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 <jtag/jtag.h>      /* Added to avoid include loop in commands.h */
  19 #include "bitbang.h"
  20 #include <jtag/interface.h>
  21 #include <jtag/commands.h>
  22
  23 #include <helper/time_support.h>
  24
  25 /* Timeout for retrying on SWD WAIT in msec */
  26 #define SWD_WAIT_TIMEOUT 500
  27
  28 /**
  29  * Function bitbang_stableclocks
  30  * issues a number of clock cycles while staying in a stable state.
  31  * Because the TMS value required to stay in the RESET state is a 1, whereas
  32  * the TMS value required to stay in any of the other stable states is a 0,
  33  * this function checks the current stable state to decide on the value of TMS
  34  * to use.
  35  */
  36 static int bitbang_stableclocks(int num_cycles);
  37
  38 static void bitbang_swd_write_reg(uint8_t cmd, uint32_t value, uint32_t ap_delay_clk);
  39
  40 struct bitbang_interface *bitbang_interface;
  41
  42 /* DANGER!!!! clock absolutely *MUST* be 0 in idle or reset won't work!
  43  *
  44  * Set this to 1 and str912 reset halt will fail.
  45  *
  46  * If someone can submit a patch with an explanation it will be greatly
  47  * appreciated, but as far as I can tell (ØH) DCLK is generated upon
  48  * clk = 0 in TAP_IDLE. Good luck deducing that from the ARM documentation!
  49  * The ARM documentation uses the term "DCLK is asserted while in the TAP_IDLE
  50  * state". With hardware there is no such thing as *while* in a state. There
  51  * are only edges. So clk => 0 is in fact a very subtle state transition that
  52  * happens *while* in the TAP_IDLE state. "#&¤"#¤&"#&"#&
  53  *
  54  * For "reset halt" the last thing that happens before srst is asserted
  55  * is that the breakpoint is set up. If DCLK is not wiggled one last
  56  * time before the reset, then the breakpoint is not set up and
  57  * "reset halt" will fail to halt.
  58  *
  59  */
  60 #define CLOCK_IDLE() 0
  61
  62 /* The bitbang driver leaves the TCK 0 when in idle */
  63 static void bitbang_end_state(tap_state_t state)
  64 {
  65         assert(tap_is_state_stable(state));
  66         tap_set_end_state(state);
  67 }
  68
  69 static int bitbang_state_move(int skip)
  70 {
  71         int i = 0, tms = 0;
  72         uint8_t tms_scan = tap_get_tms_path(tap_get_state(), tap_get_end_state());
  73         int tms_count = tap_get_tms_path_len(tap_get_state(), tap_get_end_state());
  74
  75         for (i = skip; i < tms_count; i++) {
  76                 tms = (tms_scan >> i) & 1;
  77                 if (bitbang_interface->write(0, tms, 0) != ERROR_OK)
  78                         return ERROR_FAIL;
  79                 if (bitbang_interface->write(1, tms, 0) != ERROR_OK)
  80                         return ERROR_FAIL;
  81         }
  82         if (bitbang_interface->write(CLOCK_IDLE(), tms, 0) != ERROR_OK)
  83                 return ERROR_FAIL;
  84
  85         tap_set_state(tap_get_end_state());
  86         return ERROR_OK;
  87 }
  88
  89 /**
  90  * Clock a bunch of TMS (or SWDIO) transitions, to change the JTAG
  91  * (or SWD) state machine.
