arm-jtag-ew.c

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// SPDX-License-Identifier: GPL-2.0-or-later
 
/***************************************************************************
 *   Copyright (C) 2009 by Dimitar Dimitrov <dinuxbg@gmail.com>            *
 *   based on Dominic Rath's and Benedikt Sauter's usbprog.c               *
 ***************************************************************************/
 
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
 
#include <jtag/interface.h>
#include <jtag/commands.h>
#include "helper/system.h"
#include "libusb_helper.h"
 
#define USB_VID                     0x15ba
#define USB_PID                     0x001e
 
#define ARMJTAGEW_EPT_BULK_OUT      0x01u
#define ARMJTAGEW_EPT_BULK_IN       0x82u
 
#define ARMJTAGEW_USB_TIMEOUT       2000
 
#define ARMJTAGEW_IN_BUFFER_SIZE    (4*1024)
#define ARMJTAGEW_OUT_BUFFER_SIZE   (4*1024)
 
/* USB command request codes. */
#define CMD_GET_VERSION             0x00
#define CMD_SELECT_DPIMPL           0x10
#define CMD_SET_TCK_FREQUENCY       0x11
#define CMD_GET_TCK_FREQUENCY       0x12
#define CMD_MEASURE_MAX_TCK_FREQ    0x15
#define CMD_MEASURE_RTCK_RESPONSE   0x16
#define CMD_TAP_SHIFT               0x17
#define CMD_SET_TAPHW_STATE         0x20
#define CMD_GET_TAPHW_STATE         0x21
#define CMD_TGPWR_SETUP             0x22
 
/* Global USB buffers */
static uint8_t usb_in_buffer[ARMJTAGEW_IN_BUFFER_SIZE];
static uint8_t usb_out_buffer[ARMJTAGEW_OUT_BUFFER_SIZE];
 
/* Queue command functions */
static void armjtagew_end_state(tap_state_t state);
static void armjtagew_state_move(void);
static void armjtagew_path_move(unsigned int num_states, tap_state_t *path);
static void armjtagew_runtest(unsigned int num_cycles);
static void armjtagew_scan(bool ir_scan,
        enum scan_type type,
        uint8_t *buffer,
        int scan_size,
        struct scan_command *command);
static void armjtagew_reset(int trst, int srst);
/* static void armjtagew_simple_command(uint8_t command); */
static int armjtagew_get_status(void);
 
/* tap buffer functions */
static void armjtagew_tap_init(void);
static int armjtagew_tap_execute(void);
static void armjtagew_tap_ensure_space(int scans, int bits);
static void armjtagew_tap_append_step(int tms, int tdi);
static void armjtagew_tap_append_scan(int length, uint8_t *buffer, struct scan_command *command);
 
/* ARM-JTAG-EW lowlevel functions */
struct armjtagew {
    struct libusb_device_handle *usb_handle;
};
 
static struct armjtagew *armjtagew_usb_open(void);
static void armjtagew_usb_close(struct armjtagew *armjtagew);
static int armjtagew_usb_message(struct armjtagew *armjtagew, int out_length, int in_length);
static int armjtagew_usb_write(struct armjtagew *armjtagew, int out_length);
static int armjtagew_usb_read(struct armjtagew *armjtagew, int exp_in_length);
 
/* helper functions */
static int armjtagew_get_version_info(void);
 
#ifdef _DEBUG_USB_COMMS_
static void armjtagew_debug_buffer(uint8_t *buffer, int length);
#endif
 
static struct armjtagew *armjtagew_handle;
 
