assert(dap_is_multidrop(dap));
swd_send_sequence(dap, LINE_RESET);
+ /* 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_write_inner(dap, DP_TARGETSEL, dap->multidrop_targetsel);
if (retval != ERROR_OK)
return retval;
}
+ dap->select = DP_SELECT_INVALID;
+
retval = swd_queue_dp_read_inner(dap, DP_DLPIDR, &dlpidr);
if (retval != ERROR_OK)
return retval;
dap->switch_through_dormant = !dap->switch_through_dormant;
} while (timeval_ms() < timeout);
+
dap->select = DP_SELECT_INVALID;
if (retval != ERROR_OK) {