HP-71b - Future "SD-RAM" Module - viable ?

[J-F Garnier]

(09-07-2022 02:14 PM)mfleming Wrote:  

(09-07-2022 07:15 AM)J-F Garnier Wrote:  An other possible approach would be to manage the SD card as a new device type for instance XMEM (like the 75C POD) or EDISC. The HP-71B system is designed in such a way that the HP-71B will poll the LEX files for a handler for unknown device types (this is how the HP-IL ROM extends the built-in command CAT, COPY , ...). So all you would have to do is to write a LEX file to manage your SD card, in the way you want.

So, if I understand you correctly, you start with creating a new device and hook its LEX handlers into existing commands (CAT, COPY, ...) and add new commands to reflect the device storage model. Commands like CD, PWD, MKDIR for a FAT-based storage model or MOUNT, UMOUNT if you want to keep a LIF disk model of storage. If hardware is implemented in the card reader slot the LEX code would manage hardware via the card reader device address.

Yes. When you will do COPY file:XMEM , the HP-71B will poll all LEXs asking for one able to manage the XMEM device. Then the LEX code (the HP-71B code you will have to create) will get control and will have to do everything: find the file in the SD card or from the BT (not so difficult), allocate the HP-71B memory to receive the file (already a bit harder), create the catalog entry and the timestamp, link the file in the HP-71B file chain for the catalog, set the relevant and obscure file copy codes and probably other things like managing all errors, triggering a HP-71B system reconfiguration in case a LEX file is copied, ...
A big job, actually almost a no-go. Sorry my "So all you would have to" was a bit provocative.

So on second thought, it may be easier to emulate a second HP-IL interface (the so called "HP-IL mailbox"). I'm sure you can do it based on of the Multimod technology.
The HP-IL ROM code will manage everything on the HP-71B side (no extra HP-71B code will be required), it will just be your responsibility to present a HP-IL mass storage to this interface, very similar to Tobie's IL drive.
Both the HP-IL mailbox protocol and the HP-IL mass storage command set are well documented, and already implemented in Emu71. So it seems much more doable.

The drawback is that you will be limited to the flat LIF-type disc images and HP-71B file types. No MKDIR, CD, etc...
The best you can do is to present several mass storage units (up to 30), knowing that the HP-71B (actually the mass storage protocol) can manage volumes up to 16MB.
But 30 x 16MB = 480 MB is more than enough!
The usage will be for instance: "COPY file:SD5:2" that would mean: copy myfile from the 5th mass storage unit on the 2nd loop (your emulated loop).

(09-08-2022 10:13 PM)vassilisprevelakis Wrote:  Unfortunately emulating an HP-IL peripheral controller may not be possible as the card reader interface is missing the !INT and OD signals (which exist on the HP-IL connector).

The OD (used to disable system ROMs) is not needed for sure, and I'm almost sure the *INT is not used by the HP-IL. The HP-IL uses the software Service Request (SRQ) mechanism to get attention from the HP-71B. Don't be mislead by the term "interrupt" in the 71 HP-IL IDS.
However, I will double check this point.

J-F