During these early phases, the bootloader often gives information over the serial port and can respond to its own set of commands. Typically, a router first starts its “permanent” bootloader which is responsible for the first steps of finding the OpenWrt firmware and starting OpenWrt running.

Most routers come with an UART integrated into the System-on-chip and its pins are routed on the Printed Circuit Board (PCB) to allow debugging, firmware replacement or serial device connection (like modems). If one wishes a more permanent installation, mechanical skills in modifying the case may also be needed. The cost of components is relatively low a 10-euro/dollar project if one uses “eBay-grade” parts (which are likely sufficient). Console access to the bootloader will often allow one to fetch and flash new firmware and may be the only way to do so on some routers if the firmware is not functional.Įnabling a serial port, if there is not one already available on the case, typically involves opening the case and basic soldering skills. A console to the running system will let you correct a misconfigured network, for example. These serial ports typically provide a console to the bootloader and, when the firmware has booted, a console to the running system.

Most devices supported by OpenWrt have or can be modified to have a serial port. However, some bootloaders don't have a “really failsafe” network re-flash feature, making a serial console one of the few ways to recover from a “bad flash” or an error in a user's own configuration. Most people get along without a serial console for their device because they're able to flash a working firmware the first time - or are able to apply various recovery methods - and do all their communicating with the device over a network.

Multimeter test serial connection