drivers/jtag: rewrite usb_blaster driver

[openocd.git] / src / jtag / drivers / usb_blaster / usb_blaster.c

/*
 *   Driver for USB-JTAG, Altera USB-Blaster and compatibles
 *
 *   Inspired from original code from Kolja Waschk's USB-JTAG project
 *   (http://www.ixo.de/info/usb_jtag/), and from openocd project.
 *
 *   Copyright (C) 2012 Robert Jarzmik robert.jarzmik@free.fr
 *   Copyright (C) 2011 Ali Lown ali@lown.me.uk
 *   Copyright (C) 2009 Catalin Patulea cat@vv.carleton.ca
 *   Copyright (C) 2006 Kolja Waschk usbjtag@ixo.de
 *
 *   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.
 *
 */

/*
 * The following information is originally from Kolja Waschk's USB-JTAG,
 * where it was obtained by reverse engineering an Altera USB-Blaster.
 * See http://www.ixo.de/info/usb_jtag/ for USB-Blaster block diagram and
 * usb_jtag-20080705-1200.zip#usb_jtag/host/openocd for protocol.
 *
 * The same information is also on the UrJTAG mediawiki, with some additional
 * notes on bits marked as "unknown" by usb_jtag.
 * (http://sourceforge.net/apps/mediawiki/urjtag/index.php?
 *    title=Cable_Altera_USB-Blaster)
 *
 * USB-JTAG, Altera USB-Blaster and compatibles are typically implemented as
 * an FTDIChip FT245 followed by a CPLD which handles a two-mode protocol:
 *
 *            _________
 *           |         |
 *           | AT93C46 |
 *           |_________|
 *            __|__________    _________
 *           |             |  |         |
 *      USB__| FTDI 245BM  |__| EPM7064 |__JTAG (B_TDO,B_TDI,B_TMS,B_TCK)
 *           |_____________|  |_________|
 *            __|__________    _|___________
 *           |             |  |             |
 *           | 6 MHz XTAL  |  | 24 MHz Osc. |
 *           |_____________|  |_____________|
 *
 */

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

#if IS_CYGWIN == 1
#include "windows.h"
#undef LOG_ERROR
#endif

/* project specific includes */
#include <jtag/interface.h>
#include <jtag/commands.h>
#include <helper/time_support.h>
#include "ublast_access.h"

/* system includes */
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/time.h>
#include <time.h>

/* Size of USB endpoint max packet size, ie. 64 bytes */
#define MAX_PACKET_SIZE 64
/*
 * Size of data buffer that holds bytes in byte-shift mode.
 * This buffer can hold multiple USB packets aligned to
 * MAX_PACKET_SIZE bytes boundaries.
 * BUF_LEN must be grater than or equal MAX_PACKET_SIZE.
 */
#define BUF_LEN 4096

struct ublast_info {
        int pin6;
        int pin8;
        int tms;
        int tdi;
        uint8_t buf[BUF_LEN];
        int bufidx;

        char *lowlevel_name;
        struct ublast_lowlevel *drv;
        char *ublast_device_desc;
        uint16_t ublast_vid, ublast_pid;
};

/*
 * Global device control
 */
static struct ublast_info info = {
        .ublast_vid = 0x09fb, /* Altera */
        .ublast_pid = 0x6001, /* USB-Blaster */
        .lowlevel_name = NULL,
};

/*
 * Available lowlevel drivers (FTDI, FTD2xx, ...)
 */
struct drvs_map {
        char *name;
        struct ublast_lowlevel *(*drv_register)(void);
};

static struct drvs_map lowlevel_drivers_map[] = {
#if BUILD_USB_BLASTER_LIBFTDI
        { .name = "ftdi", .drv_register = ublast_register_ftdi },
#endif
#if BUILD_USB_BLASTER_FTD2XX
        { .name = "ftd2xx", .drv_register = ublast_register_ftd2xx },
#endif
        { NULL, NULL },
};

