 4];
398 uscpi->usbtmc_dev_cap = capabilities[ 5];
399 uscpi->usb488_dev_cap = capabilities[15];
401 sr_dbg("Device capabilities: %s%s%s%s%s, %s, %s",
402 uscpi->usb488_dev_cap & USB488_DEV_CAP_SCPI ? "SCPI, " : "",
403 uscpi->usbtmc_dev_cap & USBTMC_DEV_CAP_TERMCHAR ? "TermChar, ": "",
404 uscpi->usbtmc_int_cap & USBTMC_INT_CAP_LISTEN_ONLY ? "L3, " :
405 uscpi->usbtmc_int_cap & USBTMC_INT_CAP_TALK_ONLY ? "" : "L4, ",
406 uscpi->usbtmc_int_cap & USBTMC_INT_CAP_TALK_ONLY ? "T5, " :
407 uscpi->usbtmc_int_cap & USBTMC_INT_CAP_LISTEN_ONLY ? "" : "T6, ",
408 uscpi->usb488_dev_cap & USB488_DEV_CAP_SR1 ? "SR1" : "SR0",
409 uscpi->usb488_dev_cap & USB488_DEV_CAP_RL1 ? "RL1" : "RL0",
410 uscpi->usb488_dev_cap & USB488_DEV_CAP_DT1 ? "DT1" : "DT0");
412 scpi_usbtmc_remote(uscpi);
417 static int scpi_usbtmc_libusb_connection_id(struct sr_scpi_dev_inst *scpi,
418 char **connection_id)
420 struct scpi_usbtmc_libusb *uscpi = scpi->priv;
421 struct sr_usb_dev_inst *usb = uscpi->usb;
423 *connection_id = g_strdup_printf("%s/%" PRIu8 ".%" PRIu8 "",
424 scpi->prefix, usb->bus, usb->address);
429 static int scpi_usbtmc_libusb_source_add(struct sr_session *session,
430 void *priv, int events, int timeout, sr_receive_data_callback cb,
433 struct scpi_usbtmc_libusb *uscpi = priv;
435 return usb_source_add(session, uscpi->ctx, timeout, cb, cb_data);
438 static int scpi_usbtmc_libusb_source_remove(struct sr_session *session,
441 struct scpi_usbtmc_libusb *uscpi = priv;
442 return usb_source_remove(session, uscpi->ctx);
445 static void usbtmc_bulk_out_header_write(void *header, uint8_t MsgID,
447 uint32_t TransferSize,
448 uint8_t bmTransferAttributes,
451 W8(header + 0, MsgID);
452 W8(header + 1, bTag);
453 W8(header + 2, ~bTag);
455 WL32(header + 4, TransferSize);
456 W8(header + 8, bmTransferAttributes);
457 W8(header + 9, TermChar);
458 WL16(header + 10, 0);
461 static int usbtmc_bulk_in_header_read(void *header, uint8_t MsgID,
463 int32_t *TransferSize,
464 uint8_t *bmTransferAttributes)
466 if (R8(header + 0) != MsgID ||
467 R8(header + 1) != bTag ||
468 R8(header + 2) != (unsigned char)~bTag)
471 *TransferSize = RL32(header + 4);
472 if (bmTransferAttributes)
473 *bmTransferAttributes = R8(header + 8);
478 static int scpi_usbtmc_bulkout(struct scpi_usbtmc_libusb *uscpi,
479 uint8_t msg_id, const void *data, int32_t size,
480 uint8_t transfer_attributes)
482 struct sr_usb_dev_inst *usb = uscpi->usb;
483 int padded_size, ret, transferred;
485 if (data && (size + USBTMC_BULK_HEADER_SIZE + 3) > (int)sizeof(uscpi->buffer)) {
486 sr_err("USBTMC bulk out transfer is too big.");
491 uscpi->bTag += !uscpi->bTag; /* bTag == 0 is invalid so avoid it. */
493 usbtmc_bulk_out_header_write(uscpi->buffer, msg_id, uscpi->bTag,
494 size, transfer_attributes, 0);
496 memcpy(uscpi->buffer + USBTMC_BULK_HEADER_SIZE, data, size);
499 size += USBTMC_BULK_HEADER_SIZE;
500 padded_size = (size + 3) & ~0x3;
501 memset(uscpi->buffer + size, 0, padded_size - size);
503 ret = libusb_bulk_transfer(usb->devhdl, uscpi->bulk_out_ep,
504 uscpi->buffer, padded_size, &transferred,
507 sr_err("USBTMC bulk out transfer error: %s.",
508 libusb_error_name(ret));
512 if (transferred < padded_size) {
513 sr_dbg("USBTMC bulk out partial transfer (%d/%d bytes).",
514 transferred, padded_size);
518 return transferred - USBTMC_BULK_HEADER_SIZE;
521 static int scpi_usbtmc_bulkin_start(struct scpi_usbtmc_libusb *uscpi,
522 uint8_t msg_id, void *data, int32_t size,
523 uint8_t *transfer_attributes)
525 struct sr_usb_dev_inst *usb = uscpi->usb;
526 int ret, transferred, message_size;
528 ret = libusb_bulk_transfer(usb->devhdl, uscpi->bulk_in_ep, data, size,
529 &transferred, TRANSFER_TIMEOUT);
531 sr_err("USBTMC bulk in transfer error: %s.",
532 libusb_error_name(ret));
536 if (usbtmc_bulk_in_header_read(data, msg_id, uscpi->bTag, &message_size,