/**************************************************************************
 * External interface implementation */
 
static int armjtagew_execute_queue(struct jtag_command *cmd_queue)
{
    struct jtag_command *cmd = cmd_queue;
    int scan_size;
    enum scan_type type;
    uint8_t *buffer;
 
    while (cmd) {
        switch (cmd->type) {
            case JTAG_RUNTEST:
                LOG_DEBUG_IO("runtest %u cycles, end in %i",
                        cmd->cmd.runtest->num_cycles,
                        cmd->cmd.runtest->end_state);
 
                armjtagew_end_state(cmd->cmd.runtest->end_state);
                armjtagew_runtest(cmd->cmd.runtest->num_cycles);
                break;
 
            case JTAG_TLR_RESET:
                LOG_DEBUG_IO("statemove end in %i", cmd->cmd.statemove->end_state);
 
                armjtagew_end_state(cmd->cmd.statemove->end_state);
                armjtagew_state_move();
                break;
 
            case JTAG_PATHMOVE:
                LOG_DEBUG_IO("pathmove: %u states, end in %i",
                        cmd->cmd.pathmove->num_states,
                        cmd->cmd.pathmove->path[cmd->cmd.pathmove->num_states - 1]);
 
                armjtagew_path_move(cmd->cmd.pathmove->num_states,
                        cmd->cmd.pathmove->path);
                break;
 
            case JTAG_SCAN:
                LOG_DEBUG_IO("scan end in %i", cmd->cmd.scan->end_state);
 
                armjtagew_end_state(cmd->cmd.scan->end_state);
 
                scan_size = jtag_build_buffer(cmd->cmd.scan, &buffer);
                LOG_DEBUG_IO("scan input, length = %d", scan_size);
 
#ifdef _DEBUG_USB_COMMS_
                armjtagew_debug_buffer(buffer, (scan_size + 7) / 8);
#endif
                type = jtag_scan_type(cmd->cmd.scan);
                armjtagew_scan(cmd->cmd.scan->ir_scan,
                        type, buffer,
                        scan_size, cmd->cmd.scan);
                break;
 
            case JTAG_RESET:
                LOG_DEBUG_IO("reset trst: %i srst %i",
                        cmd->cmd.reset->trst,
                        cmd->cmd.reset->srst);
 
                armjtagew_tap_execute();
 
                if (cmd->cmd.reset->trst == 1)
                    tap_set_state(TAP_RESET);
                armjtagew_reset(cmd->cmd.reset->trst, cmd->cmd.reset->srst);
                break;
 
            case JTAG_SLEEP:
                LOG_DEBUG_IO("sleep %" PRIu32, cmd->cmd.sleep->us);
                armjtagew_tap_execute();
                jtag_sleep(cmd->cmd.sleep->us);
                break;
 
            default:
                LOG_ERROR("BUG: unknown JTAG command type encountered");
                exit(-1);
        }
        cmd = cmd->next;
    }
 
    return armjtagew_tap_execute();
}
 
/* Sets speed in kHz. */
static int armjtagew_speed(int speed)
{
    int result;
    int speed_real;
 
 
    usb_out_buffer[0] = CMD_SET_TCK_FREQUENCY;
    buf_set_u32(usb_out_buffer + 1, 0, 32, speed*1000);
 
    result = armjtagew_usb_message(armjtagew_handle, 5, 4);
 
    if (result < 0) {
        LOG_ERROR("ARM-JTAG-EW setting speed failed (%d)", result);
        return ERROR_JTAG_DEVICE_ERROR;
    }
 
    usb_out_buffer[0] = CMD_GET_TCK_FREQUENCY;
    result = armjtagew_usb_message(armjtagew_handle, 1, 4);
    speed_real = (int)buf_get_u32(usb_in_buffer, 0, 32) / 1000;
    if (result < 0) {
        LOG_ERROR("ARM-JTAG-EW getting speed failed (%d)", result);
        return ERROR_JTAG_DEVICE_ERROR;
    } else
        LOG_INFO("Requested speed %dkHz, emulator reported %dkHz.", speed, speed_real);
 
    return ERROR_OK;
}
 
static int armjtagew_khz(int khz, int *jtag_speed)
{
    *jtag_speed = khz;
 
    return ERROR_OK;
}
 
static int armjtagew_speed_div(int speed, int *khz)
{
    *khz = speed;
 
    return ERROR_OK;
}
 
static int armjtagew_init(void)
{
    int check_cnt;
 
