# Neon816

This is a port to Lenore Byron's [Neon816](https://hackaday.io/project/164325-neon816) system.  The Neon816 Developer
Edition ships with a small 16-bit Forth.

OF816 for the Neon816 is configured to run as an alternative firmware out of bank $20.  With a little ajustment, it 
could be configured to run out of bank $21 (but starting it is an excercise for the reader).

It configures the MMU and serial port like NeonFORTH does.  The direct page, stack, and return stack occupy the first
$400 bytes of RAM.

To build OF816 for the Neon816, change to the platform directory and run
``build.sh``. It will output a 64K binary named ``of816-neon.bin`` that can be flashed into the Neon's firmware.
See below for installation instructions.

## Port Features

Hardware access words with the same semantics as NeonFORTH are found in the NEON816 dictionary.

The hardware access dictionary is currently not complete but has the words for accessing the PS/2 ports, I2C2,
and VDC.

Execute ``also neon816`` to gain access to the words.

See the [Neon816 Manual](https://cdn.hackaday.io/files/1643257030480800/sysmanual.pdf) for descriptions of the
specific words.

## Installation / Removal

The instructions assume you are running Linux.  The Neon firmware loader is supported under Linux only.

### Installing OF816

**THIS WILL OVERWRITE THE NEON'S ORIGINAL FIRMWARE!**

**IT IS STRONGLY RECOMMENDED YOU BACK UP THE ORIGINAL FIRMWARE!** (see below)

**READ _ALL_ OF THE FOLLOWING BEFORE PROCEEDING AND DO NOT PROCEED IF ANY OF THIS MAKES YOU UNCOMFORTABLE!**

After building the firmware image, the image must be converted to Intel Hex format.  I like the bin2hex tool originally
found [here](https://grumpf.hope-2000.org) (page is in German), also in my [Github repo](https://github.com/mgcaret/bin2hex).
Build the ``bin2hex`` binary and execute:  ``bin2hex of816-neon.bin > of816-neon.hex`` 

Once you have the .hex file, you will need to use the [Neon firmware loader](https://hackaday.io/project/164325-neon816)
to install the image.  This requires an FTDI cable connected to the 3.3V UART header on the Neon816 system board.

To back up the original firmware, you will need to add an additional command routine to neonprog.cpp (add it after the
write command):

```
   else if(!strcmp(cmd,"dumprom")) {
        char* fn=strtok(nullptr," ");
        char buf[0x40];
        if(!fn) return;
        auto st=Releaser(
            fopen(fn,"w"),
            [](auto f){if(f) fclose(f);});
        if(!st) {
            printf("Could not open file\n");
            return;
        }
        for (int addr=0x200000; addr<0x220000; addr+=sizeof(buf)) {
            writeHex(addr>>16,2); writeChar(':');
            writeHex(addr,4); writeChar('#');
            for (int i=0; i<sizeof(buf); i++) {
                writeChar('@');
                unsigned char c=readByte();
                buf[i]=c;
            }
            fwrite(&buf, sizeof(buf), 1, st);
            printf("%08X\n",addr);
        }
    }
```

build neonprog then start it with ``neonprog /dev/ttyUSBx`` (replace device with actual serial device for FTDI cable.

From within neonprog, execute ``dumprom backup.bin`` to save an image of both ROM banks to ``backup.bin``.

Once the backup has finished (it will take a while), you can proceed to the installation of OF816 with 
``flash of816-neon.hex``.  This will also take a while.  When it is done, reset your Neon and OF816 should start.

### Restoring the Original NeonFORTH Firmware

Since the Neon (at the time of this writing) only ships with the first bank of flash occupied, first, split your backup
with ``split -b 65536 backup.bin``.  This will output two files, ``xaa`` and ``xab`` that are bank $20 and bank $21,
respectively.  Then run ``bin2hex xaa > neonforth.hex``.  You can then flash this with neonprog using
``flash neonforth.hex``.   Once it's done, reset your Neon and you should see the original firmware running.

## A Comparison of OF816 and NeonFORTH

NeonFORTH, which comes with the Neon816, is a compact 16-bit Forth specifically designed for the system by its creator.

OF816 is a portable 32-bit Forth that is designed to run on many 65816 systems.  As a result of its 32-bit cells, it has
a flat view of the 65816 address space.  A negative consequence is that it is slower and uses more memory than a system
like NeonFORTH.

A general comparison:

| OF816                                    | NeonFORTH                                    |
|------------------------------------------|----------------------------------------------|
| 32-bit cells                             | 16-bit cells                                 |
| First-class access to '816 address space | Special words to access memory beyond bank 0 |
| Slower                                   | Faster                                       |
| More RAM/ROM use                         | Less RAM/ROM use                             |
| ANSI standard Forth                      | Not ANSI standard                            |
| FCode support                            | No FCode support                             |
| Larger dictionary                        | Smaller dictionary                           |

Additionally, as NeonFORTH is maintained by the creator of the Neon816, it is going to have features specific to the
Neon816 sooner than OF816 will have them.

Overall, NeonFORTH is small, and well suited to basic experiments with the Neon816's hardware.  OF816 is more powerful
in the large built-in dictionary, and in the way it handles numbers, address space, exceptions, and stack over/
underflow.  However, this makes it slower and use more memory.