/*
 * Access functions to lowlevel driver, agnostic of libftdi/libftdxx
 */
static char *hexdump(uint8_t *buf, unsigned int size)
{
        unsigned int i;
        char *str = calloc(size * 2 + 1, 1);

        for (i = 0; i < size; i++)
                sprintf(str + 2*i, "%02x", buf[i]);
        return str;
}

static int ublast_buf_read(uint8_t *buf, unsigned size, uint32_t *bytes_read)
{
        int ret = info.drv->read(info.drv, buf, size, bytes_read);
        char *str = hexdump(buf, *bytes_read);

        DEBUG_JTAG_IO("(size=%d, buf=[%s]) -> %u", size, str,
                      *bytes_read);
        free(str);
        return ret;
}

static int ublast_buf_write(uint8_t *buf, int size, uint32_t *bytes_written)
{
        int ret = info.drv->write(info.drv, buf, size, bytes_written);
        char *str = hexdump(buf, *bytes_written);

        DEBUG_JTAG_IO("(size=%d, buf=[%s]) -> %u", size, str,
                      *bytes_written);
        free(str);
        return ret;
}

static int nb_buf_remaining(void)
{
        return BUF_LEN - info.bufidx;
}

static void ublast_flush_buffer(void)
{
        unsigned int retlen;
        int nb = info.bufidx, ret = ERROR_OK;

        while (ret == ERROR_OK && nb > 0) {
                ret = ublast_buf_write(info.buf, nb, &retlen);
                nb -= retlen;
        }
        info.bufidx = 0;
}

/*
 * Actually, the USB-Blaster offers a byte-shift mode to transmit up to 504 data
 * bits (bidirectional) in a single USB packet. A header byte has to be sent as
 * the first byte in a packet with the following meaning:
 *
 *   Bit 7 (0x80): Must be set to indicate byte-shift mode.
 *   Bit 6 (0x40): If set, the USB-Blaster will also read data, not just write.
 *   Bit 5..0:     Define the number N of following bytes
 *
 * All N following bytes will then be clocked out serially on TDI. If Bit 6 was
 * set, it will afterwards return N bytes with TDO data read while clocking out
 * the TDI data. LSB of the first byte after the header byte will appear first
 * on TDI.
 */

/* Simple bit banging mode:
 *
 *   Bit 7 (0x80): Must be zero (see byte-shift mode above)
 *   Bit 6 (0x40): If set, you will receive a byte indicating the state of TDO
 *                 in return.
 *   Bit 5 (0x20): Output Enable/LED.
 *   Bit 4 (0x10): TDI Output.
 *   Bit 3 (0x08): nCS Output (not used in JTAG mode).
 *   Bit 2 (0x04): nCE Output (not used in JTAG mode).
 *   Bit 1 (0x02): TMS Output.
 *   Bit 0 (0x01): TCK Output.
 *
 * For transmitting a single data bit, you need to write two bytes (one for
 * setting up TDI/TMS/TCK=0, and one to trigger TCK high with same TDI/TMS
 * held). Up to 64 bytes can be combined in a single USB packet.
 * It isn't possible to read a data without transmitting data.
 */

#define TCK             (1 << 0)
#define TMS             (1 << 1)
#define NCE             (1 << 2)
#define NCS             (1 << 3)
#define TDI             (1 << 4)
#define LED             (1 << 5)
#define READ            (1 << 6)
#define SHMODE          (1 << 7)
#define READ_TDO        (1 << 0)

/**
 * ublast_reset - reset the JTAG device is possible
 * @trst: 1 if TRST is to be asserted
 * @srst: 1 if SRST is to be asserted
 *
 * This is not implemented yet. If pin6 or pin8 controlls the TRST/SRST, code
 * should be added so that this function makes use of it.
 */
static void ublast_reset(int trst, int srst)
{
        DEBUG_JTAG_IO("TODO: ublast_reset(%d,%d) isn't implemented!",
                  trst, srst);
}

