Psion Organiser II datapak replacement using RP2040
Code for a replacement Psion datapak that uses the RP2040 to create a datapak image that is interfaced using one of the datapak slots in the Organiser. The gadget has an SD slot that can hold .opk files which are presented to the organiser as a datapak. There's a small OLED display and buttons so the image can be selected. The pak gadget can also present a rampak and data can be stored on the ram pak. That can then be saved to SD card using the menu system. Power is USB as the datapak interface does not have a permanent power supply.
There are two versions:
A 'breakout' pak-gadget which is a T shaped PCB that plugs in to the datapak slot and has the display and buttons facing forwards. This is quite large.
This is a pak-gadget that fits in the form factor of a datapak in the slot in the organiser. It has a smaller OLED display and buttons that both face towards the back of the organiser. Power is still USB. When disconnected from power the organiser cover should fit in the closed position. The gadget can be wired in to the internal power supply of the organiser.On older PCB designs this requires an external transistor and a wire to the gadget. The later designs have that on the gadget PCB and require two wires.
The pak gadget plugs in to either datapack slot on a Psion Organiser 2. It can be powered by the USB socket on the PCB, or it can be wired in to the internal supply of the organiser. A transistor is needed to switch the battery voltage on to the gadget when the LCD controller is turned on. When wired in the USB connection MUST NOT be used. A later revision of the PCB (untested as yet) has the extra transistor needed for internal power on the PCB.
The gadget runs in a tight loop when emulating a datapack in order to operate at the speeds needed to interact with the Psion, which means it cannot handle a menu while emulating.
There are four buttons on the gadget. The left most button breaks the gadget out of its tight loop and starts a menu. UP and DOWN are the rightmost two buttons. The button second from left is an OK button.
The code reads a file called config.txt from the SD card when it starts up. At the moment this just sets the .OPK image that will initially be used. pack header bytes are passed through from the OPk file to the organiser unchanged, apart from the size byte. The pak gadget can only support pack images up to and including 128K so the size byte is altered to be no larger than 128K.
This lists the .OPK files on the SD card. Selecting a file loads it into the gadget RAM buffer ready to emulate it when the menu is exited.
This writes the current RAM data to a file on the SD card. This enables a pak gadget that has been used as a RAM pack to save the data on SD card so that it can be loaded back in later. When power is removed the RAM b uffer is lost so this is the only way to have non volatile storage with the pak gadget.
The files are written with the name: paknnnnn.opk
where nnnnn is an increasing number for each file saved. The pak gadget checks for the last nnnnn used by a file on the SD card and picks the next highest number for each file write.
This clears the RAM buffer and sets the pak gadget up as a blank pack which can then be sized and used as a RAM pack.
This exits the menu and enters the emulation loop so that the pak gadget will look like a datapack again. While in the menu system the gadget does not emulate a pack.