Category: I/O
Tool: Diamond
Device: MachXO2, MachXO3

The JTAGENB pin controls whether the JTAG related pins (TMS/TCK/TDI/TDO) are used exclusively for JTAG or as general purpose I/O. In the "Global Preferences" tab of Diamond's "Spreadsheet View", if you set JTAG_PORT="ENABLE" (Default), the JTAGENB pin will be a general purpose IO and TMS/TCK/TDI/TDO will be JTAG dedicated pins. On the other hand, if JTAG_PORT="DISABLE" is set, the JTAGENB pin becomes a dedicated input pin, and depending on its voltage level, the JTAG related pins behave as follows.

<When JTAGENB=High>
TMS/TCK/TDI/TDO: All JTAG dedicated pins
<When JTAGENB=Low>
TMS/TCK/TDI/TDO: all user I/O

Basically, set JTAG_PORT="ENABLE", and set JTAG_PORT="DISABLE" only when the number of I/Os is unavoidably insufficient. Even in such a case, when designing the board, be sure to provide a means to pull the JTAGENB pin high as a emergency measure.
Also, when JTAG_PORT="ENABLE", the JTAGENB pin becomes a general-purpose I/O, so it can be left open if not used.