    armjtagew_handle = armjtagew_usb_open();
 
    if (!armjtagew_handle) {
        LOG_ERROR(
            "Cannot find ARM-JTAG-EW Interface! Please check connection and permissions.");
        return ERROR_JTAG_INIT_FAILED;
    }
 
    check_cnt = 0;
    while (check_cnt < 3) {
        if (armjtagew_get_version_info() == ERROR_OK) {
            /* attempt to get status */
            armjtagew_get_status();
            break;
        }
 
        check_cnt++;
    }
 
    if (check_cnt == 3)
        LOG_INFO("ARM-JTAG-EW initial read failed, don't worry");
 
    /* Initial JTAG speed (for reset and initialization): 32 kHz */
    armjtagew_speed(32);
 
    LOG_INFO("ARM-JTAG-EW JTAG Interface ready");
 
    armjtagew_reset(0, 0);
    armjtagew_tap_init();
 
    return ERROR_OK;
}
 
static int armjtagew_quit(void)
{
    armjtagew_usb_close(armjtagew_handle);
    return ERROR_OK;
}
 
/**************************************************************************
 * Queue command implementations */
 
static void armjtagew_end_state(tap_state_t state)
{
    if (tap_is_state_stable(state))
        tap_set_end_state(state);
    else {
        LOG_ERROR("BUG: %i is not a valid end state", state);
        exit(-1);
    }
}
 
/* Goes to the end state. */
static void armjtagew_state_move(void)
{
    int i;
    int tms = 0;
    uint8_t tms_scan = tap_get_tms_path(tap_get_state(), tap_get_end_state());
    int tms_count = tap_get_tms_path_len(tap_get_state(), tap_get_end_state());
 
    for (i = 0; i < tms_count; i++) {
        tms = (tms_scan >> i) & 1;
        armjtagew_tap_append_step(tms, 0);
    }
 
    tap_set_state(tap_get_end_state());
}
 
static void armjtagew_path_move(unsigned int num_states, tap_state_t *path)
{
    for (unsigned int i = 0; i < num_states; i++) {
        /*
         * TODO: The ARM-JTAG-EW hardware delays TDI with 3 TCK cycles when in RTCK mode.
         * Either handle that here, or update the documentation with examples
         * how to fix that in the configuration files.
         */
        if (path[i] == tap_state_transition(tap_get_state(), false))
            armjtagew_tap_append_step(0, 0);
        else if (path[i] == tap_state_transition(tap_get_state(), true))
            armjtagew_tap_append_step(1, 0);
        else {
            LOG_ERROR("BUG: %s -> %s isn't a valid TAP transition",
                tap_state_name(tap_get_state()), tap_state_name(path[i]));
            exit(-1);
        }
 
        tap_set_state(path[i]);
    }
 
    tap_set_end_state(tap_get_state());
}
 
static void armjtagew_runtest(unsigned int num_cycles)
{
    tap_state_t saved_end_state = tap_get_end_state();
 
    /* only do a state_move when we're not already in IDLE */
    if (tap_get_state() != TAP_IDLE) {
        armjtagew_end_state(TAP_IDLE);
        armjtagew_state_move();
    }
 
    /* execute num_cycles */
    for (unsigned int i = 0; i < num_cycles; i++)
        armjtagew_tap_append_step(0, 0);
 
    /* finish in end_state */
    armjtagew_end_state(saved_end_state);
    if (tap_get_state() != tap_get_end_state())
        armjtagew_state_move();
}
 
static void armjtagew_scan(bool ir_scan,
    enum scan_type type,
    uint8_t *buffer,
    int scan_size,
    struct scan_command *command)
{
    tap_state_t saved_end_state;
 
    armjtagew_tap_ensure_space(1, scan_size + 8);
 
    saved_end_state = tap_get_end_state();
 
    /* Move to appropriate scan state */
    armjtagew_end_state(ir_scan ? TAP_IRSHIFT : TAP_DRSHIFT);
 