/**
 * ublast_queue_byte - queue one 'bitbang mode' byte for USB Blaster
 * @abyte: the byte to queue
 *
 * Queues one byte in 'bitbang mode' to the USB Blaster. The byte is not
 * actually sent, but stored in a buffer. The write is performed once
 * the buffer is filled, or if an explicit ublast_flush_buffer() is called.
 */
static void ublast_queue_byte(uint8_t abyte)
{
        if (nb_buf_remaining() < 1)
                ublast_flush_buffer();
        info.buf[info.bufidx++] = abyte;
        if (nb_buf_remaining() == 0)
                ublast_flush_buffer();
        DEBUG_JTAG_IO("(byte=0x%02x)", abyte);
}

/**
 * ublast_build_out - build bitbang mode output byte
 * @type: says if reading back TDO is required
 *
 * Returns the compute bitbang mode byte
 */
static uint8_t ublast_build_out(enum scan_type type)
{
        uint8_t abyte = 0;

        abyte |= info.tms ? TMS : 0;
        abyte |= info.pin6 ? NCE : 0;
        abyte |= info.pin8 ? NCS : 0;
        abyte |= info.tdi ? TDI : 0;
        abyte |= LED;
        if (type == SCAN_IN || type == SCAN_IO)
                abyte |= READ;
        return abyte;
}

/**
 * ublast_clock_tms - clock a TMS transition
 * @tms: the TMS to be sent
 *
 * Triggers a TMS transition (ie. one JTAG TAP state move).
 */
static void ublast_clock_tms(int tms)
{
        uint8_t out;

        DEBUG_JTAG_IO("(tms=%d)", !!tms);
        info.tms = !!tms;
        info.tdi = 0;
        out = ublast_build_out(SCAN_OUT);
        ublast_queue_byte(out);
        ublast_queue_byte(out | TCK);
}

/**
 * ublast_idle_clock - put back TCK to low level
 *
 * See ublast_queue_tdi() comment for the usage of this function.
 */
static void ublast_idle_clock(void)
{
        uint8_t out = ublast_build_out(SCAN_OUT);

        DEBUG_JTAG_IO(".");
        ublast_queue_byte(out);
}

/**
 * ublast_clock_tdi - Output a TDI with bitbang mode
 * @tdi: the TDI bit to be shifted out
 * @type: scan type (ie. does a readback of TDO is required)
 *
 * Output a TDI bit and assert clock to push it into the JTAG device :
 *  - writing out TCK=0, TMS=<old_state>=0, TDI=<tdi>
 * - writing out TCK=1, TMS=<new_state>, TDI=<tdi> which triggers the JTAG
 *    device aquiring the data.
 *
 * If a TDO is to be read back, the required read is requested (bitbang mode),
 * and the USB Blaster will send back a byte with bit0 reprensenting the TDO.
 */
static void ublast_clock_tdi(int tdi, enum scan_type type)
{
        uint8_t out;

        DEBUG_JTAG_IO("(tdi=%d)",  !!tdi);
        info.tdi = !!tdi;

        out = ublast_build_out(SCAN_OUT);
        ublast_queue_byte(out);

        out = ublast_build_out(type);
        ublast_queue_byte(out | TCK);
}

/**
 * ublast_clock_tdi_flip_tms - Output a TDI with bitbang mode, change JTAG state
 * @tdi: the TDI bit to be shifted out
 * @type: scan type (ie. does a readback of TDO is required)
 *
 * This function is the same as ublast_clock_tdi(), but it changes also the TMS
 * while outputing the TDI. This should be the last TDI output of a TDI
 * sequence, which will change state from :
 *   - IRSHIFT -> IREXIT1
 *   - or DRSHIFT -> DREXIT1
 */
static void ublast_clock_tdi_flip_tms(int tdi, enum scan_type type)
{
        uint8_t out;

        DEBUG_JTAG_IO("(tdi=%d)", !!tdi);
        info.tdi = !!tdi;
        info.tms = !info.tms;

        out = ublast_build_out(SCAN_OUT);
        ublast_queue_byte(out);

        out = ublast_build_out(type);
        ublast_queue_byte(out | TCK);

