openocd/src/jtag/drivers/mpsse.c

/**************************************************************************
 *   Copyright (C) 2012 by Andreas Fritiofson                              *
 *   andreas.fritiofson@gmail.com                                          *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
 *   GNU General Public License for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the                         *
 *   Free Software Foundation, Inc.,                                       *
 *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
 ***************************************************************************/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "mpsse.h"
#include "helper/log.h"
#include <libusb-1.0/libusb.h>

/* Compatibility define for older libusb-1.0 */
#ifndef LIBUSB_CALL
#define LIBUSB_CALL
#endif

#ifdef _DEBUG_JTAG_IO_
#define DEBUG_IO(expr...) LOG_DEBUG(expr)
#define DEBUG_PRINT_BUF(buf, len) \
	do { \
		char buf_string[32 * 3 + 1]; \
		int buf_string_pos = 0; \
		for (int i = 0; i < len; i++) { \
			buf_string_pos += sprintf(buf_string + buf_string_pos, " %02x", buf[i]); \
			if (i % 32 == 32 - 1) { \
				LOG_DEBUG("%s", buf_string); \
				buf_string_pos = 0; \
			} \
		} \
		if (buf_string_pos > 0) \
			LOG_DEBUG("%s", buf_string);\
	} while (0)
#else
#define DEBUG_IO(expr...) do {} while (0)
#define DEBUG_PRINT_BUF(buf, len) do {} while (0)
#endif

#define FTDI_DEVICE_OUT_REQTYPE (LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_RECIPIENT_DEVICE)
#define FTDI_DEVICE_IN_REQTYPE (0x80 | LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_RECIPIENT_DEVICE)

#define BITMODE_MPSSE 0x02

#define SIO_RESET_REQUEST             0x00
#define SIO_SET_LATENCY_TIMER_REQUEST 0x09
#define SIO_GET_LATENCY_TIMER_REQUEST 0x0A
#define SIO_SET_BITMODE_REQUEST       0x0B

#define SIO_RESET_SIO 0
#define SIO_RESET_PURGE_RX 1
#define SIO_RESET_PURGE_TX 2

struct mpsse_ctx {
	libusb_context *usb_ctx;
	libusb_device_handle *usb_dev;
	unsigned int usb_write_timeout;
	unsigned int usb_read_timeout;
	uint8_t in_ep;
	uint8_t out_ep;
	uint16_t max_packet_size;
	uint16_t index;
	uint8_t interface;
	enum ftdi_chip_type type;
	uint8_t *write_buffer;
	unsigned write_size;
	unsigned write_count;
	uint8_t *read_buffer;
	unsigned read_size;
	unsigned read_count;
	uint8_t *read_chunk;
	unsigned read_chunk_size;
	struct bit_copy_queue read_queue;
};

/* Returns true if the string descriptor indexed by str_index in device matches string */
static bool string_descriptor_equal(libusb_device_handle *device, uint8_t str_index,
	const char *string)
{
	int retval;
	char desc_string[256]; /* Max size of string descriptor */
	retval = libusb_get_string_descriptor_ascii(device, str_index, (unsigned char *)desc_string,
			sizeof(desc_string));
	if (retval < 0) {
		LOG_ERROR("libusb_get_string_descriptor_ascii() failed with %d", retval);
		return false;
	}
	return strncmp(string, desc_string, sizeof(desc_string)) == 0;
}

/* Helper to open a libusb device that matches vid, pid, product string and/or serial string.
 * Set any field to 0 as a wildcard. If the device is found true is returned, with ctx containing
 * the already opened handle. ctx->interface must be set to the desired interface (channel) number
 * prior to calling this function. */
static bool open_matching_device(struct mpsse_ctx *ctx, const uint16_t *vid, const uint16_t *pid,
	const char *product, const char *serial)
{
	libusb_device **list;
	struct libusb_device_descriptor desc;
	struct libusb_config_descriptor *config0;
	int err;
	bool found = false;
	ssize_t cnt = libusb_get_device_list(ctx->usb_ctx, &list);
	if (cnt < 0)
		LOG_ERROR("libusb_get_device_list() failed with %zi", cnt);

	for (ssize_t i = 0; i < cnt; i++) {
		libusb_device *device = list[i];

		err = libusb_get_device_descriptor(device, &desc);
		if (err != LIBUSB_SUCCESS) {
			LOG_ERROR("libusb_get_device_descriptor() failed with %d", err);
			continue;
		}

