src/jtag/drivers/bitbang.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2
   3 /***************************************************************************
   4  *   Copyright (C) 2005 by Dominic Rath                                    *
   5  *   Dominic.Rath@gmx.de                                                   *
   6  *                                                                         *
   7  *   Copyright (C) 2007,2008 Øyvind Harboe                                 *
   8  *   oyvind.harboe@zylin.com                                               *
   9  ***************************************************************************/
  10
  11 /* 2014-12: Addition of the SWD protocol support is based on the initial work
  12  * by Paul Fertser and modifications by Jean-Christian de Rivaz. */
  13
  14 #ifdef HAVE_CONFIG_H
  15 #include "config.h"
  16 #endif
  17
  18 #include "bitbang.h"
  19 #include <jtag/interface.h>
  20 #include <jtag/commands.h>
  21
  22 /**
  23  * Function bitbang_stableclocks
  24  * issues a number of clock cycles while staying in a stable state.
  25  * Because the TMS value required to stay in the RESET state is a 1, whereas
  26  * the TMS value required to stay in any of the other stable states is a 0,
  27  * this function checks the current stable state to decide on the value of TMS
  28  * to use.
  29  */
  30 static int bitbang_stableclocks(int num_cycles);
  31
  32 static void bitbang_swd_write_reg(uint8_t cmd, uint32_t value, uint32_t ap_delay_clk);
  33
  34 struct bitbang_interface *bitbang_interface;
  35
  36 /* DANGER!!!! clock absolutely *MUST* be 0 in idle or reset won't work!
  37  *
  38  * Set this to 1 and str912 reset halt will fail.
  39  *
  40  * If someone can submit a patch with an explanation it will be greatly
  41  * appreciated, but as far as I can tell (ØH) DCLK is generated upon
  42  * clk = 0 in TAP_IDLE. Good luck deducing that from the ARM documentation!
  43  * The ARM documentation uses the term "DCLK is asserted while in the TAP_IDLE
  44  * state". With hardware there is no such thing as *while* in a state. There
  45  * are only edges. So clk => 0 is in fact a very subtle state transition that
  46  * happens *while* in the TAP_IDLE state. "#&¤"#¤&"#&"#&
  47  *
  48  * For "reset halt" the last thing that happens before srst is asserted
  49  * is that the breakpoint is set up. If DCLK is not wiggled one last
  50  * time before the reset, then the breakpoint is not set up and
  51  * "reset halt" will fail to halt.
  52  *
  53  */
  54 #define CLOCK_IDLE() 0
  55
  56 /* The bitbang driver leaves the TCK 0 when in idle */
  57 static void bitbang_end_state(tap_state_t state)
  58 {
  59         assert(tap_is_state_stable(state));
  60         tap_set_end_state(state);
  61 }
  62
  63 static int bitbang_state_move(int skip)
  64 {
  65         int i = 0, tms = 0;
  66         uint8_t tms_scan = tap_get_tms_path(tap_get_state(), tap_get_end_state());
  67         int tms_count = tap_get_tms_path_len(tap_get_state(), tap_get_end_state());
  68
  69         for (i = skip; i < tms_count; i++) {
  70                 tms = (tms_scan >> i) & 1;
  71                 if (bitbang_interface->write(0, tms, 0) != ERROR_OK)
  72                         return ERROR_FAIL;
  73                 if (bitbang_interface->write(1, tms, 0) != ERROR_OK)
  74                         return ERROR_FAIL;
  75         }
  76         if (bitbang_interface->write(CLOCK_IDLE(), tms, 0) != ERROR_OK)
  77                 return ERROR_FAIL;
  78
  79         tap_set_state(tap_get_end_state());
  80         return ERROR_OK;
  81 }
  82
  83 /**
  84  * Clock a bunch of TMS (or SWDIO) transitions, to change the JTAG
  85  * (or SWD) state machine.