  92  */
  93 static int bitbang_execute_tms(struct jtag_command *cmd)
  94 {
  95         unsigned num_bits = cmd->cmd.tms->num_bits;
  96         const uint8_t *bits = cmd->cmd.tms->bits;
  97
  98         LOG_DEBUG_IO("TMS: %d bits", num_bits);
  99
 100         int tms = 0;
 101         for (unsigned i = 0; i < num_bits; i++) {
 102                 tms = ((bits[i/8] >> (i % 8)) & 1);
 103                 if (bitbang_interface->write(0, tms, 0) != ERROR_OK)
 104                         return ERROR_FAIL;
 105                 if (bitbang_interface->write(1, tms, 0) != ERROR_OK)
 106                         return ERROR_FAIL;
 107         }
 108         if (bitbang_interface->write(CLOCK_IDLE(), tms, 0) != ERROR_OK)
 109                 return ERROR_FAIL;
 110
 111         return ERROR_OK;
 112 }
 113
 114 static int bitbang_path_move(struct pathmove_command *cmd)
 115 {
 116         int num_states = cmd->num_states;
 117         int state_count;
 118         int tms = 0;
 119
 120         state_count = 0;
 121         while (num_states) {
 122                 if (tap_state_transition(tap_get_state(), false) == cmd->path[state_count])
 123                         tms = 0;
 124                 else if (tap_state_transition(tap_get_state(), true) == cmd->path[state_count])
 125                         tms = 1;
 126                 else {
 127                         LOG_ERROR("BUG: %s -> %s isn't a valid TAP transition",
 128                                 tap_state_name(tap_get_state()),
 129                                 tap_state_name(cmd->path[state_count]));
 130                         exit(-1);
 131                 }
 132
 133                 if (bitbang_interface->write(0, tms, 0) != ERROR_OK)
 134                         return ERROR_FAIL;
 135                 if (bitbang_interface->write(1, tms, 0) != ERROR_OK)
 136                         return ERROR_FAIL;
 137
 138                 tap_set_state(cmd->path[state_count]);
 139                 state_count++;
 140                 num_states--;
 141         }
 142
 143         if (bitbang_interface->write(CLOCK_IDLE(), tms, 0) != ERROR_OK)
 144                 return ERROR_FAIL;
 145
 146         tap_set_end_state(tap_get_state());
 147         return ERROR_OK;
 148 }
 149
 150 static int bitbang_runtest(int num_cycles)
 151 {
 152         int i;
 153
 154         tap_state_t saved_end_state = tap_get_end_state();
 155
 156         /* only do a state_move when we're not already in IDLE */
 157         if (tap_get_state() != TAP_IDLE) {
 158                 bitbang_end_state(TAP_IDLE);
 159                 if (bitbang_state_move(0) != ERROR_OK)
 160                         return ERROR_FAIL;
 161         }
 162
 163         /* execute num_cycles */
 164         for (i = 0; i < num_cycles; i++) {
 165                 if (bitbang_interface->write(0, 0, 0) != ERROR_OK)
 166                         return ERROR_FAIL;
 167                 if (bitbang_interface->write(1, 0, 0) != ERROR_OK)
 168                         return ERROR_FAIL;
 169         }
 170         if (bitbang_interface->write(CLOCK_IDLE(), 0, 0) != ERROR_OK)
 171                 return ERROR_FAIL;
 172
 173         /* finish in end_state */
 174         bitbang_end_state(saved_end_state);
 175         if (tap_get_state() != tap_get_end_state())
 176                 if (bitbang_state_move(0) != ERROR_OK)
 177                         return ERROR_FAIL;
 178
 179         return ERROR_OK;
 180 }
 181
 182 static int bitbang_stableclocks(int num_cycles)
 183 {
 184         int tms = (tap_get_state() == TAP_RESET ? 1 : 0);
 185         int i;
 186
 187         /* send num_cycles clocks onto the cable */
 188         for (i = 0; i < num_cycles; i++) {
 189                 if (bitbang_interface->write(1, tms, 0) != ERROR_OK)
 190                         return ERROR_FAIL;
 191                 if (bitbang_interface->write(0, tms, 0) != ERROR_OK)
 192                         return ERROR_FAIL;
 193         }
 194
 195         return ERROR_OK;
 196 }
 197
 198 static int bitbang_scan(bool ir_scan, enum scan_type type, uint8_t *buffer,
