The highest level is the public function interface, which operate in terms of entities that are visible in GDB: open and close the connection, read and write SPRs, read and write memory, stall, unstall and wait for the processor. These functions always succeed and have function prefixes or1k_jtag_.

The next level is the abstraction provided by the OR1K JTAG protocol: read/write a JTAG register, read/write a block of JTAG registers and select a scan chain. These functions may encounter errors and will deal with them, but otherwise return no error result. These are static functions (i.e. local to this file), with prefixes or1k_jtag_.

The next level is in two sets, one for use with a locally connected (JP1) JTAG and one for a remote connection over TCP/IP corresponding to the functions in the previous layer. These functions detect with errors and return an error code to indicate an error has occurred. These are static functions with prefixes: jp1_ and jtr_ respectively.

The final level comes in separate flavors for locally connected JTAG (low level routines to drive the JP1 interface) and remote use (to build and send/receive packets over TCP/IP). These functions detect errors and return an error code to indicate an error has occurred. These are static function with prefixes jp1_ll_ and jtr_ll_ respectively.