  86  */
  87 static int bitbang_execute_tms(struct jtag_command *cmd)
  88 {
  89         unsigned num_bits = cmd->cmd.tms->num_bits;
  90         const uint8_t *bits = cmd->cmd.tms->bits;
  91
  92         LOG_DEBUG_IO("TMS: %d bits", num_bits);
  93
  94         int tms = 0;
  95         for (unsigned i = 0; i < num_bits; i++) {
  96                 tms = ((bits[i/8] >> (i % 8)) & 1);
  97                 if (bitbang_interface->write(0, tms, 0) != ERROR_OK)
  98                         return ERROR_FAIL;
  99                 if (bitbang_interface->write(1, tms, 0) != ERROR_OK)
 100                         return ERROR_FAIL;
 101         }
 102         if (bitbang_interface->write(CLOCK_IDLE(), tms, 0) != ERROR_OK)
 103                 return ERROR_FAIL;
 104
 105         return ERROR_OK;
 106 }
 107
 108 static int bitbang_path_move(struct pathmove_command *cmd)
 109 {
 110         int num_states = cmd->num_states;
 111         int state_count;
 112         int tms = 0;
 113
 114         state_count = 0;
 115         while (num_states) {
 116                 if (tap_state_transition(tap_get_state(), false) == cmd->path[state_count])
 117                         tms = 0;
 118                 else if (tap_state_transition(tap_get_state(), true) == cmd->path[state_count])
 119                         tms = 1;
 120                 else {
 121                         LOG_ERROR("BUG: %s -> %s isn't a valid TAP transition",
 122                                 tap_state_name(tap_get_state()),
 123                                 tap_state_name(cmd->path[state_count]));
 124                         exit(-1);
 125                 }
 126
 127                 if (bitbang_interface->write(0, tms, 0) != ERROR_OK)
 128                         return ERROR_FAIL;
 129                 if (bitbang_interface->write(1, tms, 0) != ERROR_OK)
 130                         return ERROR_FAIL;
 131
 132                 tap_set_state(cmd->path[state_count]);
 133                 state_count++;
 134                 num_states--;
 135         }
 136
 137         if (bitbang_interface->write(CLOCK_IDLE(), tms, 0) != ERROR_OK)
 138                 return ERROR_FAIL;
 139
 140         tap_set_end_state(tap_get_state());
 141         return ERROR_OK;
 142 }
 143
 144 static int bitbang_runtest(int num_cycles)
 145 {
 146         int i;
 147
 148         tap_state_t saved_end_state = tap_get_end_state();
 149
 150         /* only do a state_move when we're not already in IDLE */
 151         if (tap_get_state() != TAP_IDLE) {
 152                 bitbang_end_state(TAP_IDLE);
 153                 if (bitbang_state_move(0) != ERROR_OK)
 154                         return ERROR_FAIL;
 155         }
 156
 157         /* execute num_cycles */
 158         for (i = 0; i < num_cycles; i++) {
 159                 if (bitbang_interface->write(0, 0, 0) != ERROR_OK)
 160                         return ERROR_FAIL;
 161                 if (bitbang_interface->write(1, 0, 0) != ERROR_OK)
 162                         return ERROR_FAIL;
 163         }
 164         if (bitbang_interface->write(CLOCK_IDLE(), 0, 0) != ERROR_OK)
 165                 return ERROR_FAIL;
 166
 167         /* finish in end_state */
 168         bitbang_end_state(saved_end_state);
 169         if (tap_get_state() != tap_get_end_state())
 170                 if (bitbang_state_move(0) != ERROR_OK)
 171                         return ERROR_FAIL;
 172
 173         return ERROR_OK;
 174 }
 175
 176 static int bitbang_stableclocks(int num_cycles)
 177 {
 178         int tms = (tap_get_state() == TAP_RESET ? 1 : 0);
 179         int i;
 180
 181         /* send num_cycles clocks onto the cable */
 182         for (i = 0; i < num_cycles; i++) {
 183                 if (bitbang_interface->write(1, tms, 0) != ERROR_OK)
 184                         return ERROR_FAIL;
 185                 if (bitbang_interface->write(0, tms, 0) != ERROR_OK)
 186                         return ERROR_FAIL;
 187         }
 188
 189         return ERROR_OK;
 190 }
 191
 192 static int bitbang_scan(bool ir_scan, enum scan_type type, uint8_t *buffer,
 193                 unsigned scan_size)
 194 {
 195         tap_state_t saved_end_state = tap_get_end_state();
 196         unsigned bit_cnt;
 197
 198         if (!((!ir_scan &&
 199                         (tap_get_state() == TAP_DRSHIFT)) ||
 200                         (ir_scan && (tap_get_state() == TAP_IRSHIFT)))) {
 201                 if (ir_scan)
 202                         bitbang_end_state(TAP_IRSHIFT);
 203                 else
 204                         bitbang_end_state(TAP_DRSHIFT);