537 transfer_attributes) != SR_OK) {
538 sr_err("USBTMC invalid bulk in header.");
542 message_size += USBTMC_BULK_HEADER_SIZE;
543 uscpi->response_length = MIN(transferred, message_size);
544 uscpi->response_bytes_read = USBTMC_BULK_HEADER_SIZE;
545 uscpi->remaining_length = message_size - uscpi->response_length;
547 return transferred - USBTMC_BULK_HEADER_SIZE;
550 static int scpi_usbtmc_bulkin_continue(struct scpi_usbtmc_libusb *uscpi,
551 void *data, int size)
553 struct sr_usb_dev_inst *usb = uscpi->usb;
554 int ret, transferred;
556 ret = libusb_bulk_transfer(usb->devhdl, uscpi->bulk_in_ep, data, size,
557 &transferred, TRANSFER_TIMEOUT);
559 sr_err("USBTMC bulk in transfer error: %s.",
560 libusb_error_name(ret));
564 uscpi->response_length = MIN(transferred, uscpi->remaining_length);
565 uscpi->response_bytes_read = 0;
566 uscpi->remaining_length -= uscpi->response_length;
571 static int scpi_usbtmc_libusb_send(void *priv, const char *command)
573 struct scpi_usbtmc_libusb *uscpi = priv;
575 if (scpi_usbtmc_bulkout(uscpi, DEV_DEP_MSG_OUT,
576 command, strlen(command), EOM) <= 0)
579 sr_spew("Successfully sent SCPI command: '%s'.", command);
584 static int scpi_usbtmc_libusb_read_begin(void *priv)
586 struct scpi_usbtmc_libusb *uscpi = priv;
588 uscpi->remaining_length = 0;
590 if (scpi_usbtmc_bulkout(uscpi, REQUEST_DEV_DEP_MSG_IN,
591 NULL, INT32_MAX, 0) < 0)
593 if (scpi_usbtmc_bulkin_start(uscpi, DEV_DEP_MSG_IN,
594 uscpi->buffer, sizeof(uscpi->buffer),
595 &uscpi->bulkin_attributes) < 0)
601 static int scpi_usbtmc_libusb_read_data(void *priv, char *buf, int maxlen)
603 struct scpi_usbtmc_libusb *uscpi = priv;
606 if (uscpi->response_bytes_read >= uscpi->response_length) {
607 if (uscpi->remaining_length > 0) {
608 if (scpi_usbtmc_bulkin_continue(uscpi, uscpi->buffer,
609 sizeof(uscpi->buffer)) <= 0)
612 if (uscpi->bulkin_attributes & EOM)
614 if (scpi_usbtmc_libusb_read_begin(uscpi) < 0)
619 read_length = MIN(uscpi->response_length - uscpi->response_bytes_read, maxlen);
621 memcpy(buf, uscpi->buffer + uscpi->response_bytes_read, read_length);
623 uscpi->response_bytes_read += read_length;
628 static int scpi_usbtmc_libusb_read_complete(void *priv)
630 struct scpi_usbtmc_libusb *uscpi = priv;
631 return uscpi->response_bytes_read >= uscpi->response_length &&
632 uscpi->remaining_length <= 0 &&
633 uscpi->bulkin_attributes & EOM;
636 static int scpi_usbtmc_libusb_close(struct sr_scpi_dev_inst *scpi)
638 struct scpi_usbtmc_libusb *uscpi = scpi->priv;
639 struct sr_usb_dev_inst *usb = uscpi->usb;
645 scpi_usbtmc_local(uscpi);
647 if ((ret = libusb_release_interface(usb->devhdl, uscpi->interface)) < 0)
648 sr_err("Failed to release interface: %s.",
649 libusb_error_name(ret));
651 if (uscpi->detached_kernel_driver) {
652 if ((ret = libusb_attach_kernel_driver(usb->devhdl,
653 uscpi->interface)) < 0)
654 sr_err("Failed to re-attach kernel driver: %s.",
655 libusb_error_name(ret));
657 uscpi->detached_kernel_driver = 0;
664 static void scpi_usbtmc_libusb_free(void *priv)
666 struct scpi_usbtmc_libusb *uscpi = priv;
667 sr_usb_dev_inst_free(uscpi->usb);
670 SR_PRIV const struct sr_scpi_dev_inst scpi_usbtmc_libusb_dev = {
673 .transport = SCPI_TRANSPORT_USBTMC,
674 .priv_size = sizeof(struct scpi_usbtmc_libusb),
675 .scan = scpi_usbtmc_libusb_scan,
676 .dev_inst_new = scpi_usbtmc_libusb_dev_inst_new,
677 .open = scpi_usbtmc_libusb_open,
678 .connection_id = scpi_usbtmc_libusb_connection_id,
679 .source_add = scpi_usbtmc_libusb_source_add,
680 .source_remove = scpi_usbtmc_libusb_source_remove,
681 .send = scpi_usbtmc_libusb_send,
682 .read_begin = scpi_usbtmc_libusb_read_begin,
683 .read_data = scpi_usbtmc_libusb_read_data,
684 .read_complete = scpi_usbtmc_libusb_read_complete,
685 .close = scpi_usbtmc_libusb_close,
686 .free = scpi_usbtmc_libusb_free,