 199                 unsigned scan_size)
 200 {
 201         tap_state_t saved_end_state = tap_get_end_state();
 202         unsigned bit_cnt;
 203
 204         if (!((!ir_scan &&
 205                         (tap_get_state() == TAP_DRSHIFT)) ||
 206                         (ir_scan && (tap_get_state() == TAP_IRSHIFT)))) {
 207                 if (ir_scan)
 208                         bitbang_end_state(TAP_IRSHIFT);
 209                 else
 210                         bitbang_end_state(TAP_DRSHIFT);
 211
 212                 if (bitbang_state_move(0) != ERROR_OK)
 213                         return ERROR_FAIL;
 214                 bitbang_end_state(saved_end_state);
 215         }
 216
 217         size_t buffered = 0;
 218         for (bit_cnt = 0; bit_cnt < scan_size; bit_cnt++) {
 219                 int tms = (bit_cnt == scan_size-1) ? 1 : 0;
 220                 int tdi;
 221                 int bytec = bit_cnt/8;
 222                 int bcval = 1 << (bit_cnt % 8);
 223
 224                 /* if we're just reading the scan, but don't care about the output
 225                  * default to outputting 'low', this also makes valgrind traces more readable,
 226                  * as it removes the dependency on an uninitialised value
 227                  */
 228                 tdi = 0;
 229                 if ((type != SCAN_IN) && (buffer[bytec] & bcval))
 230                         tdi = 1;
 231
 232                 if (bitbang_interface->write(0, tms, tdi) != ERROR_OK)
 233                         return ERROR_FAIL;
 234
 235                 if (type != SCAN_OUT) {
 236                         if (bitbang_interface->buf_size) {
 237                                 if (bitbang_interface->sample() != ERROR_OK)
 238                                         return ERROR_FAIL;
 239                                 buffered++;
 240                         } else {
 241                                 switch (bitbang_interface->read()) {
 242                                         case BB_LOW:
 243                                                 buffer[bytec] &= ~bcval;
 244                                                 break;
 245                                         case BB_HIGH:
 246                                                 buffer[bytec] |= bcval;
 247                                                 break;
 248                                         default:
 249                                                 return ERROR_FAIL;
 250                                 }
 251                         }
 252                 }
 253
 254                 if (bitbang_interface->write(1, tms, tdi) != ERROR_OK)
 255                         return ERROR_FAIL;
 256
 257                 if (type != SCAN_OUT && bitbang_interface->buf_size &&
 258                                 (buffered == bitbang_interface->buf_size ||
 259                                  bit_cnt == scan_size - 1)) {
 260                         for (unsigned i = bit_cnt + 1 - buffered; i <= bit_cnt; i++) {
 261                                 switch (bitbang_interface->read_sample()) {
 262                                         case BB_LOW:
 263                                                 buffer[i/8] &= ~(1 << (i % 8));
 264                                                 break;
 265                                         case BB_HIGH:
 266                                                 buffer[i/8] |= 1 << (i % 8);
 267                                                 break;
 268                                         default:
 269                                                 return ERROR_FAIL;
 270                                 }
 271                         }
 272                         buffered = 0;
 273                 }
 274         }
 275
 276         if (tap_get_state() != tap_get_end_state()) {
 277                 /* we *KNOW* the above loop transitioned out of
 278                  * the shift state, so we skip the first state
 279                  * and move directly to the end state.