 205
 206                 if (bitbang_state_move(0) != ERROR_OK)
 207                         return ERROR_FAIL;
 208                 bitbang_end_state(saved_end_state);
 209         }
 210
 211         size_t buffered = 0;
 212         for (bit_cnt = 0; bit_cnt < scan_size; bit_cnt++) {
 213                 int tms = (bit_cnt == scan_size-1) ? 1 : 0;
 214                 int tdi;
 215                 int bytec = bit_cnt/8;
 216                 int bcval = 1 << (bit_cnt % 8);
 217
 218                 /* if we're just reading the scan, but don't care about the output
 219                  * default to outputting 'low', this also makes valgrind traces more readable,
 220                  * as it removes the dependency on an uninitialised value
 221                  */
 222                 tdi = 0;
 223                 if ((type != SCAN_IN) && (buffer[bytec] & bcval))
 224                         tdi = 1;
 225
 226                 if (bitbang_interface->write(0, tms, tdi) != ERROR_OK)
 227                         return ERROR_FAIL;
 228
 229                 if (type != SCAN_OUT) {
 230                         if (bitbang_interface->buf_size) {
 231                                 if (bitbang_interface->sample() != ERROR_OK)
 232                                         return ERROR_FAIL;
 233                                 buffered++;
 234                         } else {
 235                                 switch (bitbang_interface->read()) {
 236                                         case BB_LOW:
 237                                                 buffer[bytec] &= ~bcval;
 238                                                 break;
 239                                         case BB_HIGH:
 240                                                 buffer[bytec] |= bcval;
 241                                                 break;
 242                                         default:
 243                                                 return ERROR_FAIL;
 244                                 }
 245                         }
 246                 }
 247
 248                 if (bitbang_interface->write(1, tms, tdi) != ERROR_OK)
 249                         return ERROR_FAIL;
 250
 251                 if (type != SCAN_OUT && bitbang_interface->buf_size &&
 252                                 (buffered == bitbang_interface->buf_size ||
 253                                  bit_cnt == scan_size - 1)) {
 254                         for (unsigned i = bit_cnt + 1 - buffered; i <= bit_cnt; i++) {
 255                                 switch (bitbang_interface->read_sample()) {
 256                                         case BB_LOW:
 257                                                 buffer[i/8] &= ~(1 << (i % 8));
 258                                                 break;
 259                                         case BB_HIGH:
 260                                                 buffer[i/8] |= 1 << (i % 8);
 261                                                 break;
 262                                         default:
 263                                                 return ERROR_FAIL;
 264                                 }
 265                         }
 266                         buffered = 0;
 267                 }
 268         }
 269
 270         if (tap_get_state() != tap_get_end_state()) {
 271                 /* we *KNOW* the above loop transitioned out of
 272                  * the shift state, so we skip the first state
 273                  * and move directly to the end state.
 274                  */
 275                 if (bitbang_state_move(1) != ERROR_OK)
 276                         return ERROR_FAIL;
 277         }
 278         return ERROR_OK;
 279 }
 280
 281 int bitbang_execute_queue(void)
 282 {
 283         struct jtag_command *cmd = jtag_command_queue;  /* currently processed command */
 284         int scan_size;
 285         enum scan_type type;
 286         uint8_t *buffer;
 287         int retval;
 288
 289         if (!bitbang_interface) {
 290                 LOG_ERROR("BUG: Bitbang interface called, but not yet initialized");
 291                 exit(-1);
 292         }
 293
 294         /* return ERROR_OK, unless a jtag_read_buffer returns a failed check
 295          * that wasn't handled by a caller-provided error handler
 296          */
 297         retval = ERROR_OK;
 298
 299         if (bitbang_interface->blink) {
 300                 if (bitbang_interface->blink(1) != ERROR_OK)
 301                         return ERROR_FAIL;
 302         }
 303
 304         while (cmd) {
