I recall a TEST/LOOPBACK circuit in 8088 (port 0x0A). It was discussed in


- but it is not implemented in our present source (Git).

Bit 5 redirects one output to another input during inital tests, and is unique to the Rainbow.

In my understanding, serial, printer and keyboard are tested in one large loop, so that interfaces must be fully functional (and redirectable by bit 5). As things stand now, this is not the case (else errors 40 and 60 for serial/printer would be absent at boot time).

Another indication: 8088 registers 0x02, 0x06, 0x0e are not implemented in 'rainbow.cpp' (unless i missed a super secret fork).

@R.Belmont: please forgive my stubbornness smile

[Linked Image from dl.dropboxusercontent.com]

(CLICK TO ENLARGE IMAGE; circuit in upper left corner)

Last edited by Bavarese; 06/03/16 03:46 PM.