JTAG is mainly used for debugging, mainly for internal chip testing

The following is from Baidu:

Often referred to as JTAG roughly divided into two categories, one used to test the electrical characteristics of the chip to detect the chip whether there is a problem; a class of Debug, the general support for JTAG CPU contains these two modules.

A CPU containing a JTAG Debug interface module, as long as the clock is normal, you can use the JTAG interface to access the CPU's internal registers and devices hanging on the CPU bus, such as FLASH, RAM, SOC (such as the 4510B, 44Box, AT91M series) built-in modules, such as the registers UART, Timers, GPIOs and so on. GPIOs, etc.

The above is only the ability of the JTAG interface, to use these functions, but also need to cooperate with the software, the specific realization of the function is determined by the specific software.

JTAG (Joint Test Action Group) is an international standard test protocol, mainly used for internal chip testing and system simulation, debugging, JTAG technology is an embedded debugging technology, which is encapsulated inside the chip with a specialized test circuit TAP (Test Access Port). Access Port), through a dedicated JTAG test tool to test the internal nodes.