 280                  */
 281                 if (bitbang_state_move(1) != ERROR_OK)
 282                         return ERROR_FAIL;
 283         }
 284         return ERROR_OK;
 285 }
 286
 287 static void bitbang_sleep(unsigned int microseconds)
 288 {
 289         if (bitbang_interface->sleep) {
 290                 bitbang_interface->sleep(microseconds);
 291         } else {
 292                 jtag_sleep(microseconds);
 293         }
 294 }
 295
 296 int bitbang_execute_queue(struct jtag_command *cmd_queue)
 297 {
 298         struct jtag_command *cmd = cmd_queue;   /* currently processed command */
 299         int scan_size;
 300         enum scan_type type;
 301         uint8_t *buffer;
 302         int retval;
 303
 304         if (!bitbang_interface) {
 305                 LOG_ERROR("BUG: Bitbang interface called, but not yet initialized");
 306                 exit(-1);
 307         }
 308
 309         /* return ERROR_OK, unless a jtag_read_buffer returns a failed check
 310          * that wasn't handled by a caller-provided error handler
 311          */
 312         retval = ERROR_OK;
 313
 314         if (bitbang_interface->blink) {
 315                 if (bitbang_interface->blink(1) != ERROR_OK)
 316                         return ERROR_FAIL;
 317         }
 318
 319         while (cmd) {
 320                 switch (cmd->type) {
 321                         case JTAG_RUNTEST:
 322                                 LOG_DEBUG_IO("runtest %i cycles, end in %s",
 323                                                 cmd->cmd.runtest->num_cycles,
 324                                                 tap_state_name(cmd->cmd.runtest->end_state));
 325                                 bitbang_end_state(cmd->cmd.runtest->end_state);
 326                                 if (bitbang_runtest(cmd->cmd.runtest->num_cycles) != ERROR_OK)
 327                                         return ERROR_FAIL;
 328                                 break;
 329
 330                         case JTAG_STABLECLOCKS:
 331                                 /* this is only allowed while in a stable state.  A check for a stable
 332                                  * state was done in jtag_add_clocks()
 333                                  */
 334                                 if (bitbang_stableclocks(cmd->cmd.stableclocks->num_cycles) != ERROR_OK)
 335                                         return ERROR_FAIL;
 336                                 break;
 337
 338                         case JTAG_TLR_RESET:
 339                                 LOG_DEBUG_IO("statemove end in %s",
 340                                                 tap_state_name(cmd->cmd.statemove->end_state));
 341                                 bitbang_end_state(cmd->cmd.statemove->end_state);
 342                                 if (bitbang_state_move(0) != ERROR_OK)
 343                                         return ERROR_FAIL;
 344                                 break;
 345                         case JTAG_PATHMOVE:
 346                                 LOG_DEBUG_IO("pathmove: %i states, end in %s",
 347                                                 cmd->cmd.pathmove->num_states,
 348                                                 tap_state_name(cmd->cmd.pathmove->path[cmd->cmd.pathmove->num_states - 1]));
 349                                 if (bitbang_path_move(cmd->cmd.pathmove) != ERROR_OK)
 350                                         return ERROR_FAIL;
 351                                 break;
 352                         case JTAG_SCAN:
 353                                 bitbang_end_state(cmd->cmd.scan->end_state);
 354                                 scan_size = jtag_build_buffer(cmd->cmd.scan, &buffer);
 355                                 LOG_DEBUG_IO("%s scan %d bits; end in %s",
 356                                                 (cmd->cmd.scan->ir_scan) ? "IR" : "DR",
 357                                                 scan_size,
 358                                         tap_state_name(cmd->cmd.scan->end_state));
 359                                 type = jtag_scan_type(cmd->cmd.scan);
 360                                 if (bitbang_scan(cmd->cmd.scan->ir_scan, type, buffer,
 361                                                         scan_size) != ERROR_OK)
 362                                         return ERROR_FAIL;