		if (vid && *vid != desc.idVendor)
			continue;
		if (pid && *pid != desc.idProduct)
			continue;

		err = libusb_open(device, &ctx->usb_dev);
		if (err != LIBUSB_SUCCESS) {
			LOG_ERROR("libusb_open() failed with %d", err);
			continue;
		}

		if (product && !string_descriptor_equal(ctx->usb_dev, desc.iProduct, product)) {
			libusb_close(ctx->usb_dev);
			continue;
		}

		if (serial && !string_descriptor_equal(ctx->usb_dev, desc.iSerialNumber, serial)) {
			libusb_close(ctx->usb_dev);
			continue;
		}

		found = true;
		break;
	}

	libusb_free_device_list(list, 1);

	if (!found) {
		LOG_ERROR("no device found");
		return false;
	}

	err = libusb_get_config_descriptor(libusb_get_device(ctx->usb_dev), 0, &config0);
	if (err != LIBUSB_SUCCESS) {
		LOG_ERROR("libusb_get_config_descriptor() failed with %d", err);
		libusb_close(ctx->usb_dev);
		return false;
	}

	/* Make sure the first configuration is selected */
	int cfg;
	err = libusb_get_configuration(ctx->usb_dev, &cfg);
	if (err != LIBUSB_SUCCESS) {
		LOG_ERROR("libusb_get_configuration() failed with %d", err);
		goto error;
	}

	if (desc.bNumConfigurations > 0 && cfg != config0->bConfigurationValue) {
		err = libusb_set_configuration(ctx->usb_dev, config0->bConfigurationValue);
		if (err != LIBUSB_SUCCESS) {
			LOG_ERROR("libusb_set_configuration() failed with %d", err);
			goto error;
		}
	}

	/* Try to detach ftdi_sio kernel module */
	err = libusb_detach_kernel_driver(ctx->usb_dev, ctx->interface);
	if (err != LIBUSB_SUCCESS && err != LIBUSB_ERROR_NOT_FOUND
			&& err != LIBUSB_ERROR_NOT_SUPPORTED) {
		LOG_ERROR("libusb_detach_kernel_driver() failed with %d", err);
		goto error;
	}

	err = libusb_claim_interface(ctx->usb_dev, ctx->interface);
	if (err != LIBUSB_SUCCESS) {
		LOG_ERROR("libusb_claim_interface() failed with %d", err);
		goto error;
	}

	/* Reset FTDI device */
	err = libusb_control_transfer(ctx->usb_dev, FTDI_DEVICE_OUT_REQTYPE,
			SIO_RESET_REQUEST, SIO_RESET_SIO,
			ctx->index, NULL, 0, ctx->usb_write_timeout);
	if (err < 0) {
		LOG_ERROR("failed to reset FTDI device: %d", err);
		goto error;
	}

	switch (desc.bcdDevice) {
	case 0x500:
		ctx->type = TYPE_FT2232C;
		break;
	case 0x700:
		ctx->type = TYPE_FT2232H;
		break;
	case 0x800:
		ctx->type = TYPE_FT4232H;
		break;
	case 0x900:
		ctx->type = TYPE_FT232H;
		break;
	default:
		LOG_ERROR("unsupported FTDI chip type: 0x%04x", desc.bcdDevice);
		goto error;
	}

	/* Determine maximum packet size and endpoint addresses */
	if (!(desc.bNumConfigurations > 0 && ctx->interface < config0->bNumInterfaces
			&& config0->interface[ctx->interface].num_altsetting > 0))
		goto desc_error;

	const struct libusb_interface_descriptor *descriptor;
	descriptor = &config0->interface[ctx->interface].altsetting[0];
	if (descriptor->bNumEndpoints != 2)
		goto desc_error;

	ctx->in_ep = 0;
	ctx->out_ep = 0;
	for (int i = 0; i < descriptor->bNumEndpoints; i++) {
		if (descriptor->endpoint[i].bEndpointAddress & 0x80) {
			ctx->in_ep = descriptor->endpoint[i].bEndpointAddress;
			ctx->max_packet_size =
					descriptor->endpoint[i].wMaxPacketSize;
		} else {
			ctx->out_ep = descriptor->endpoint[i].bEndpointAddress;
		}
	}