 305                 switch (cmd->type) {
 306                         case JTAG_RUNTEST:
 307                                 LOG_DEBUG_IO("runtest %i cycles, end in %s",
 308                                                 cmd->cmd.runtest->num_cycles,
 309                                                 tap_state_name(cmd->cmd.runtest->end_state));
 310                                 bitbang_end_state(cmd->cmd.runtest->end_state);
 311                                 if (bitbang_runtest(cmd->cmd.runtest->num_cycles) != ERROR_OK)
 312                                         return ERROR_FAIL;
 313                                 break;
 314
 315                         case JTAG_STABLECLOCKS:
 316                                 /* this is only allowed while in a stable state.  A check for a stable
 317                                  * state was done in jtag_add_clocks()
 318                                  */
 319                                 if (bitbang_stableclocks(cmd->cmd.stableclocks->num_cycles) != ERROR_OK)
 320                                         return ERROR_FAIL;
 321                                 break;
 322
 323                         case JTAG_TLR_RESET:
 324                                 LOG_DEBUG_IO("statemove end in %s",
 325                                                 tap_state_name(cmd->cmd.statemove->end_state));
 326                                 bitbang_end_state(cmd->cmd.statemove->end_state);
 327                                 if (bitbang_state_move(0) != ERROR_OK)
 328                                         return ERROR_FAIL;
 329                                 break;
 330                         case JTAG_PATHMOVE:
 331                                 LOG_DEBUG_IO("pathmove: %i states, end in %s",
 332                                                 cmd->cmd.pathmove->num_states,
 333                                                 tap_state_name(cmd->cmd.pathmove->path[cmd->cmd.pathmove->num_states - 1]));
 334                                 if (bitbang_path_move(cmd->cmd.pathmove) != ERROR_OK)
 335                                         return ERROR_FAIL;
 336                                 break;
 337                         case JTAG_SCAN:
 338                                 bitbang_end_state(cmd->cmd.scan->end_state);
 339                                 scan_size = jtag_build_buffer(cmd->cmd.scan, &buffer);
 340                                 LOG_DEBUG_IO("%s scan %d bits; end in %s",
 341                                                 (cmd->cmd.scan->ir_scan) ? "IR" : "DR",
 342                                                 scan_size,
 343                                         tap_state_name(cmd->cmd.scan->end_state));
 344                                 type = jtag_scan_type(cmd->cmd.scan);
 345                                 if (bitbang_scan(cmd->cmd.scan->ir_scan, type, buffer,
 346                                                         scan_size) != ERROR_OK)
 347                                         return ERROR_FAIL;
 348                                 if (jtag_read_buffer(buffer, cmd->cmd.scan) != ERROR_OK)
 349                                         retval = ERROR_JTAG_QUEUE_FAILED;
 350                                 free(buffer);
 351                                 break;
 352                         case JTAG_SLEEP:
 353                                 LOG_DEBUG_IO("sleep %" PRIu32, cmd->cmd.sleep->us);
 354                                 jtag_sleep(cmd->cmd.sleep->us);
 355                                 break;
 356                         case JTAG_TMS:
 357                                 retval = bitbang_execute_tms(cmd);
 358                                 break;
 359                         default:
 360                                 LOG_ERROR("BUG: unknown JTAG command type encountered");
 361                                 exit(-1);
 362                 }
 363                 cmd = cmd->next;
 364         }
 365         if (bitbang_interface->blink) {
 366                 if (bitbang_interface->blink(0) != ERROR_OK)
 367                         return ERROR_FAIL;
 368         }
 369
 370         return retval;
 371 }
 372
 373 static int queued_retval;
 374
 375 static int bitbang_swd_init(void)
 376 {
 377         LOG_DEBUG("bitbang_swd_init");
 378         return ERROR_OK;
 379 }
 380
 381 static void bitbang_swd_exchange(bool rnw, uint8_t buf[], unsigned int offset, unsigned int bit_cnt)
 382 {
 383         if (bitbang_interface->blink) {
 384                 /* FIXME: we should manage errors */
 385                 bitbang_interface->blink(1);