 363                                 if (jtag_read_buffer(buffer, cmd->cmd.scan) != ERROR_OK)
 364                                         retval = ERROR_JTAG_QUEUE_FAILED;
 365                                 free(buffer);
 366                                 break;
 367                         case JTAG_SLEEP:
 368                                 LOG_DEBUG_IO("sleep %" PRIu32, cmd->cmd.sleep->us);
 369                                 if (bitbang_interface->flush && (bitbang_interface->flush() != ERROR_OK))
 370                                         return ERROR_FAIL;
 371                                 bitbang_sleep(cmd->cmd.sleep->us);
 372                                 break;
 373                         case JTAG_TMS:
 374                                 retval = bitbang_execute_tms(cmd);
 375                                 break;
 376                         default:
 377                                 LOG_ERROR("BUG: unknown JTAG command type encountered");
 378                                 exit(-1);
 379                 }
 380                 cmd = cmd->next;
 381         }
 382         if (bitbang_interface->blink) {
 383                 if (bitbang_interface->blink(0) != ERROR_OK)
 384                         return ERROR_FAIL;
 385         }
 386
 387         return retval;
 388 }
 389
 390 static int queued_retval;
 391
 392 static int bitbang_swd_init(void)
 393 {
 394         LOG_DEBUG("bitbang_swd_init");
 395         return ERROR_OK;
 396 }
 397
 398 static void bitbang_swd_exchange(bool rnw, uint8_t buf[], unsigned int offset, unsigned int bit_cnt)
 399 {
 400         if (bitbang_interface->blink) {
 401                 /* FIXME: we should manage errors */
 402                 bitbang_interface->blink(1);
 403         }
 404
 405         for (unsigned int i = offset; i < bit_cnt + offset; i++) {
 406                 int bytec = i/8;
 407                 int bcval = 1 << (i % 8);
 408                 int swdio = !rnw && (buf[bytec] & bcval);
 409
 410                 bitbang_interface->swd_write(0, swdio);
 411
 412                 if (rnw && buf) {
 413                         if (bitbang_interface->swdio_read())
 414                                 buf[bytec] |= bcval;
 415                         else
 416                                 buf[bytec] &= ~bcval;
 417                 }
 418
 419                 bitbang_interface->swd_write(1, swdio);
 420         }
 421
 422         if (bitbang_interface->blink) {
 423                 /* FIXME: we should manage errors */
 424                 bitbang_interface->blink(0);
 425         }
 426 }
 427
 428 static int bitbang_swd_switch_seq(enum swd_special_seq seq)
 429 {
 430         switch (seq) {
 431         case LINE_RESET:
 432                 LOG_DEBUG_IO("SWD line reset");
 433                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_line_reset, 0, swd_seq_line_reset_len);
 434                 break;
 435         case JTAG_TO_SWD:
 436                 LOG_DEBUG("JTAG-to-SWD");
 437                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_jtag_to_swd, 0, swd_seq_jtag_to_swd_len);
 438                 break;
 439         case JTAG_TO_DORMANT:
 440                 LOG_DEBUG("JTAG-to-DORMANT");
 441                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_jtag_to_dormant, 0, swd_seq_jtag_to_dormant_len);
 442                 break;
 443         case SWD_TO_JTAG:
 444                 LOG_DEBUG("SWD-to-JTAG");
 445                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_swd_to_jtag, 0, swd_seq_swd_to_jtag_len);
 446                 break;
 447         case SWD_TO_DORMANT:
 448                 LOG_DEBUG("SWD-to-DORMANT");
 449                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_swd_to_dormant, 0, swd_seq_swd_to_dormant_len);
 450                 break;
 451         case DORMANT_TO_SWD:
 452                 LOG_DEBUG("DORMANT-to-SWD");
 453                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_dormant_to_swd, 0, swd_seq_dormant_to_swd_len);
 454                 break;
 455         case DORMANT_TO_JTAG:
 456                 LOG_DEBUG("DORMANT-to-JTAG");
 457                 bitbang_swd_exchange(false, (uint8_t *)swd_seq_dormant_to_jtag, 0, swd_seq_dormant_to_jtag_len);
 458                 break;
 459         default:
 460                 LOG_ERROR("Sequence %d not supported", seq);
