24th of April 2021 Porting GS BASIC – to PiTrex (4)

Today I coded nearly “nothing”. First I had to do much around the house. Second – I researched the Vecterx32 BASIC a little closer:

Since I never programmed a PIC and I do not have much experience (none) with RTOS – and I only glimps at code pieces I need “now”… I can sometimes only guess, what is keeping things together.

I was wondering how the different “pieces” of software go together… and I think I found it deep in one of the directories I never needed to look at… there is a directory called:

/dev/Vectrex/SmartCart/SmartCart/firmware/src/system_config/PIC32MZ2048EFH064

and within that directory is what I guess the “system setup”. The PIC seems to be running an OS called RTOS, the operating systems has a task scheduler and is started with 4 tasks:

• system task
• console task
• vectrex task
• app task

Without going into any code, my guess is:

System task is for the OS “housekeeping” (USB accesses, File systems…), console task for basic i/o / terminal and user input output, app task runs the actual user program (in this case the BASIC) and here a special “vectrex task”, which handles talking to vectrex, putting commandlists into the Dual RAM and synchronize things.

The “splitup” into different tasks running more or less independendly got me a little bit mixed up. I have been programming pure vectrex and piTrex baremetal for too long – I had nearly forgotten about message passing, callbacks and different tasks (processes)…. and I wondered, why I could never find a section within the BASIC, that does the actual i/o :-).

I also realized, that I have to implement something into my own VectrexInterface which I have been “talking” about – but not yet realized: “persistent vectors”

Implementing those will greately ease any further Vectrex32 BASIC porting. Take a look at this little BASIC sample:

call IntensitySprite(72)

textSize = {40, 5}
call TextSizeSprite(textSize)
instructions = {{-50, 90, "INSTRUCTIONS"}, _
                {-80, 70, "JOYSTK IS THRUST"}, _
                {-80, 50, "BTNS 1&2 ROTATE"}, _
                {-80, 30, "BTN 4 EXITS"}, _
                {-80, 1, "PRESS BTN 1 TO START"}}

call TextListSprite(instructions)

' Wait for button 1 or button 4
controls = WaitForFrame(JoystickNone, Controller1, JoystickNone)
while controls[1, 3] = 0 and controls[1, 6] = 0
     controls = WaitForFrame(JoystickNone, Controller1, JoystickNone)
endwhile

What the orange code actually is – it is a vectrex frame loop. In the common vectrex sense it displays nothing, but just waits for a joystick input.

In the Vectrex32 sense – all text output is initialized beforehand as persistent “output” elements, which get redisplayed, till the screen is cleared or single elements are removed.

As of now, the vectrexInterface does not per default support such constructs. But I have been talking about supporting this for quite some time now… So… this is what I’ll do next.

Add “persistent vectors” to the vectrexInterface and THAN return to the Vectrex32 BASIC.
No worries, that (if I find the time at all) will not take long. Since even now the complete output is done using a “pipeline” which contains (in Vectrex32 BASIC speaking:) compiled elements – I just have to flag them as persistent and than to not delete “flagged” elements.

If I do not have to much houskeeping activities on my plate tomorrow, we might see that “instruction” loop displayed on a vectrex :-).

Cheers