    /* Only move if we're not already there */
    if (tap_get_state() != tap_get_end_state())
        armjtagew_state_move();
 
    armjtagew_end_state(saved_end_state);
 
    /* Scan */
    armjtagew_tap_append_scan(scan_size, buffer, command);
 
    /* We are in Exit1, go to Pause */
    armjtagew_tap_append_step(0, 0);
 
    tap_set_state(ir_scan ? TAP_IRPAUSE : TAP_DRPAUSE);
 
    if (tap_get_state() != tap_get_end_state())
        armjtagew_state_move();
}
 
static void armjtagew_reset(int trst, int srst)
{
    const uint8_t trst_mask = (1u << 5);
    const uint8_t srst_mask = (1u << 6);
    uint8_t val = 0;
    uint8_t outp_en = 0;
    uint8_t change_mask = 0;
    int result;
 
    LOG_DEBUG("trst: %i, srst: %i", trst, srst);
 
    if (srst == 0) {
        val |= srst_mask;
        outp_en &= ~srst_mask;      /* tristate */
        change_mask |= srst_mask;
    } else if (srst == 1) {
        val &= ~srst_mask;
        outp_en |= srst_mask;
        change_mask |= srst_mask;
    }
 
    if (trst == 0) {
        val |= trst_mask;
        outp_en &= ~trst_mask;      /* tristate */
        change_mask |= trst_mask;
    } else if (trst == 1) {
        val &= ~trst_mask;
        outp_en |= trst_mask;
        change_mask |= trst_mask;
    }
 
    usb_out_buffer[0] = CMD_SET_TAPHW_STATE;
    usb_out_buffer[1] = val;
    usb_out_buffer[2] = outp_en;
    usb_out_buffer[3] = change_mask;
    result = armjtagew_usb_write(armjtagew_handle, 4);
    if (result != 4)
        LOG_ERROR("ARM-JTAG-EW TRST/SRST pin set failed failed (%d)", result);
}
 
static int armjtagew_get_status(void)
{
    int result;
 
    usb_out_buffer[0] = CMD_GET_TAPHW_STATE;
    result = armjtagew_usb_message(armjtagew_handle, 1, 12);
 
    if (result == 0) {
        unsigned int u_tg = buf_get_u32(usb_in_buffer, 0, 16);
        LOG_INFO(
            "U_tg = %d mV, U_aux = %d mV, U_tgpwr = %d mV, I_tgpwr = %d mA, D1 = %d, Target power %s %s",
            (int)(buf_get_u32(usb_in_buffer + 0, 0, 16)),
            (int)(buf_get_u32(usb_in_buffer + 2, 0, 16)),
            (int)(buf_get_u32(usb_in_buffer + 4, 0, 16)),
            (int)(buf_get_u32(usb_in_buffer + 6, 0, 16)),
            usb_in_buffer[9],
            usb_in_buffer[11] ? "OVERCURRENT" : "OK",
            usb_in_buffer[10] ? "enabled" : "disabled");
 
        if (u_tg < 1500)
            LOG_ERROR("Vref too low. Check Target Power");
    } else
        LOG_ERROR("ARM-JTAG-EW command CMD_GET_TAPHW_STATE failed (%d)", result);
 
    return ERROR_OK;
}
 
static int armjtagew_get_version_info(void)
{
    int result;
    char sn[16];
    char auxinfo[257];
 
    /* query hardware version */
    usb_out_buffer[0] = CMD_GET_VERSION;
    result = armjtagew_usb_message(armjtagew_handle, 1, 4 + 15 + 256);
 
    if (result != 0) {
        LOG_ERROR("ARM-JTAG-EW command CMD_GET_VERSION failed (%d)", result);
        return ERROR_JTAG_DEVICE_ERROR;
    }
 
    memcpy(sn, usb_in_buffer + 4, 15);
    sn[15] = '\0';
    memcpy(auxinfo, usb_in_buffer + 4+15, 256);
    auxinfo[256] = '\0';
 