	if (ctx->in_ep == 0 || ctx->out_ep == 0)
		goto desc_error;

	libusb_free_config_descriptor(config0);
	return true;

desc_error:
	LOG_ERROR("unrecognized USB device descriptor");
error:
	libusb_free_config_descriptor(config0);
	libusb_close(ctx->usb_dev);
	return false;
}

struct mpsse_ctx *mpsse_open(const uint16_t *vid, const uint16_t *pid, const char *description,
	const char *serial, int channel)
{
	struct mpsse_ctx *ctx = calloc(1, sizeof(*ctx));
	int err;

	if (!ctx)
		return 0;

	bit_copy_queue_init(&ctx->read_queue);
	ctx->read_chunk_size = 16384;
	ctx->read_size = 16384;
	ctx->write_size = 16384;
	ctx->read_chunk = malloc(ctx->read_chunk_size);
	ctx->read_buffer = malloc(ctx->read_size);
	ctx->write_buffer = malloc(ctx->write_size);
	if (!ctx->read_chunk || !ctx->read_buffer || !ctx->write_buffer)
		goto error;

	ctx->interface = channel;
	ctx->index = channel + 1;
	ctx->usb_read_timeout = 5000;
	ctx->usb_write_timeout = 5000;

	err = libusb_init(&ctx->usb_ctx);
	if (err != LIBUSB_SUCCESS) {
		LOG_ERROR("libusb_init() failed with %d", err);
		goto error;
	}

	if (!open_matching_device(ctx, vid, pid, description, serial)) {
		/* Four hex digits plus terminating zero each */
		char vidstr[5];
		char pidstr[5];
		LOG_ERROR("unable to open ftdi device with vid %s, pid %s, description '%s' and "
				"serial '%s'",
				vid ? sprintf(vidstr, "%04x", *vid), vidstr : "*",
				pid ? sprintf(pidstr, "%04x", *pid), pidstr : "*",
				description ? description : "*",
				serial ? serial : "*");
		ctx->usb_dev = 0;
		goto error;
	}

	err = libusb_control_transfer(ctx->usb_dev, FTDI_DEVICE_OUT_REQTYPE,
			SIO_SET_LATENCY_TIMER_REQUEST, 255, ctx->index, NULL, 0,
			ctx->usb_write_timeout);
	if (err < 0) {
		LOG_ERROR("unable to set latency timer: %d", err);
		goto error;
	}

	err = libusb_control_transfer(ctx->usb_dev,
			FTDI_DEVICE_OUT_REQTYPE,
			SIO_SET_BITMODE_REQUEST,
			0x0b | (BITMODE_MPSSE << 8),
			ctx->index,
			NULL,
			0,
			ctx->usb_write_timeout);
	if (err < 0) {
		LOG_ERROR("unable to set MPSSE bitmode: %d", err);
		goto error;
	}

	mpsse_purge(ctx);

	return ctx;
error:
	mpsse_close(ctx);
	return 0;
}

void mpsse_close(struct mpsse_ctx *ctx)
{
	if (ctx->usb_dev)
		libusb_close(ctx->usb_dev);
	if (ctx->usb_ctx)
		libusb_exit(ctx->usb_ctx);
	bit_copy_discard(&ctx->read_queue);
	if (ctx->write_buffer)
		free(ctx->write_buffer);
	if (ctx->read_buffer)
		free(ctx->read_buffer);
	if (ctx->read_chunk)
		free(ctx->read_chunk);

	free(ctx);
}

bool mpsse_is_high_speed(struct mpsse_ctx *ctx)
{
	return ctx->type != TYPE_FT2232C;
}

void mpsse_purge(struct mpsse_ctx *ctx)
{
	int err;
	LOG_DEBUG("-");
	ctx->write_count = 0;
	ctx->read_count = 0;
	bit_copy_discard(&ctx->read_queue);
	err = libusb_control_transfer(ctx->usb_dev, FTDI_DEVICE_OUT_REQTYPE, SIO_RESET_REQUEST,
			SIO_RESET_PURGE_RX, ctx->index, NULL, 0, ctx->usb_write_timeout);
	if (err < 0) {
		LOG_ERROR("unable to purge ftdi rx buffers: %d", err);
		return;
	}

