Protocol

JTAG

IEEE 1149.1

Boundary-scan and debug TAP with TMS/TCK/TDI/TDO state machine. Chains, IR/DR lengths, and adaptive clocking matter when probing multi-chip boards.

Domains

ARM two-pin debug protocol (SWDIO/SWCLK) replacing full JTAG for Cortex-M. Packets select DP/AP registers for memory access, breakpoints,…

ARM Cortex single-pin async trace for printf-style ITM packets and event counters. Baud must match debugger; Manchester vs UART encoding …