    LOG_INFO(
        "ARM-JTAG-EW firmware version %d.%d, hardware revision %c, SN=%s, Additional info: %s",
        usb_in_buffer[1],
        usb_in_buffer[0],
        isgraph(usb_in_buffer[2]) ? usb_in_buffer[2] : 'X',
        sn,
        auxinfo);
 
    if (1 != usb_in_buffer[1] || 6 != usb_in_buffer[0])
        LOG_WARNING(
            "ARM-JTAG-EW firmware version %d.%d is untested with this version of OpenOCD. You might experience unexpected behavior.",
            usb_in_buffer[1],
            usb_in_buffer[0]);
    return ERROR_OK;
}
 
COMMAND_HANDLER(armjtagew_handle_armjtagew_info_command)
{
    if (armjtagew_get_version_info() == ERROR_OK) {
        /* attempt to get status */
        armjtagew_get_status();
    }
 
    return ERROR_OK;
}
 
static const struct command_registration armjtagew_command_handlers[] = {
    {
        .name = "armjtagew_info",
        .handler = &armjtagew_handle_armjtagew_info_command,
        .mode = COMMAND_EXEC,
        .help = "query armjtagew info",
        .usage = "",
    },
    COMMAND_REGISTRATION_DONE
};
 
static struct jtag_interface armjtagew_interface = {
    .execute_queue = armjtagew_execute_queue,
};
 
struct adapter_driver armjtagew_adapter_driver = {
    .name = "arm-jtag-ew",
    .transports = jtag_only,
    .commands = armjtagew_command_handlers,
 
    .init = armjtagew_init,
    .quit = armjtagew_quit,
    .speed = armjtagew_speed,
    .khz = armjtagew_khz,
    .speed_div = armjtagew_speed_div,
 
    .jtag_ops = &armjtagew_interface,
};
 
/**************************************************************************
 * ARM-JTAG-EW tap functions */
 
/* 2048 is the max value we can use here */
#define ARMJTAGEW_TAP_BUFFER_SIZE 2048
 
static int tap_length;
static uint8_t tms_buffer[ARMJTAGEW_TAP_BUFFER_SIZE];
static uint8_t tdi_buffer[ARMJTAGEW_TAP_BUFFER_SIZE];
static uint8_t tdo_buffer[ARMJTAGEW_TAP_BUFFER_SIZE];
 
struct pending_scan_result {
    int first;  /* First bit position in tdo_buffer to read */
    int length; /* Number of bits to read */
    struct scan_command *command;   /* Corresponding scan command */
    uint8_t *buffer;
};
 
#define MAX_PENDING_SCAN_RESULTS 256
 
static int pending_scan_results_length;
static struct pending_scan_result pending_scan_results_buffer[MAX_PENDING_SCAN_RESULTS];
 
static int last_tms;
 
static void armjtagew_tap_init(void)
{
    tap_length = 0;
    pending_scan_results_length = 0;
}
 
static void armjtagew_tap_ensure_space(int scans, int bits)
{
    int available_scans = MAX_PENDING_SCAN_RESULTS - pending_scan_results_length;
    int available_bits = ARMJTAGEW_TAP_BUFFER_SIZE * 8 - tap_length;
 
    if (scans > available_scans || bits > available_bits)
        armjtagew_tap_execute();
}
 
static void armjtagew_tap_append_step(int tms, int tdi)
{
    last_tms = tms;
    int index_local = tap_length / 8;
 
    if (index_local < ARMJTAGEW_TAP_BUFFER_SIZE) {
        int bit_index = tap_length % 8;
        uint8_t bit = 1 << bit_index;
 
        if (tms)
            tms_buffer[index_local] |= bit;
        else
            tms_buffer[index_local] &= ~bit;
 
        if (tdi)
            tdi_buffer[index_local] |= bit;
        else
            tdi_buffer[index_local] &= ~bit;
 
        tap_length++;
    } else
        LOG_ERROR("armjtagew_tap_append_step, overflow");
}
 
void armjtagew_tap_append_scan(int length, uint8_t *buffer, struct scan_command *command)
{
    struct pending_scan_result *pending_scan_result =
        &pending_scan_results_buffer[pending_scan_results_length];
    int i;
 
    pending_scan_result->first = tap_length;
    pending_scan_result->length = length;
    pending_scan_result->command = command;
    pending_scan_result->buffer = buffer;
 
    for (i = 0; i < length; i++)
        armjtagew_tap_append_step((i < length-1 ? 0 : 1), (buffer[i/8] >> (i%8)) & 1);
    pending_scan_results_length++;
}
 