	err = libusb_control_transfer(ctx->usb_dev, FTDI_DEVICE_OUT_REQTYPE, SIO_RESET_REQUEST,
			SIO_RESET_PURGE_TX, ctx->index, NULL, 0, ctx->usb_write_timeout);
	if (err < 0) {
		LOG_ERROR("unable to purge ftdi tx buffers: %d", err);
		return;
	}
}

static unsigned buffer_write_space(struct mpsse_ctx *ctx)
{
	/* Reserve one byte for SEND_IMMEDIATE */
	return ctx->write_size - ctx->write_count - 1;
}

static unsigned buffer_read_space(struct mpsse_ctx *ctx)
{
	return ctx->read_size - ctx->read_count;
}

static void buffer_write_byte(struct mpsse_ctx *ctx, uint8_t data)
{
	DEBUG_IO("%02x", data);
	assert(ctx->write_count < ctx->write_size);
	ctx->write_buffer[ctx->write_count++] = data;
}

static unsigned buffer_write(struct mpsse_ctx *ctx, const uint8_t *out, unsigned out_offset,
	unsigned bit_count)
{
	DEBUG_IO("%d bits", bit_count);
	assert(ctx->write_count + DIV_ROUND_UP(bit_count, 8) <= ctx->write_size);
	bit_copy(ctx->write_buffer + ctx->write_count, 0, out, out_offset, bit_count);
	ctx->write_count += DIV_ROUND_UP(bit_count, 8);
	return bit_count;
}

static unsigned buffer_add_read(struct mpsse_ctx *ctx, uint8_t *in, unsigned in_offset,
	unsigned bit_count, unsigned offset)
{
	DEBUG_IO("%d bits, offset %d", bit_count, offset);
	assert(ctx->read_count + DIV_ROUND_UP(bit_count, 8) <= ctx->read_size);
	bit_copy_queued(&ctx->read_queue, in, in_offset, ctx->read_buffer + ctx->read_count, offset,
		bit_count);
	ctx->read_count += DIV_ROUND_UP(bit_count, 8);
	return bit_count;
}

int mpsse_clock_data_out(struct mpsse_ctx *ctx, const uint8_t *out, unsigned out_offset,
	unsigned length, uint8_t mode)
{
	return mpsse_clock_data(ctx, out, out_offset, 0, 0, length, mode);
}

int mpsse_clock_data_in(struct mpsse_ctx *ctx, uint8_t *in, unsigned in_offset, unsigned length,
	uint8_t mode)
{
	return mpsse_clock_data(ctx, 0, 0, in, in_offset, length, mode);
}

int mpsse_clock_data(struct mpsse_ctx *ctx, const uint8_t *out, unsigned out_offset, uint8_t *in,
	unsigned in_offset, unsigned length, uint8_t mode)
{
	/* TODO: Fix MSB first modes */
	DEBUG_IO("%s%s %d bits", in ? "in" : "", out ? "out" : "", length);
	int retval = ERROR_OK;

	/* TODO: On H chips, use command 0x8E/0x8F if in and out are both 0 */
	if (out || (!out && !in))
		mode |= 0x10;
	if (in)
		mode |= 0x20;

	while (length > 0) {
		/* Guarantee buffer space enough for a minimum size transfer */
		if (buffer_write_space(ctx) + (length < 8) < (out || (!out && !in) ? 4 : 3)
				|| (in && buffer_read_space(ctx) < 1))
			retval = mpsse_flush(ctx);

		if (length < 8) {
			/* Transfer remaining bits in bit mode */
			buffer_write_byte(ctx, 0x02 | mode);
			buffer_write_byte(ctx, length - 1);
			if (out)
				out_offset += buffer_write(ctx, out, out_offset, length);
			if (in)
				in_offset += buffer_add_read(ctx, in, in_offset, length, 8 - length);
			if (!out && !in)
				buffer_write_byte(ctx, 0x00);
			length = 0;
		} else {
			/* Byte transfer */
			unsigned this_bytes = length / 8;
			/* MPSSE command limit */
			if (this_bytes > 65536)
				this_bytes = 65536;
			/* Buffer space limit. We already made sure there's space for the minimum
			 * transfer. */
			if ((out || (!out && !in)) && this_bytes + 3 > buffer_write_space(ctx))
				this_bytes = buffer_write_space(ctx) - 3;
			if (in && this_bytes > buffer_read_space(ctx))
				this_bytes = buffer_read_space(ctx);

