Extending C128 BASIC using REM statement parameters

 

So on the C64 you could have commands like SYS 49152,X,Y,"TEXT" where your machine/assembly code could specifically parse the commas and numbers.  The result was a way to interface between BASIC and Assembly to use the best of both worlds.   BASIC is easy to edit, debug, and change.  6502 is fast and can do some low level operations including accessing all 64K RAM, and all the ROMs.

BUT!!!   On the C128, the SYS command was extended to allow ease of passing registers.  This is fine if you want to transfer data in 0..255 chunks.  But coordinates on the screen are 320x200, so that goes past a byte, and addresses are 0..65535, they definitely go past a byte.  And strings are another animal.

On the C128 the statement SYS 4864,1,2,3 will call the routine with .A, .X, .Y registers populated with 1, 2, and 3 respectively.  That's fine and dandy, but if you want to do something more, you have to do it another way.

Here comes the new syntax:

SYS 4864 : REM 300, 65535, "Hello C128"

By using the token getter, you can check for colon, REM token, then proceed to parse values and variables as before on C64.  (With the exception that I couldn't get expressions like 2+3 to work, maybe something to do with REM.  But we can work around that.)

Check out the github repository for program listings including commented assembly for more details, and to grab a copy of the D64 containing the PRG.

Touch points and buttons on M5Core 2" displays, Tab 5" display, and Sunton 7" display for keyboard emulation

I have targeted the following M5 Stack models with my C64/C128/Vic-20/Apple 1 emulator:

• M5Stack Fire IoT
• M5 Core2
• M5 CoreS3

(Even though I have targeted other boards, I had only implemented touch on the CoreS3)

The primary reason for targeting these boards was the common 2" 320x240 display perfect for most C64 emulation, and the availability of a wristband that works with Core2 and CoreS3 (it works with the Fire if and only if you never need to charge the battery - not aware of a universe where that works out long term).

[aside... Originally I had supported the M5 Core Basic, but without PSRAM, it was difficult to support the different computer models that currently load into that memory.  So M5 Core BASIC was dropped after its initial development.]

The Basic and Fire have three UI hardware buttons.   The Core2 has three virtual touchscreen buttons (touchscreen expands farther down from the LCD screen to allow for capacitive touch button points, and the M5 library abstracts them similar to physical buttons, so your code doesn't even have to know the difference).  The CoreS3 has no UI buttons, but I've manually implemented virtual touch screen buttons at the bottom of the screen.   From left to right the buttons are known to M5 as A, B, and C.

So button support for Basic, Fire, and Core2 was straightforward.

• press Button A: Cursor UP
• press Button B: RETURN
• press Button C: Cursor Down

With hold functionality as well.

• hold Button A: toggle computer model (C64, C128, Vic-20, Apple 1, repeats)
• hold Button B: LOAD"*",8 / RUN for Commodore, snapshot system for Apple 1
• hold Button C: STOP

Thus, one can demonstrate the emulator loading a menu of programs, scrolling though the listing, and choosing one.  And toggle between the emulators.   The Apple 1 snapshot system allows choosing a snapshot and loading or saving it.

I support other hardware targets, and I have BLE pairing functionality.  So I am thinking of expanding support of the virtual buttons, including more virtual buttons, and providing 8-position joystick inputs (and button) too.  But for now, here is the documentation for the existing buttons.

And then just like that, the CoreS3, Tab5, and Sunton 7" now have more touch points implemented for their capacitive touch screens to allow for more virtual keys.