/* Pad and send a tap sequence to the device, and receive the answer.
 * For the purpose of padding we assume that we are in idle or pause state. */
static int armjtagew_tap_execute(void)
{
    int byte_length;
    int tms_offset;
    int tdi_offset;
    int i;
    int result;
 
    if (tap_length > 0) {
        /* Pad last byte so that tap_length is divisible by 8 */
        while (tap_length % 8 != 0) {
            /* More of the last TMS value keeps us in the same state,
             * analogous to free-running JTAG interfaces. */
            armjtagew_tap_append_step(last_tms, 0);
        }
 
        byte_length = tap_length / 8;
 
        usb_out_buffer[0] = CMD_TAP_SHIFT;
        buf_set_u32(usb_out_buffer + 1, 0, 16, byte_length);
 
        tms_offset = 3;
        for (i = 0; i < byte_length; i++)
            usb_out_buffer[tms_offset + i] = flip_u32(tms_buffer[i], 8);
 
        tdi_offset = tms_offset + byte_length;
        for (i = 0; i < byte_length; i++)
            usb_out_buffer[tdi_offset + i] = flip_u32(tdi_buffer[i], 8);
 
        result = armjtagew_usb_message(armjtagew_handle,
                3 + 2 * byte_length,
                byte_length + 4);
 
        if (result == 0) {
            int stat_local;
 
            stat_local = (int)buf_get_u32(usb_in_buffer + byte_length, 0, 32);
            if (stat_local) {
                LOG_ERROR(
                    "armjtagew_tap_execute, emulator returned error code %d for a CMD_TAP_SHIFT command",
                    stat_local);
                return ERROR_JTAG_QUEUE_FAILED;
            }
 
            for (i = 0; i < byte_length; i++)
                tdo_buffer[i] = flip_u32(usb_in_buffer[i], 8);
 
            for (i = 0; i < pending_scan_results_length; i++) {
                struct pending_scan_result *pending_scan_result =
                    &pending_scan_results_buffer[i];
                uint8_t *buffer = pending_scan_result->buffer;
                int length = pending_scan_result->length;
                int first = pending_scan_result->first;
                struct scan_command *command = pending_scan_result->command;
 
                /* Copy to buffer */
                buf_set_buf(tdo_buffer, first, buffer, 0, length);
 
                LOG_DEBUG_IO("pending scan result, length = %d", length);
 
#ifdef _DEBUG_USB_COMMS_
                armjtagew_debug_buffer(buffer, byte_length);
#endif
 
                if (jtag_read_buffer(buffer, command) != ERROR_OK) {
                    armjtagew_tap_init();
                    return ERROR_JTAG_QUEUE_FAILED;
                }
 
                free(pending_scan_result->buffer);
            }
        } else {
            LOG_ERROR("armjtagew_tap_execute, wrong result %d, expected %d",
                result,
                byte_length);
            return ERROR_JTAG_QUEUE_FAILED;
        }
 
        armjtagew_tap_init();
    }
 
    return ERROR_OK;
}
 
/****************************************************************************
 * JLink USB low-level functions */
 
static struct armjtagew *armjtagew_usb_open(void)
{
    const uint16_t vids[] = { USB_VID, 0 };
    const uint16_t pids[] = { USB_PID, 0 };
    struct libusb_device_handle *dev;
 
    if (jtag_libusb_open(vids, pids, NULL, &dev, NULL) != ERROR_OK)
        return NULL;
 
    struct armjtagew *result = malloc(sizeof(struct armjtagew));
    result->usb_handle = dev;
 