			if (this_bytes > 0) {
				buffer_write_byte(ctx, mode);
				buffer_write_byte(ctx, (this_bytes - 1) & 0xff);
				buffer_write_byte(ctx, (this_bytes - 1) >> 8);
				if (out)
					out_offset += buffer_write(ctx,
							out,
							out_offset,
							this_bytes * 8);
				if (in)
					in_offset += buffer_add_read(ctx,
							in,
							in_offset,
							this_bytes * 8,
							0);
				if (!out && !in)
					for (unsigned n = 0; n < this_bytes; n++)
						buffer_write_byte(ctx, 0x00);
				length -= this_bytes * 8;
			}
		}
	}
	return retval;
}

int mpsse_clock_tms_cs_out(struct mpsse_ctx *ctx, const uint8_t *out, unsigned out_offset,
	unsigned length, bool tdi, uint8_t mode)
{
	return mpsse_clock_tms_cs(ctx, out, out_offset, 0, 0, length, tdi, mode);
}

int mpsse_clock_tms_cs(struct mpsse_ctx *ctx, const uint8_t *out, unsigned out_offset, uint8_t *in,
	unsigned in_offset, unsigned length, bool tdi, uint8_t mode)
{
	DEBUG_IO("%sout %d bits, tdi=%d", in ? "in" : "", length, tdi);
	assert(out);
	int retval = ERROR_OK;

	mode |= 0x42;
	if (in)
		mode |= 0x20;

	while (length > 0) {
		/* Guarantee buffer space enough for a minimum size transfer */
		if (buffer_write_space(ctx) < 3 || (in && buffer_read_space(ctx) < 1))
			retval = mpsse_flush(ctx);

		/* Byte transfer */
		unsigned this_bits = length;
		/* MPSSE command limit */
		/* NOTE: there's a report of an FT2232 bug in this area, where shifting
		 * exactly 7 bits can make problems with TMS signaling for the last
		 * clock cycle:
		 *
		 * http://developer.intra2net.com/mailarchive/html/libftdi/2009/msg00292.html
		 */
		if (this_bits > 7)
			this_bits = 7;

		if (this_bits > 0) {
			buffer_write_byte(ctx, mode);
			buffer_write_byte(ctx, this_bits - 1);
			uint8_t data = 0;
			/* TODO: Fix MSB first, if allowed in MPSSE */
			bit_copy(&data, 0, out, out_offset, this_bits);
			out_offset += this_bits;
			buffer_write_byte(ctx, data | (tdi ? 0x80 : 0x00));
			if (in)
				in_offset += buffer_add_read(ctx,
						in,
						in_offset,
						this_bits,
						8 - this_bits);
			length -= this_bits;
		}
	}
	return retval;
}

int mpsse_set_data_bits_low_byte(struct mpsse_ctx *ctx, uint8_t data, uint8_t dir)
{
	DEBUG_IO("-");
	int retval = ERROR_OK;

	if (buffer_write_space(ctx) < 3)
		retval = mpsse_flush(ctx);

	buffer_write_byte(ctx, 0x80);
	buffer_write_byte(ctx, data);
	buffer_write_byte(ctx, dir);

	return retval;
}

int mpsse_set_data_bits_high_byte(struct mpsse_ctx *ctx, uint8_t data, uint8_t dir)
{
	DEBUG_IO("-");
	int retval = ERROR_OK;

	if (buffer_write_space(ctx) < 3)
		retval = mpsse_flush(ctx);

	buffer_write_byte(ctx, 0x82);
	buffer_write_byte(ctx, data);
	buffer_write_byte(ctx, dir);

	return retval;
}

int mpsse_read_data_bits_low_byte(struct mpsse_ctx *ctx, uint8_t *data)
{
	DEBUG_IO("-");
	int retval = ERROR_OK;

	if (buffer_write_space(ctx) < 1)
		retval = mpsse_flush(ctx);

	buffer_write_byte(ctx, 0x81);
	buffer_add_read(ctx, data, 0, 8, 0);

	return retval;
}

int mpsse_read_data_bits_high_byte(struct mpsse_ctx *ctx, uint8_t *data)
{
	DEBUG_IO("-");
	int retval = ERROR_OK;

	if (buffer_write_space(ctx) < 1)
		retval = mpsse_flush(ctx);

	buffer_write_byte(ctx, 0x83);
	buffer_add_read(ctx, data, 0, 8, 0);