        out = ublast_build_out(SCAN_OUT);
        ublast_queue_byte(out);
}

/**
 * ublast_queue_bytes - queue bytes for the USB Blaster
 * @bytes: byte array
 * @nb_bytes: number of bytes
 *
 * Queues bytes to be sent to the USB Blaster. The bytes are not
 * actually sent, but stored in a buffer. The write is performed once
 * the buffer is filled, or if an explicit ublast_flush_buffer() is called.
 */
static void ublast_queue_bytes(uint8_t *bytes, int nb_bytes)
{
        if (info.bufidx + nb_bytes > BUF_LEN) {
                LOG_ERROR("buggy code, should never queue more that %d bytes",
                          info.bufidx + nb_bytes);
                exit(-1);
        }
        DEBUG_JTAG_IO("(nb_bytes=%d, bytes=[0x%02x, ...])", nb_bytes,
                      bytes ? bytes[0] : 0);
        if (bytes)
                memcpy(&info.buf[info.bufidx], bytes, nb_bytes);
        else
                memset(&info.buf[info.bufidx], 0, nb_bytes);
        info.bufidx += nb_bytes;
        if (nb_buf_remaining() == 0)
                ublast_flush_buffer();
}

/**
 * ublast_tms_seq - write a TMS sequence transition to JTAG
 * @bits: TMS bits to be written (bit0, bit1 .. bitN)
 * @nb_bits: number of TMS bits (between 1 and 8)
 *
 * Write a serie of TMS transitions, where each transition consists in :
 *  - writing out TCK=0, TMS=<new_state>, TDI=<???>
 *  - writing out TCK=1, TMS=<new_state>, TDI=<???> which triggers the transition
 * The function ensures that at the end of the sequence, the clock (TCK) is put
 * low.
 */
static void ublast_tms_seq(const uint8_t *bits, int nb_bits)
{
        int i;

        DEBUG_JTAG_IO("(bits=%02x..., nb_bits=%d)", bits[0], nb_bits);
        for (i = 0; i < nb_bits; i++)
                ublast_clock_tms((bits[i / 8] >> (i % 8)) & 0x01);
        ublast_idle_clock();
}

/**
 * ublast_tms - write a tms command
 * @cmd: tms command
 */
static void ublast_tms(struct tms_command *cmd)
{
        DEBUG_JTAG_IO("(num_bits=%d)", cmd->num_bits);
        ublast_tms_seq(cmd->bits, cmd->num_bits);
}

/**
 * ublast_path_move - write a TMS sequence transition to JTAG
 * @cmd: path transition
 *
 * Write a serie of TMS transitions, where each transition consists in :
 *  - writing out TCK=0, TMS=<new_state>, TDI=<???>
 *  - writing out TCK=1, TMS=<new_state>, TDI=<???> which triggers the transition
 * The function ensures that at the end of the sequence, the clock (TCK) is put
 * low.
 */
static void ublast_path_move(struct pathmove_command *cmd)
{
        int i;

        DEBUG_JTAG_IO("(num_states=%d, last_state=%d)",
                  cmd->num_states, cmd->path[cmd->num_states - 1]);
        for (i = 0; i < cmd->num_states; i++) {
                if (tap_state_transition(tap_get_state(), false) == cmd->path[i])
                        ublast_clock_tms(0);
                if (tap_state_transition(tap_get_state(), true) == cmd->path[i])
                        ublast_clock_tms(1);
                tap_set_state(cmd->path[i]);
        }
        ublast_idle_clock();
}

/**
 * ublast_state_move - move JTAG state to the target state
 * @state: the target state
 *
 * Input the correct TMS sequence to the JTAG TAP so that we end up in the
 * target state. This assumes the current state (tap_get_state()) is correct.
 */
static void ublast_state_move(tap_state_t state)
{
        uint8_t tms_scan;
        int tms_len;

        DEBUG_JTAG_IO("(from %s to %s)", tap_state_name(tap_get_state()),
                  tap_state_name(state));
        if (tap_get_state() == state)
                return;
        tms_scan = tap_get_tms_path(tap_get_state(), state);
        tms_len = tap_get_tms_path_len(tap_get_state(), state);
        ublast_tms_seq(&tms_scan, tms_len);
        tap_set_state(state);
}