#if 0
    /* libusb_set_configuration required under win32 */
    struct libusb_config_descriptor *config;
    struct libusb_device *usb_dev = libusb_get_device(dev);
    libusb_get_config_descriptor(usb_dev, 0, &config);
    libusb_set_configuration(dev, config->bConfigurationValue);
#endif
    libusb_claim_interface(dev, 0);
#if 0
    /*
     * This makes problems under Mac OS X. And is not needed
     * under Windows. Hopefully this will not break a linux build
     */
    libusb_set_interface_alt_setting(dev, 0, 0);
#endif
    return result;
}
 
static void armjtagew_usb_close(struct armjtagew *armjtagew)
{
    libusb_close(armjtagew->usb_handle);
    free(armjtagew);
}
 
/* Send a message and receive the reply. */
static int armjtagew_usb_message(struct armjtagew *armjtagew, int out_length, int in_length)
{
    int result;
 
    result = armjtagew_usb_write(armjtagew, out_length);
    if (result == out_length) {
        result = armjtagew_usb_read(armjtagew, in_length);
        if (result != in_length) {
            LOG_ERROR("jtag_libusb_bulk_read failed (requested=%d, result=%d)",
                in_length,
                result);
            return -1;
        }
    } else {
        LOG_ERROR("jtag_libusb_bulk_write failed (requested=%d, result=%d)", out_length, result);
        return -1;
    }
    return 0;
}
 
/* Write data from out_buffer to USB. */
static int armjtagew_usb_write(struct armjtagew *armjtagew, int out_length)
{
    int result;
    int transferred;
 
    if (out_length > ARMJTAGEW_OUT_BUFFER_SIZE) {
        LOG_ERROR("armjtagew_write illegal out_length=%d (max=%d)",
            out_length,
            ARMJTAGEW_OUT_BUFFER_SIZE);
        return -1;
    }
 
    result = jtag_libusb_bulk_write(armjtagew->usb_handle, ARMJTAGEW_EPT_BULK_OUT,
            (char *)usb_out_buffer, out_length, ARMJTAGEW_USB_TIMEOUT, &transferred);
 
    LOG_DEBUG_IO("armjtagew_usb_write, out_length = %d, result = %d", out_length, result);
 
#ifdef _DEBUG_USB_COMMS_
    armjtagew_debug_buffer(usb_out_buffer, out_length);
#endif
    if (result != ERROR_OK)
        return -1;
    return transferred;
}
 
/* Read data from USB into in_buffer. */
static int armjtagew_usb_read(struct armjtagew *armjtagew, int exp_in_length)
{
    int transferred;
    int result = jtag_libusb_bulk_read(armjtagew->usb_handle, ARMJTAGEW_EPT_BULK_IN,
            (char *)usb_in_buffer, exp_in_length, ARMJTAGEW_USB_TIMEOUT, &transferred);
 
    LOG_DEBUG_IO("armjtagew_usb_read, result = %d", result);
 
#ifdef _DEBUG_USB_COMMS_
    armjtagew_debug_buffer(usb_in_buffer, result);
#endif
    if (result != ERROR_OK)
        return -1;
    return transferred;
}
 
#ifdef _DEBUG_USB_COMMS_
#define BYTES_PER_LINE  16
 
static void armjtagew_debug_buffer(uint8_t *buffer, int length)
{
    char line[8 + 3 * BYTES_PER_LINE + 1];
 
    for (int i = 0; i < length; i += BYTES_PER_LINE) {
        int n = snprintf(line, 9, "%04x", i);
        for (int j = i; j < i + BYTES_PER_LINE && j < length; j++)
            n += snprintf(line + n, 4, " %02x", buffer[j]);
        LOG_DEBUG("%s", line);
 
        /* Prevent GDB timeout (writing to log might take some time) */
        keep_alive();
    }
}
#endif