	return retval;
}

static int single_byte_boolean_helper(struct mpsse_ctx *ctx, bool var, uint8_t val_if_true,
	uint8_t val_if_false)
{
	int retval = ERROR_OK;

	if (buffer_write_space(ctx) < 1)
		retval = mpsse_flush(ctx);

	buffer_write_byte(ctx, var ? val_if_true : val_if_false);

	return retval;
}

int mpsse_loopback_config(struct mpsse_ctx *ctx, bool enable)
{
	LOG_DEBUG("%s", enable ? "on" : "off");
	return single_byte_boolean_helper(ctx, enable, 0x84, 0x85);
}

int mpsse_set_divisor(struct mpsse_ctx *ctx, uint16_t divisor)
{
	LOG_DEBUG("%d", divisor);
	int retval = ERROR_OK;

	if (buffer_write_space(ctx) < 3)
		retval = mpsse_flush(ctx);

	buffer_write_byte(ctx, 0x86);
	buffer_write_byte(ctx, divisor & 0xff);
	buffer_write_byte(ctx, divisor >> 8);

	return retval;
}

int mpsse_divide_by_5_config(struct mpsse_ctx *ctx, bool enable)
{
	if (!mpsse_is_high_speed(ctx))
		return ERROR_FAIL;

	LOG_DEBUG("%s", enable ? "on" : "off");

	return single_byte_boolean_helper(ctx, enable, 0x8b, 0x8a);
}

int mpsse_rtck_config(struct mpsse_ctx *ctx, bool enable)
{
	if (!mpsse_is_high_speed(ctx))
		return ERROR_FAIL;

	LOG_DEBUG("%s", enable ? "on" : "off");

	return single_byte_boolean_helper(ctx, enable, 0x96, 0x97);
}

int mpsse_set_frequency(struct mpsse_ctx *ctx, int frequency)
{
	LOG_DEBUG("target %d Hz", frequency);
	assert(frequency >= 0);
	int base_clock;

	if (frequency == 0)
		return mpsse_rtck_config(ctx, true);

	mpsse_rtck_config(ctx, false); /* just try */

	if (frequency > 60000000 / 2 / 65536 && mpsse_is_high_speed(ctx)) {
		int retval = mpsse_divide_by_5_config(ctx, false);
		if (retval != ERROR_OK)
			return retval;
		base_clock = 60000000;
	} else {
		mpsse_divide_by_5_config(ctx, true); /* just try */
		base_clock = 12000000;
	}

	int divisor = (base_clock / 2 + frequency - 1) / frequency - 1;
	if (divisor > 65535)
		divisor = 65535;
	assert(divisor >= 0);

	int retval = mpsse_set_divisor(ctx, divisor);
	if (retval != ERROR_OK)
		return retval;

	frequency = base_clock / 2 / (1 + divisor);
	LOG_DEBUG("actually %d Hz", frequency);

	return frequency;
}

/* Context needed by the callbacks */
struct transfer_result {
	struct mpsse_ctx *ctx;
	bool done;
	unsigned transferred;
};

static LIBUSB_CALL void read_cb(struct libusb_transfer *transfer)
{
	struct transfer_result *res = (struct transfer_result *)transfer->user_data;
	struct mpsse_ctx *ctx = res->ctx;

	unsigned packet_size = ctx->max_packet_size;

	DEBUG_PRINT_BUF(transfer->buffer, transfer->actual_length);

	/* Strip the two status bytes sent at the beginning of each USB packet
	 * while copying the chunk buffer to the read buffer */
	unsigned num_packets = DIV_ROUND_UP(transfer->actual_length, packet_size);
	unsigned chunk_remains = transfer->actual_length;
	for (unsigned i = 0; i < num_packets && chunk_remains > 2; i++) {
		unsigned this_size = packet_size - 2;
		if (this_size > chunk_remains - 2)
			this_size = chunk_remains - 2;
		if (this_size > ctx->read_count - res->transferred)
			this_size = ctx->read_count - res->transferred;
		memcpy(ctx->read_buffer + res->transferred,
			ctx->read_chunk + packet_size * i + 2,
			this_size);
		res->transferred += this_size;
		chunk_remains -= this_size + 2;
		if (res->transferred == ctx->read_count) {
			res->done = true;
			break;
		}
	}