/**
 * ublast_read_byteshifted_tdos - read TDO of byteshift writes
 * @buf: the buffer to store the bits
 * @nb_bits: the number of bits
 *
 * Reads back from USB Blaster TDO bits, triggered by a 'byteshift write', ie. eight
 * bits per received byte from USB interface, and store them in buffer.
 *
 * As the USB blaster stores the TDO bits in LSB (ie. first bit in (byte0,
 * bit0), second bit in (byte0, bit1), ...), which is what we want to return,
 * simply read bytes from USB interface and store them.
 *
 * Returns ERROR_OK if OK, ERROR_xxx if a read error occured
 */
static int ublast_read_byteshifted_tdos(uint8_t *buf, int nb_bytes)
{
        unsigned int retlen;
        int ret = ERROR_OK;

        DEBUG_JTAG_IO("%s(buf=%p, num_bits=%d)", __func__, buf, nb_bytes * 8);
        ublast_flush_buffer();
        while (ret == ERROR_OK && nb_bytes > 0) {
                ret = ublast_buf_read(buf, nb_bytes, &retlen);
                nb_bytes -= retlen;
        }
        return ret;
}

/**
 * ublast_read_bitbang_tdos - read TDO of bitbang writes
 * @buf: the buffer to store the bits
 * @nb_bits: the number of bits
 *
 * Reads back from USB Blaster TDO bits, triggered by a 'bitbang write', ie. one
 * bit per received byte from USB interface, and store them in buffer, where :
 *  - first bit is stored in byte0, bit0 (LSB)
 *  - second bit is stored in byte0, bit 1
 *  ...
 *  - eight bit is sotred in byte0, bit 7
 *  - ninth bit is sotred in byte1, bit 0
 *  - etc ...
 *
 * Returns ERROR_OK if OK, ERROR_xxx if a read error occured
 */
static int ublast_read_bitbang_tdos(uint8_t *buf, int nb_bits)
{
        int nb1 = nb_bits;
        int i, ret = ERROR_OK;
        unsigned int retlen;
        uint8_t tmp[8];

        DEBUG_JTAG_IO("%s(buf=%p, num_bits=%d)", __func__, buf, nb_bits);

        /*
         * Ensure all previous bitbang writes were issued to the dongle, so that
         * it returns back the read values.
         */
        ublast_flush_buffer();

        ret = ublast_buf_read(tmp, nb1, &retlen);
        for (i = 0; ret == ERROR_OK && i < nb1; i++)
                if (tmp[i] & READ_TDO)
                        *buf |= (1 << i);
                else
                        *buf &= ~(1 << i);
        return ret;
}

/**
 * ublast_queue_tdi - short description
 * @bits: bits to be queued on TDI (or NULL if 0 are to be queued)
 * @nb_bits: number of bits
 * @scan: scan type (ie. if TDO read back is required or not)
 *
 * Outputs a serie of TDI bits on TDI.
 * As a side effect, the last TDI bit is sent along a TMS=1, and triggers a JTAG
 * TAP state shift if input bits were non NULL.
 *
 * In order to not saturate the USB Blaster queues, this method reads back TDO
 * if the scan type requests it, and stores them back in bits.
 *
 * As a side note, the state of TCK when entering this function *must* be
 * low. This is because byteshift mode outputs TDI on rising TCK and reads TDO
 * on falling TCK if and only if TCK is low before queuing byteshift mode bytes.
 * If TCK was high, the USB blaster will queue TDI on falling edge, and read TDO
 * on rising edge !!!
 */
static void ublast_queue_tdi(uint8_t *bits, int nb_bits, enum scan_type scan)
{
        int nb8 = nb_bits / 8;
        int nb1 = nb_bits % 8;
        int nbfree_in_packet, i, trans = 0, read_tdos;
        uint8_t *tdos = calloc(1, nb_bits / 8 + 1);
        static uint8_t byte0[BUF_LEN];