 386         }
 387
 388         for (unsigned int i = offset; i < bit_cnt + offset; i++) {
 389                 int bytec = i/8;
 390                 int bcval = 1 << (i % 8);
 391                 int swdio = !rnw && (buf[bytec] & bcval);
 392
 393                 bitbang_interface->swd_write(0, swdio);
 394
 395                 if (rnw && buf) {
 396                         if (bitbang_interface->swdio_read())
 397                                 buf[bytec] |= bcval;
 398                         else
 399                                 buf[bytec] &= ~bcval;
 400                 }
 401
 402                 bitbang_interface->swd_write(1, swdio);
 403         }
 404
 405         if (bitbang_interface->blink) {
 406                 /* FIXME: we should manage errors */
 407                 bitbang_interface->blink(0);
 408         }
 409 }
 410
 411 static int bitbang_swd_switch_seq(enum swd_special_seq seq)
 412 {
 413         switch (seq) {
 414         case LINE_RESET:
 415                 LOG_DEBUG_IO("SWD line reset");
 416                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_line_reset, 0, swd_seq_line_reset_len);
 417                 break;
 418         case JTAG_TO_SWD:
 419                 LOG_DEBUG("JTAG-to-SWD");
 420                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_jtag_to_swd, 0, swd_seq_jtag_to_swd_len);
 421                 break;
 422         case JTAG_TO_DORMANT:
 423                 LOG_DEBUG("JTAG-to-DORMANT");
 424                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_jtag_to_dormant, 0, swd_seq_jtag_to_dormant_len);
 425                 break;
 426         case SWD_TO_JTAG:
 427                 LOG_DEBUG("SWD-to-JTAG");
 428                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_swd_to_jtag, 0, swd_seq_swd_to_jtag_len);
 429                 break;
 430         case SWD_TO_DORMANT:
 431                 LOG_DEBUG("SWD-to-DORMANT");
 432                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_swd_to_dormant, 0, swd_seq_swd_to_dormant_len);
 433                 break;
 434         case DORMANT_TO_SWD:
 435                 LOG_DEBUG("DORMANT-to-SWD");
 436                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_dormant_to_swd, 0, swd_seq_dormant_to_swd_len);
 437                 break;
 438         case DORMANT_TO_JTAG:
 439                 LOG_DEBUG("DORMANT-to-JTAG");
 440                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_dormant_to_jtag, 0, swd_seq_dormant_to_jtag_len);
 441                 break;
 442         default:
 443                 LOG_ERROR("Sequence %d not supported", seq);
 444                 return ERROR_FAIL;
 445         }
 446
 447         return ERROR_OK;
 448 }
 449
 450 static void swd_clear_sticky_errors(void)
 451 {
 452         bitbang_swd_write_reg(swd_cmd(false,  false, DP_ABORT),
 453                 STKCMPCLR | STKERRCLR | WDERRCLR | ORUNERRCLR, 0);
 454 }
 455
 456 static void bitbang_swd_read_reg(uint8_t cmd, uint32_t *value, uint32_t ap_delay_clk)
 457 {
 458         assert(cmd & SWD_CMD_RNW);
 459
 460         if (queued_retval != ERROR_OK) {
 461                 LOG_DEBUG("Skip bitbang_swd_read_reg because queued_retval=%d", queued_retval);
 462                 return;
 463         }
 464
 465         for (;;) {
 466                 uint8_t trn_ack_data_parity_trn[DIV_ROUND_UP(4 + 3 + 32 + 1 + 4, 8)];
 467
 468                 cmd |= SWD_CMD_START | SWD_CMD_PARK;
 469                 bitbang_swd_exchange(false, &cmd, 0, 8);
 470
 471                 bitbang_interface->swdio_drive(false);
 472                 bitbang_swd_exchange(true, trn_ack_data_parity_trn, 0, 1 + 3 + 32 + 1 + 1);
 473                 bitbang_interface->swdio_drive(true);
 474
 475                 int ack = buf_get_u32(trn_ack_data_parity_trn, 1, 3);
 476                 uint32_t data = buf_get_u32(trn_ack_data_parity_trn, 1 + 3, 32);
 477                 int parity = buf_get_u32(trn_ack_data_parity_trn, 1 + 3 + 32, 1);
 478
 479                 LOG_DEBUG_IO("%s %s read reg %X = %08" PRIx32,
 480                           ack == SWD_ACK_OK ? "OK" : ack == SWD_ACK_WAIT ? "WAIT" : ack == SWD_ACK_FAULT ? "FAULT" : "JUNK",
 481                           cmd & SWD_CMD_APNDP ? "AP" : "DP",
 482                           (cmd & SWD_CMD_A32) >> 1,
 483                           data);
 484
 485                 if (ack == SWD_ACK_WAIT) {
 486                         swd_clear_sticky_errors();
 487                         continue;
 488                 } else if (ack != SWD_ACK_OK) {