	DEBUG_IO("raw chunk %d, transferred %d of %d", transfer->actual_length, res->transferred,
		ctx->read_count);

	if (!res->done)
		if (libusb_submit_transfer(transfer) != LIBUSB_SUCCESS)
			res->done = true;
}

static LIBUSB_CALL void write_cb(struct libusb_transfer *transfer)
{
	struct transfer_result *res = (struct transfer_result *)transfer->user_data;
	struct mpsse_ctx *ctx = res->ctx;

	res->transferred += transfer->actual_length;

	DEBUG_IO("transferred %d of %d", res->transferred, ctx->write_count);

	DEBUG_PRINT_BUF(transfer->buffer, transfer->actual_length);

	if (res->transferred == ctx->write_count)
		res->done = true;
	else {
		transfer->length = ctx->write_count - res->transferred;
		transfer->buffer = ctx->write_buffer + res->transferred;
		if (libusb_submit_transfer(transfer) != LIBUSB_SUCCESS)
			res->done = true;
	}
}

int mpsse_flush(struct mpsse_ctx *ctx)
{
	DEBUG_IO("write %d%s, read %d", ctx->write_count, ctx->read_count ? "+1" : "",
			ctx->read_count);
	assert(ctx->write_count > 0 || ctx->read_count == 0); /* No read data without write data */
	int retval = ERROR_OK;

	if (ctx->write_count == 0)
		return retval;

	struct libusb_transfer *read_transfer = 0;
	struct transfer_result read_result = { .ctx = ctx, .done = true };
	if (ctx->read_count) {
		buffer_write_byte(ctx, 0x87); /* SEND_IMMEDIATE */
		read_result.done = false;
		/* delay read transaction to ensure the FTDI chip can support us with data
		   immediately after processing the MPSSE commands in the write transaction */
	}

	struct transfer_result write_result = { .ctx = ctx, .done = false };
	struct libusb_transfer *write_transfer = libusb_alloc_transfer(0);
	libusb_fill_bulk_transfer(write_transfer, ctx->usb_dev, ctx->out_ep, ctx->write_buffer,
		ctx->write_count, write_cb, &write_result, ctx->usb_write_timeout);
	retval = libusb_submit_transfer(write_transfer);

	if (ctx->read_count) {
		read_transfer = libusb_alloc_transfer(0);
		libusb_fill_bulk_transfer(read_transfer, ctx->usb_dev, ctx->in_ep, ctx->read_chunk,
			ctx->read_chunk_size, read_cb, &read_result,
			ctx->usb_read_timeout);
		retval = libusb_submit_transfer(read_transfer);
	}

	/* Polling loop, more or less taken from libftdi */
	while (!write_result.done || !read_result.done) {
		retval = libusb_handle_events(ctx->usb_ctx);
		keep_alive();
		if (retval != LIBUSB_SUCCESS && retval != LIBUSB_ERROR_INTERRUPTED) {
			libusb_cancel_transfer(write_transfer);
			if (read_transfer)
				libusb_cancel_transfer(read_transfer);
			while (!write_result.done || !read_result.done)
				if (libusb_handle_events(ctx->usb_ctx) != LIBUSB_SUCCESS)
					break;
		}
	}

	if (retval != LIBUSB_SUCCESS) {
		LOG_ERROR("libusb_handle_events() failed with %d", retval);
		retval = ERROR_FAIL;
	} else if (write_result.transferred < ctx->write_count) {
		LOG_ERROR("ftdi device did not accept all data: %d, tried %d",
			write_result.transferred,
			ctx->write_count);
		retval = ERROR_FAIL;
	} else if (read_result.transferred < ctx->read_count) {
		LOG_ERROR("ftdi device did not return all data: %d, expected %d",
			read_result.transferred,
			ctx->read_count);
		retval = ERROR_FAIL;
	} else if (ctx->read_count) {
		ctx->write_count = 0;
		ctx->read_count = 0;
		bit_copy_execute(&ctx->read_queue);
		retval = ERROR_OK;
	} else {
		ctx->write_count = 0;
		bit_copy_discard(&ctx->read_queue);
		retval = ERROR_OK;
	}

	libusb_free_transfer(write_transfer);
	if (read_transfer)
		libusb_free_transfer(read_transfer);

	if (retval != ERROR_OK)
		mpsse_purge(ctx);

	return retval;
}