        /*
         * As the last TDI bit should always be output in bitbang mode in order
         * to activate the TMS=1 transition to EXIT_?R state. Therefore a
         * situation where nb_bits is a multiple of 8 is handled as follows:
         * - the number of TDI shifted out in "byteshift mode" is 8 less than
         *   nb_bits
         * - nb1 = 8
         * This ensures that nb1 is never 0, and allows the TMS transition.
         */
        if (nb8 > 0 && nb1 == 0) {
                nb8--;
                nb1 = 8;
        }

        read_tdos = (scan == SCAN_IN || scan == SCAN_IO);
        for (i = 0; i < nb8; i += trans) {
                /*
                 * Calculate number of bytes to fill USB packet of size MAX_PACKET_SIZE
                 */
                nbfree_in_packet = (MAX_PACKET_SIZE - (info.bufidx%MAX_PACKET_SIZE));
                trans = MIN(nbfree_in_packet - 1, nb8 - i);

                /*
                 * Queue a byte-shift mode transmission, with as many bytes as
                 * is possible with regard to :
                 *  - current filling level of write buffer
                 *  - remaining bytes to write in byte-shift mode
                 */
                if (read_tdos)
                        ublast_queue_byte(SHMODE | READ | trans);
                else
                        ublast_queue_byte(SHMODE | trans);
                if (bits)
                        ublast_queue_bytes(&bits[i], trans);
                else
                        ublast_queue_bytes(byte0, trans);
                if (read_tdos)
                        ublast_read_byteshifted_tdos(&tdos[i], trans);
        }

        /*
         * Queue the remaining TDI bits in bitbang mode.
         */
        for (i = 0; i < nb1; i++) {
                int tdi = bits ? bits[nb8 + i / 8] & (1 << i) : 0;
                if (bits && i == nb1 - 1)
                        ublast_clock_tdi_flip_tms(tdi, scan);
                else
                        ublast_clock_tdi(tdi, scan);
        }
        if (nb1 && read_tdos)
                ublast_read_bitbang_tdos(&tdos[nb8], nb1);

        if (bits)
                memcpy(bits, tdos, DIV_ROUND_UP(nb_bits, 8));
        free(tdos);

        /*
         * Ensure clock is in lower state
         */
        ublast_idle_clock();
}

static void ublast_runtest(int cycles, tap_state_t state)
{
        DEBUG_JTAG_IO("%s(cycles=%i, end_state=%d)", __func__, cycles, state);

        ublast_state_move(TAP_IDLE);
        ublast_queue_tdi(NULL, cycles, SCAN_OUT);
        ublast_state_move(state);
}

static void ublast_stableclocks(int cycles)
{
        DEBUG_JTAG_IO("%s(cycles=%i)", __func__, cycles);
        ublast_queue_tdi(NULL, cycles, SCAN_OUT);
}

/**
 * ublast_scan - launches a DR-scan or IR-scan
 * @cmd: the command to launch
 *
 * Launch a JTAG IR-scan or DR-scan
 *
 * Returns ERROR_OK if OK, ERROR_xxx if a read/write error occured.
 */
static int ublast_scan(struct scan_command *cmd)
{
        int scan_bits;
        uint8_t *buf = NULL;
        enum scan_type type;
        int ret = ERROR_OK;
        static const char * const type2str[] = { "", "SCAN_IN", "SCAN_OUT", "SCAN_IO" };
        char *log_buf = NULL;

        type = jtag_scan_type(cmd);
        scan_bits = jtag_build_buffer(cmd, &buf);

        if (cmd->ir_scan)
                ublast_state_move(TAP_IRSHIFT);
        else
                ublast_state_move(TAP_DRSHIFT);

        log_buf = hexdump(buf, DIV_ROUND_UP(scan_bits, 8));
        DEBUG_JTAG_IO("%s(scan=%s, type=%s, bits=%d, buf=[%s], end_state=%d)", __func__,
                  cmd->ir_scan ? "IRSCAN" : "DRSCAN",
                  type2str[type],
                  scan_bits, log_buf, cmd->end_state);
        free(log_buf);

        ublast_queue_tdi(buf, scan_bits, type);