 489                         queued_retval = swd_ack_to_error_code(ack);
 490                         return;
 491                 }
 492
 493                 if (parity != parity_u32(data)) {
 494                         LOG_ERROR("Wrong parity detected");
 495                         queued_retval = ERROR_FAIL;
 496                         return;
 497                 }
 498                 if (value)
 499                         *value = data;
 500                 if (cmd & SWD_CMD_APNDP)
 501                         bitbang_swd_exchange(true, NULL, 0, ap_delay_clk);
 502                 return;
 503         }
 504 }
 505
 506 static void bitbang_swd_write_reg(uint8_t cmd, uint32_t value, uint32_t ap_delay_clk)
 507 {
 508         assert(!(cmd & SWD_CMD_RNW));
 509
 510         if (queued_retval != ERROR_OK) {
 511                 LOG_DEBUG("Skip bitbang_swd_write_reg because queued_retval=%d", queued_retval);
 512                 return;
 513         }
 514
 515         /* Devices do not reply to DP_TARGETSEL write cmd, ignore received ack */
 516         bool check_ack = swd_cmd_returns_ack(cmd);
 517
 518         /* init the array to silence scan-build */
 519         uint8_t trn_ack_data_parity_trn[DIV_ROUND_UP(4 + 3 + 32 + 1 + 4, 8)] = {0};
 520         for (;;) {
 521                 buf_set_u32(trn_ack_data_parity_trn, 1 + 3 + 1, 32, value);
 522                 buf_set_u32(trn_ack_data_parity_trn, 1 + 3 + 1 + 32, 1, parity_u32(value));
 523
 524                 cmd |= SWD_CMD_START | SWD_CMD_PARK;
 525                 bitbang_swd_exchange(false, &cmd, 0, 8);
 526
 527                 bitbang_interface->swdio_drive(false);
 528                 bitbang_swd_exchange(true, trn_ack_data_parity_trn, 0, 1 + 3);
 529
 530                 /* Avoid a glitch on SWDIO when changing the direction to output.
 531                  * To keep performance penalty minimal, pre-write the first data
 532                  * bit to SWDIO GPIO output buffer while clocking the turnaround bit.
 533                  * Following swdio_drive(true) outputs the pre-written value
 534                  * and the same value is rewritten by the next swd_write()
 535                  * instead of glitching SWDIO
 536                  * HiZ/pull-up --------------> 0 -------------> 1
 537                  *           swdio_drive(true)   swd_write(0,1)
 538                  * in case of data bit 0 = 1
 539                  */
 540                 bitbang_swd_exchange(false, trn_ack_data_parity_trn, 1 + 3 + 1, 1);
 541                 bitbang_interface->swdio_drive(true);
 542                 bitbang_swd_exchange(false, trn_ack_data_parity_trn, 1 + 3 + 1, 32 + 1);
 543
 544                 int ack = buf_get_u32(trn_ack_data_parity_trn, 1, 3);
 545
 546                 LOG_DEBUG_IO("%s%s %s write reg %X = %08" PRIx32,
 547                           check_ack ? "" : "ack ignored ",
 548                           ack == SWD_ACK_OK ? "OK" : ack == SWD_ACK_WAIT ? "WAIT" : ack == SWD_ACK_FAULT ? "FAULT" : "JUNK",
 549                           cmd & SWD_CMD_APNDP ? "AP" : "DP",
 550                           (cmd & SWD_CMD_A32) >> 1,
 551                           buf_get_u32(trn_ack_data_parity_trn, 1 + 3 + 1, 32));
 552
 553                 if (check_ack) {
 554                         if (ack == SWD_ACK_WAIT) {
 555                                 swd_clear_sticky_errors();
 556                                 continue;
 557                         } else if (ack != SWD_ACK_OK) {
 558                                 queued_retval = swd_ack_to_error_code(ack);
 559                                 return;
 560                         }
 561                 }
 562
 563                 if (cmd & SWD_CMD_APNDP)
 564                         bitbang_swd_exchange(true, NULL, 0, ap_delay_clk);
 565                 return;
 566         }
 567 }
 568
 569 static int bitbang_swd_run_queue(void)
 570 {
 571         /* A transaction must be followed by another transaction or at least 8 idle cycles to
 572          * ensure that data is clocked through the AP. */
 573         bitbang_swd_exchange(true, NULL, 0, 8);
 574
 575         int retval = queued_retval;
 576         queued_retval = ERROR_OK;
 577         LOG_DEBUG_IO("SWD queue return value: %02x", retval);
 578         return retval;
 579 }
 580
 581 const struct swd_driver bitbang_swd = {
 582         .init = bitbang_swd_init,
 583         .switch_seq = bitbang_swd_switch_seq,
 584         .read_reg = bitbang_swd_read_reg,
 585         .write_reg = bitbang_swd_write_reg,
 586         .run = bitbang_swd_run_queue,
 587 };