 461                 return ERROR_FAIL;
 462         }
 463
 464         return ERROR_OK;
 465 }
 466
 467 static void swd_clear_sticky_errors(void)
 468 {
 469         bitbang_swd_write_reg(swd_cmd(false,  false, DP_ABORT),
 470                 STKCMPCLR | STKERRCLR | WDERRCLR | ORUNERRCLR, 0);
 471 }
 472
 473 static void bitbang_swd_read_reg(uint8_t cmd, uint32_t *value, uint32_t ap_delay_clk)
 474 {
 475         assert(cmd & SWD_CMD_RNW);
 476
 477         if (queued_retval != ERROR_OK) {
 478                 LOG_DEBUG("Skip bitbang_swd_read_reg because queued_retval=%d", queued_retval);
 479                 return;
 480         }
 481
 482         int64_t timeout = timeval_ms() + SWD_WAIT_TIMEOUT;
 483         for (unsigned int retry = 0;; retry++) {
 484                 uint8_t trn_ack_data_parity_trn[DIV_ROUND_UP(4 + 3 + 32 + 1 + 4, 8)];
 485
 486                 cmd |= SWD_CMD_START | SWD_CMD_PARK;
 487                 bitbang_swd_exchange(false, &cmd, 0, 8);
 488
 489                 bitbang_interface->swdio_drive(false);
 490                 bitbang_swd_exchange(true, trn_ack_data_parity_trn, 0, 1 + 3 + 32 + 1 + 1);
 491                 bitbang_interface->swdio_drive(true);
 492
 493                 int ack = buf_get_u32(trn_ack_data_parity_trn, 1, 3);
 494                 uint32_t data = buf_get_u32(trn_ack_data_parity_trn, 1 + 3, 32);
 495                 int parity = buf_get_u32(trn_ack_data_parity_trn, 1 + 3 + 32, 1);
 496
 497                 LOG_CUSTOM_LEVEL((ack != SWD_ACK_OK && (retry == 0 || ack != SWD_ACK_WAIT))
 498                                 ? LOG_LVL_DEBUG : LOG_LVL_DEBUG_IO,
 499                         "%s %s read reg %X = %08" PRIx32,
 500                         ack == SWD_ACK_OK ? "OK" : ack == SWD_ACK_WAIT ? "WAIT" : ack == SWD_ACK_FAULT ? "FAULT" : "JUNK",
 501                         cmd & SWD_CMD_APNDP ? "AP" : "DP",
 502                         (cmd & SWD_CMD_A32) >> 1,
 503                         data);
 504
 505                 if (ack == SWD_ACK_WAIT && timeval_ms() <= timeout) {
 506                         swd_clear_sticky_errors();
 507                         if (retry > 20)
 508                                 alive_sleep(1);
 509
 510                         continue;
 511                 }
 512                 if (retry > 1)
 513                         LOG_DEBUG("SWD WAIT: retried %u times", retry);
 514
 515                 if (ack != SWD_ACK_OK) {
 516                         queued_retval = swd_ack_to_error_code(ack);
 517                         return;
 518                 }
 519
 520                 if (parity != parity_u32(data)) {
 521                         LOG_ERROR("Wrong parity detected");
 522                         queued_retval = ERROR_FAIL;
 523                         return;
 524                 }
 525                 if (value)
 526                         *value = data;
 527                 if (cmd & SWD_CMD_APNDP)
 528                         bitbang_swd_exchange(true, NULL, 0, ap_delay_clk);
 529                 return;
 530         }
 531 }
 532
 533 static void bitbang_swd_write_reg(uint8_t cmd, uint32_t value, uint32_t ap_delay_clk)
 534 {
 535         assert(!(cmd & SWD_CMD_RNW));
 536
 537         if (queued_retval != ERROR_OK) {
 538                 LOG_DEBUG("Skip bitbang_swd_write_reg because queued_retval=%d", queued_retval);
 539                 return;
 540         }
 541
 542         int64_t timeout = timeval_ms() + SWD_WAIT_TIMEOUT;
 543
 544         /* Devices do not reply to DP_TARGETSEL write cmd, ignore received ack */
 545         bool check_ack = swd_cmd_returns_ack(cmd);
 546
 547         /* init the array to silence scan-build */
 548         uint8_t trn_ack_data_parity_trn[DIV_ROUND_UP(4 + 3 + 32 + 1 + 4, 8)] = {0};
 549         for (unsigned int retry = 0;; retry++) {
 550                 buf_set_u32(trn_ack_data_parity_trn, 1 + 3 + 1, 32, value);
 551                 buf_set_u32(trn_ack_data_parity_trn, 1 + 3 + 1 + 32, 1, parity_u32(value));
 552
 553                 cmd |= SWD_CMD_START | SWD_CMD_PARK;
 554                 bitbang_swd_exchange(false, &cmd, 0, 8);
 555
 556                 bitbang_interface->swdio_drive(false);
 557                 bitbang_swd_exchange(true, trn_ack_data_parity_trn, 0, 1 + 3);
 558
 559                 /* Avoid a glitch on SWDIO when changing the direction to output.