        /*
         * As our JTAG is in an unstable state (IREXIT1 or DREXIT1), move it
         * forward to a stable IRPAUSE or DRPAUSE.
         */
        ublast_clock_tms(0);
        if (cmd->ir_scan)
                tap_set_state(TAP_IRPAUSE);
        else
                tap_set_state(TAP_DRPAUSE);

        ret = jtag_read_buffer(buf, cmd);
        if (buf)
                free(buf);
        ublast_state_move(cmd->end_state);
        return ret;
}

static void ublast_msleep(int ms)
{
        DEBUG_JTAG_IO("%s(ms=%d)",  __func__, ms);
        jtag_sleep(ms);
}

static int ublast_execute_queue(void)
{
        struct jtag_command *cmd;
        int ret = ERROR_OK;

        for (cmd = jtag_command_queue; ret == ERROR_OK && cmd != NULL;
             cmd = cmd->next) {
                switch (cmd->type) {
                case JTAG_RESET:
                        ublast_reset(cmd->cmd.reset->trst, cmd->cmd.reset->srst);
                        break;
                case JTAG_RUNTEST:
                        ublast_runtest(cmd->cmd.runtest->num_cycles,
                                       cmd->cmd.runtest->end_state);
                        break;
                case JTAG_STABLECLOCKS:
                        ublast_stableclocks(cmd->cmd.stableclocks->num_cycles);
                        break;
                case JTAG_TLR_RESET:
                        ublast_state_move(cmd->cmd.statemove->end_state);
                        break;
                case JTAG_PATHMOVE:
                        ublast_path_move(cmd->cmd.pathmove);
                        break;
                case JTAG_TMS:
                        ublast_tms(cmd->cmd.tms);
                        break;
                case JTAG_SLEEP:
                        ublast_msleep(cmd->cmd.sleep->us);
                        break;
                case JTAG_SCAN:
                        ret = ublast_scan(cmd->cmd.scan);
                        break;
                }
        }

        ublast_flush_buffer();
        return ret;
}

/**
 * ublast_init - Initialize the Altera device
 *
 * Initialize the device :
 *  - open the USB device
 *  - empty the write FIFO (128 bytes)
 *  - empty the read FIFO (384 bytes)
 *
 * Returns ERROR_OK if USB device found, error if not.
 */
static int ublast_init(void)
{
        static uint8_t tms_reset = 0xff;
        int ret, i;

        if (info.lowlevel_name) {
                for (i = 0; lowlevel_drivers_map[i].name; i++)
                        if (!strcmp(lowlevel_drivers_map[i].name, info.lowlevel_name))
                                break;
                if (lowlevel_drivers_map[i].name)
                        info.drv = lowlevel_drivers_map[i].drv_register();
                if (!info.drv) {
                        LOG_ERROR("no lowlevel driver found for %s or lowlevel driver opening error",
                                  info.lowlevel_name);
                        return ERROR_JTAG_DEVICE_ERROR;
                }
        } else {
                LOG_INFO("No lowlevel driver configured, will try them all");
                for (i = 0; !info.drv && lowlevel_drivers_map[i].name; i++)
                        info.drv = lowlevel_drivers_map[i].drv_register();
                if (!info.drv) {
                        LOG_ERROR("no lowlevel driver found");
                        return ERROR_JTAG_DEVICE_ERROR;
                }
        }

        /*
         * Register the lowlevel driver
         */
        info.drv->ublast_vid = info.ublast_vid;
        info.drv->ublast_pid = info.ublast_pid;
        info.drv->ublast_device_desc = info.ublast_device_desc;

        ret = info.drv->open(info.drv);
        if (ret == ERROR_OK) {
                /*
                 * Flush USB-Blaster queue fifos
                 */
                uint32_t retlen;
                ublast_buf_write(info.buf, BUF_LEN, &retlen);
                /*
                 * Put JTAG in RESET state (five 1 on TMS)
                 */
                ublast_tms_seq(&tms_reset, 5);
                tap_set_state(TAP_RESET);
        }
        return ret;
}

/**
 * ublast_quit - Release the Altera device
 *
 * Releases the device :
 *   - put the device pins in 'high impedance' mode
 *   - close the USB device
 *
 * Returns always ERROR_OK
 */
static int ublast_quit(void)
{
        uint8_t byte0 = 0;
        unsigned int retlen;

        ublast_buf_write(&byte0, 1, &retlen);
        return info.drv->close(info.drv);
}

