31.5 POST codes

If a UEFI driver is being developed that cannot make use of the DEBUG() and ASSERT() macros, then a different mechanism must be used to help in the debugging process. Under these conditions, it is usually sufficient to send a small amount of output to a device to indicate what portions of a UEFI driver have executed and where error conditions have been detected.
A few possibilities are presented in this discussion, but many others are possible depending on the devices that may be available on a specific platform. The first possibility is to use a POST card. Another is to use a text-mode VGA frame buffer.
It is important to note that mechanisms are useful during driver development and debug, but they should never be present in production versions of UEFI drivers because these types of devices are not present on all platforms and accessing these devices may cause unexpected behavior on platforms that do not include those devices.