Sun Keyboard to USB converter

Introduction

This firmware defines a USB keyboard which uses a Sun Type 5/6 keyboard as input. The firmware works in conjunction with a PJRC Teensy 2.0 together with some modifications for handling the transport of packets to/from the keyboard, button debouncing, status leds and jumper based configuration.

TL;DR

1. Configure the jumpers to enable bootloader support
2. Attach keyboard to controller
3. Attach controller to USB cable
4. Run the following commands:

make clean
make all
make program

Hardware overview

The Sun Type 5/6 keyboard communicates over 1200 baud ttl-232 serial, using inverted logic levels, which need to be inverted in order to use them. Apart from that, connecting this keyboard to a modern pc is a matter of reading, converting and transmitting the scancodes, which keeps the amount of modifications to a minimum.

![Schematic of controller][id] [id]: https://raw.github.com/r3boot/sunkbd/master/eagle/sunkbd_schematic.png "Controller schematic"

The keyboards RX/TX lines are connected through a hex inverter based on a 7404N, before being put onto the D2/D3 ports of the onboard UART. A common-anode dual-color led is used to inform the user of RX/TX traffic, or to signal an error. This led is connected using R2,R3 to the F0/F1 ports on the teensy. A switch together with a capacitor based debouncing circuit (R1, C1) are fed into a NAND Schmitt Trigger based on a 7414 to further smooth out the signal, which is then transported to the B0 pin of the teensy. Finally, a set of jumpers which can be bound to ground are connected to pins D1,D2,D3, to provide a way of configuring the firmware in the field. Pins D0..D3 use internal pull-up resistors.

Software overview

The software consists of a couple of drivers for both the onboard UART as well as the onboard USB chip, bound together using scancode conversion logic and buffers for the UART and the USB keyboard.

There are various states in which the keyboard operates. At first startup, when the keyboard isn't initialized, the firmware will send a reset code to the keyboard. Depending on the result returned by the keyboard, the keyboard is either initialized, or it will fail, but will keep sending scancodes.

When the keyboard is initialized, and a scancode is received, the firmware will first determine what kind of scancode is received. Based on this, it will set modifier and/or led status. If the key is a pc105 scancode, the key will be added/removed from the keyboard buffer, whenever the key is pressed/released. Whenever a multimedia key has been detected, it will be sent over a remote control USB hid descriptor, allowing the host computer to use the keys as multimedia keys.

Jumper based configuration

To allow configuration in the field, a set of jumpers has been created which can be used to configure various settings which are defined during startup of the firmware. The current implementation uses bit-masks for configuration settings, allowing a maximum of 3 field-configurable options. A possible future modification might make this an integer-based configuration allowing more configuration options. Below you can find a list of jumper/pin mappings and their functions

PIN     JUMPER  DESCRIPTION
PB1     J0      Enable keyboard clicks. When this jumper is bridged, a sound
                will be created by the keyboard, giving a audible feedback.
PB2     J1      Enable debug support. Bridging this jumper will enable the
                USB raw-hid debugging channel. Only useful during development
PB3     J2      Enable bootloader support. By bridging this jumper, the MCU
                will jump to the HalfKay bootloader instead of resetting when
                the reset button is pressed.