COMMAND_HANDLER(ublast_handle_device_desc_command)
{
        if (CMD_ARGC == 1)
                info.ublast_device_desc = strdup(CMD_ARGV[0]);
        else
                LOG_ERROR("require exactly one argument to "
                                  "ublast_device_desc <description>");

        return ERROR_OK;
}

COMMAND_HANDLER(ublast_handle_vid_pid_command)
{
        if (CMD_ARGC > 2) {
                LOG_WARNING("ignoring extra IDs in ublast_vid_pid "
                                        "(maximum is 1 pair)");
                CMD_ARGC = 2;
        }
        if (CMD_ARGC == 2) {
                COMMAND_PARSE_NUMBER(u16, CMD_ARGV[0], info.ublast_vid);
                COMMAND_PARSE_NUMBER(u16, CMD_ARGV[1], info.ublast_pid);
        } else {
                LOG_WARNING("incomplete ublast_vid_pid configuration");
        }

        return ERROR_OK;
}

COMMAND_HANDLER(ublast_handle_pin_command)
{
        uint8_t out_value;

        if (CMD_ARGC == 2) {
                const char * const pin_name = CMD_ARGV[0];
                unsigned int state;

                COMMAND_PARSE_NUMBER(uint, CMD_ARGV[1], state);
                if ((state != 0) && (state != 1)) {
                        LOG_ERROR("%s: pin state must be 0 or 1", CMD_NAME);
                        return ERROR_COMMAND_SYNTAX_ERROR;
                }

                if (!strcmp(pin_name, "pin6")) {
                        info.pin6 = state;
                } else if (!strcmp(pin_name, "pin8")) {
                        info.pin8 = state;
                } else {
                        LOG_ERROR("%s: pin name must be \"pin6\" or \"pin8\"",
                                        CMD_NAME);
                        return ERROR_COMMAND_SYNTAX_ERROR;
                }

                if (info.drv) {
                        out_value = ublast_build_out(SCAN_OUT);
                        ublast_queue_byte(out_value);
                        ublast_flush_buffer();
                }
                return ERROR_OK;
        } else {
                LOG_ERROR("%s takes exactly two arguments", CMD_NAME);
                return ERROR_COMMAND_SYNTAX_ERROR;
        }
}

COMMAND_HANDLER(ublast_handle_lowlevel_drv_command)
{
        if (CMD_ARGC == 1)
                info.lowlevel_name = strdup(CMD_ARGV[0]);
        else
                LOG_ERROR("require exactly one argument to "
                                  "usb_blaster_lowlevel_driver (ftdi|ftd2xx)");
        return ERROR_OK;
}

static const struct command_registration ublast_command_handlers[] = {
        {
                .name = "usb_blaster_device_desc",
                .handler = ublast_handle_device_desc_command,
                .mode = COMMAND_CONFIG,
                .help = "set the USB device description of the USB-Blaster",
                .usage = "description-string",
        },
        {
                .name = "usb_blaster_vid_pid",
                .handler = ublast_handle_vid_pid_command,
                .mode = COMMAND_CONFIG,
                .help = "the vendor ID and product ID of the USB-Blaster",
                .usage = "vid pid",
        },
        {
                .name = "usb_blaster_lowlevel_driver",
                .handler = ublast_handle_lowlevel_drv_command,
                .mode = COMMAND_CONFIG,
                .help = "set the lowlevel access for the USB Blaster (ftdi, ftd2xx)",
                .usage = "(ftdi|ftd2xx)",
        },
        {
                .name = "usb_blaster",
                .handler = ublast_handle_pin_command,
                .mode = COMMAND_ANY,
                .help = "set pin state for the unused GPIO pins",
                .usage = "(pin6|pin8) (0|1)",
        },
        COMMAND_REGISTRATION_DONE
};

struct jtag_interface usb_blaster_interface = {
        .name = "usb_blaster",
        .commands = ublast_command_handlers,
        .supported = DEBUG_CAP_TMS_SEQ,

        .execute_queue = ublast_execute_queue,
        .init = ublast_init,
        .quit = ublast_quit,
};