check in copy of Piotr Meyer's VM implementation for 65c816 as vm/nga-816

FossilOrigin-Name: a5c5ebaf691d78fc548dd7b69cd1f14f713abbf980a3f491f9321a9a6f14169e

RELEASE-NOTES

@@ -26,6 +26,11 @@
   - removed unused variables
   - use a struct for processor state, stacks
 
+- nga-816
+
+  - assembly implementation for 65c816
+  - by Piotr Meyer
+
 ## Examples
 
 - reduced some line lengths

vm/nga-816/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2021 Piotr Meyer
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

vm/nga-816/README.md

@@ -0,0 +1,17 @@
+# retro/816
+Port of [RETRO Forth](http://retroforth.org/) created
+by [Charles Childers](https://www.patreon.com/_crc) to 
+[C256 Foenix](https://c256foenix.com/), a retro-computer
+based on 65c816 CPU.
+
+This port is in infancy and there are dark and spooky things inside,
+but at this moment is able to run simple code in 1:1 pair to one of
+original interpreters (`vm/nga-c/barebones`).
+
+It runs in [Foenix IDE](https://github.com/Trinity-11/FoenixIDE), 
+it is also possible to run current, unmodified version of this 
+port on [go65c816 emulator](https://github.com/aniou/go65c816) 
+(use `retro.ini` parameters file here).
+
+## obligatory screenshot
+![sample run](Screenshot_20210222_213209.png)  

vm/nga-816/build.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+NAME=nga
+
+64tass -Wall -Wmacro-prefix -Wshadow --verbose-list -o ${NAME}.hex -L ${NAME}.lst --intel-hex --m65816 ${NAME}.asm

vm/nga-816/macros_inc.asm

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+; Set 8-bit accumulator
+setaxs          .macro
+                SEP #$30        ; set A&X short
+                .as
+                .xs 
+                .endm
+                
+; Set 16-bit accumulator
+setaxl          .macro
+                REP #$30        ; set A&X long 
+                .al
+                .xl
+                .endm
+
+; Set 8-bit accumulator
+setas           .macro
+                SEP #$20        ; set A short 
+                .as
+                .endm
+                
+; Set 16-bit accumulator
+setal           .macro
+                REP #$20        ; set A long 
+                .al
+                .endm
+
+; Set 8 bit index registers               
+setxs           .macro
+                SEP #$10        ; set X short 
+                .xs
+                .endm
+                
+; Set 16-bit index registers
+setxl           .macro
+                REP #$10        ; set X long 
+                .xl
+                .endm
+
+sdb         .macro          ; Set the B (Data bank) register
+            pha             ; begin setdbr macro
+            php
+            .setas
+            lda #\1
+            pha
+            plb
+            .databank \1
+            plp
+            pla             ; end setdbr macro
+            .endm
+