 560                  * To keep performance penalty minimal, pre-write the first data
 561                  * bit to SWDIO GPIO output buffer while clocking the turnaround bit.
 562                  * Following swdio_drive(true) outputs the pre-written value
 563                  * and the same value is rewritten by the next swd_write()
 564                  * instead of glitching SWDIO
 565                  * HiZ/pull-up --------------> 0 -------------> 1
 566                  *           swdio_drive(true)   swd_write(0,1)
 567                  * in case of data bit 0 = 1
 568                  */
 569                 bitbang_swd_exchange(false, trn_ack_data_parity_trn, 1 + 3 + 1, 1);
 570                 bitbang_interface->swdio_drive(true);
 571                 bitbang_swd_exchange(false, trn_ack_data_parity_trn, 1 + 3 + 1, 32 + 1);
 572
 573                 int ack = buf_get_u32(trn_ack_data_parity_trn, 1, 3);
 574                 LOG_CUSTOM_LEVEL((check_ack && ack != SWD_ACK_OK && (retry == 0 || ack != SWD_ACK_WAIT))
 575                                 ? LOG_LVL_DEBUG : LOG_LVL_DEBUG_IO,
 576                         "%s%s %s write reg %X = %08" PRIx32,
 577                         check_ack ? "" : "ack ignored ",
 578                         ack == SWD_ACK_OK ? "OK" : ack == SWD_ACK_WAIT ? "WAIT" : ack == SWD_ACK_FAULT ? "FAULT" : "JUNK",
 579                         cmd & SWD_CMD_APNDP ? "AP" : "DP",
 580                         (cmd & SWD_CMD_A32) >> 1,
 581                         buf_get_u32(trn_ack_data_parity_trn, 1 + 3 + 1, 32));
 582
 583                 if (check_ack && ack == SWD_ACK_WAIT && timeval_ms() <= timeout) {
 584                         swd_clear_sticky_errors();
 585                         if (retry > 20)
 586                                 alive_sleep(1);
 587
 588                         continue;
 589                 }
 590
 591                 if (retry > 1)
 592                         LOG_DEBUG("SWD WAIT: retried %u times", retry);
 593
 594                 if (check_ack && ack != SWD_ACK_OK) {
 595                         queued_retval = swd_ack_to_error_code(ack);
 596                         return;
 597                 }
 598
 599                 if (cmd & SWD_CMD_APNDP)
 600                         bitbang_swd_exchange(true, NULL, 0, ap_delay_clk);
 601                 return;
 602         }
 603 }
 604
 605 static int bitbang_swd_run_queue(void)
 606 {
 607         /* A transaction must be followed by another transaction or at least 8 idle cycles to
 608          * ensure that data is clocked through the AP. */
 609         bitbang_swd_exchange(true, NULL, 0, 8);
 610
 611         int retval = queued_retval;
 612         queued_retval = ERROR_OK;
 613         LOG_DEBUG_IO("SWD queue return value: %02x", retval);
 614         return retval;
 615 }
 616
 617 const struct swd_driver bitbang_swd = {
 618         .init = bitbang_swd_init,
 619         .switch_seq = bitbang_swd_switch_seq,
 620         .read_reg = bitbang_swd_read_reg,
 621         .write_reg = bitbang_swd_write_reg,
 622         .run = bitbang_swd_run_queue,
 623 };