+ int retval;
+ uint32_t dpidr = 0xdeadbeef;
+ uint32_t dlpidr = 0xdeadbeef;
+ int64_t timeout = timeval_ms() + 500;
+
+ do {
+ swd_send_sequence(dap, JTAG_TO_DORMANT);
+ swd_send_sequence(dap, DORMANT_TO_SWD);
+
+ /* Clear link state, including the SELECT cache. */
+ dap->do_reconnect = false;
+ dap_invalidate_cache(dap);
+ swd_multidrop_selected_dap = NULL;
+
+ retval = swd_multidrop_select_inner(dap, &dpidr, &dlpidr, true);
+ if (retval == ERROR_OK)
+ break;
+
+ alive_sleep(1);
+
+ } while (timeval_ms() < timeout);
+
+ if (retval != ERROR_OK) {
+ swd_multidrop_selected_dap = NULL;
+ LOG_ERROR("Failed to connect multidrop %s", adiv5_dap_name(dap));
+ return retval;
+ }
+
+ LOG_INFO("SWD DPIDR 0x%08" PRIx32 ", DLPIDR 0x%08" PRIx32,
+ dpidr, dlpidr);
+
+ return retval;
+}
+
+static int swd_connect_single(struct adiv5_dap *dap)
+{
+ int retval;
+ uint32_t dpidr = 0xdeadbeef;
+ int64_t timeout = timeval_ms() + 500;
+
+ do {
+ if (dap->switch_through_dormant) {
+ swd_send_sequence(dap, JTAG_TO_DORMANT);
+ swd_send_sequence(dap, DORMANT_TO_SWD);
+ } else {
+ swd_send_sequence(dap, JTAG_TO_SWD);
+ }
+
+ /* Clear link state, including the SELECT cache. */
+ dap->do_reconnect = false;
+ dap_invalidate_cache(dap);
+
+ /* The sequences to enter in SWD (JTAG_TO_SWD and DORMANT_TO_SWD) end
+ * with a SWD line reset sequence (50 clk with SWDIO high).
+ * From ARM IHI 0074C ADIv6.0, chapter B4.3.3 "Connection and line reset
+ * sequence":
+ * - line reset sets DP_SELECT_DPBANK to zero;
+ * - read of DP_DPIDR takes the connection out of reset;
+ * - write of DP_TARGETSEL keeps the connection in reset;
+ * - other accesses return protocol error (SWDIO not driven by target).
+ *
+ * Read DP_DPIDR to get out of reset. Initialize dap->select to zero to
+ * skip the write to DP_SELECT, avoiding the protocol error. Set again
+ * dap->select to DP_SELECT_INVALID because the rest of the register is
+ * unknown after line reset.
+ */
+ dap->select = 0;
+ retval = swd_queue_dp_read_inner(dap, DP_DPIDR, &dpidr);
+ if (retval == ERROR_OK) {
+ retval = swd_run_inner(dap);
+ if (retval == ERROR_OK)
+ break;
+ }
+
+ alive_sleep(1);
+
+ dap->switch_through_dormant = !dap->switch_through_dormant;
+ } while (timeval_ms() < timeout);
+
+ dap->select = DP_SELECT_INVALID;
+
+ if (retval != ERROR_OK) {
+ LOG_ERROR("Error connecting DP: cannot read IDR");
+ return retval;
+ }
+
+ LOG_INFO("SWD DPIDR 0x%08" PRIx32, dpidr);
+
+ do {
+ dap->do_reconnect = false;
+
+ /* force clear all sticky faults */
+ swd_clear_sticky_errors(dap);
+
+ retval = swd_run_inner(dap);
+ if (retval != ERROR_WAIT)
+ break;
+
+ alive_sleep(10);
+
+ } while (timeval_ms() < timeout);
+
+ return retval;
+}
+
+static int swd_connect(struct adiv5_dap *dap)
+{
+ int status;
+
+ /* FIXME validate transport config ... is the
+ * configured DAP present (check IDCODE)?
+ */
+
+ /* Check if we should reset srst already when connecting, but not if reconnecting. */
+ if (!dap->do_reconnect) {
+ enum reset_types jtag_reset_config = jtag_get_reset_config();
+
+ if (jtag_reset_config & RESET_CNCT_UNDER_SRST) {
+ if (jtag_reset_config & RESET_SRST_NO_GATING)
+ adapter_assert_reset();
+ else
+ LOG_WARNING("\'srst_nogate\' reset_config option is required");
+ }
+ }
+
+ if (dap_is_multidrop(dap))
+ status = swd_connect_multidrop(dap);
+ else
+ status = swd_connect_single(dap);
+
+ /* IHI 0031E B4.3.2:
+ * "A WAIT response must not be issued to the ...
+ * ... writes to the ABORT register"
+ * swd_clear_sticky_errors() writes to the ABORT register only.
+ *
+ * Unfortunately at least Microchip SAMD51/E53/E54 returns WAIT
+ * in a corner case. Just try if ABORT resolves the problem.
+ */
+ if (status == ERROR_WAIT) {
+ LOG_WARNING("Connecting DP: stalled AP operation, issuing ABORT");
+
+ dap->do_reconnect = false;
+
+ status = swd_queue_dp_write_inner(dap, DP_ABORT,
+ DAPABORT | STKCMPCLR | STKERRCLR | WDERRCLR | ORUNERRCLR);
+
+ if (status == ERROR_OK)
+ status = swd_run_inner(dap);
+ }
+
+ if (status == ERROR_OK)
+ status = dap_dp_init(dap);
+
+ return status;