chat3.mu4

| This file is part of muforth: https://muforth.dev/
|
| Copyright 2002-2025 David Frech. (Read the LICENSE for details.)

| Calling this "chat3". It's really just an experiment to see if the style
| that I wrote the USB chat firmware in works in this context too. The main
| difference is that the original chat code was a big loop, where the USB
| "loop" was a subroutine - which meant that to return the "top" from any
| piece of code all you do is _return_. And using tail calls, it's easy to
| code in a Forth-like style that is very efficient.

loading S08 Chat v3 (target - tail-recursive version ;-)

hex
__meta

.ifdef in-ram  ram
.else

   trims    "14 allot      | ffac - ffbf: trims and security bytes
   vectors  "40 allot      | ffc0 - ffff
   | Memory code (wipe) has set boot and commit to reasonable defaults.
   commit

.then

| Compile the first 32 bits of the current muforth Git commit. When asked
| for the version, return these four bytes, in big-endian order.

label version
   muforth-commit drop 8 evaluate  >0123  c, c, c, c,

.ifndef in-ram  boot  .then

| The SCI code is identical between 908 and S08 except for the names - and
| offsets - of the SCI status and data regs ... so let's abstract them.

.ifdef S08

aka SCIS1 SciStatus
aka SCID  SciData

.else   | 908

aka SCS1 SciStatus
aka SCDR SciData

.then

label get-byte  ( returns char in A)
   begin  SciStatus 5 ( recvr full)  bset? until
   SciData ) lda  rts  ;c

label read-byte
   0 ,x lda  1 # aix  ( fall thru)  ;c

label put-byte  ( transmits char in A)
   begin  SciStatus 7 ( xmit empty)  bset? until
   SciData ) sta  rts  ;c

( chat3 protocol)

| Commands:
| 0  Idle       - ignored by chat; force other command loops to return to chat;
|                 can be used as an Idle
| 1  Version    - sets HX to point to version string:
|               - 4 bytes of muforth commit, big-endian
| 2  Run        - does an RTI - pops stack frame and runs
| 3  GetSP      - sets HX from SP, then returns HX
| 4  SetHX      - reads two bytes from SCI, writes them into H & X registers
| 5  ReadNext   - reads a byte from memory @ HX, writes it to SCI, incrs HX
| 6  WriteNext  - reads a byte from SCI, writes into memory @ HX, incrs HX
|
| ~~ The following are S08-only commands ~~
|
| 7  ReadN      - reads a count from SCI, reads that many bytes from
|                 memory, and writes them to SCI
| 8  FlashNext  - reads a byte from SCI, writes to flash @ HX, incrs HX
|               - calls a routine in ram that host downloads to device
|               - returns FSTAT



label process-serial
   SciStatus 5 ( recvr full)  bclr? if  rts  then  ( nothing to do)
   SciData ) lda  ( command)

   ( map 0 -> ff - ignore)

   .a decz? if ( Version)   version # ldhx  rts  then

   .a decz? if ( Run)   2 # ais ( skip return addr)  .h pul  rti  then

   .a decz? if ( GetSP)
      tsx  2 # aix ( skip return addr)
      .h psh  .a pul  put-byte c  ( send H)
                 txa  put-byte j  ( send X)  then

   .a decz? if ( SetHX)
      get-byte c  .a psh  .h pul  ( set H)
      get-byte c             tax  ( set X)  rts  then

   .a decz? if ( ReadNext)  read-byte j  then

   .a decz? if ( WriteNext)
      get-byte c   0 ,x sta  1 # aix

.ifdef S08

   ( end WriteNext)  rts  then

   .a decz? if ( ReadN)
      get-byte c  .a psh ( count)
      begin  read-byte c  0 ,s decz? until
      .a pul  rts  then

   .a decz? if ( FlashNext)
      get-byte c  flash-byte c  1 # aix  ( call flash routine in RAM)
      FSTAT ) lda  put-byte j

.then

   then
   ( unknown command)   rts  ;c

| If compiling into RAM and using 908 flash control block, check to make
| sure we haven't "run into" the control block, then jump forward over it
| and continue compiling there.

.def in-ram  .def control-block  .and .if
__host
: ?fits
   control-block  'zram @  u< if
      error" Code too long - ran into Flash control block"
   then ;
?fits
__meta
09c org           | continue compiling there
.then

| USB code defines its own versions of swi and clock code, so we needn't
| repeat them here.

.ifndef usb-debug-via-serial

.ifdef in-ram

label emulated-swi
   ( jsr/bsr has already pushed PC)
   .x psh  .a psh  tpa ( flags to A)  .a psh  sei

.else

Vswi handler

.then

   .h psh
.ifdef S08
   flash-command ) clr  ( do what we can to prevent spurious writes/erases)
.then
   begin  process-serial c  again  ;c

| If the chat interaction changes the PC on this stack frame to point
| somewhere other than _after_ the __swi, not all is lost - since we got
| here via a _call_ from reset, we'll return to _that_ loop, and re-enter
| the SWI.
|
| On the other hand, if the PC remains unaltered, an RTI from the SWI's
| stack frame wil simply return here, and we'll take the "exception" again.

label interact
.ifdef in-ram
   begin  emulated-swi c  again  ;c
.else
   begin  swi  again  ;c
.then

Vreset handler
   @ram #ram + # ldhx
   txs

.ifndef in-ram  ( don't compile clock/UART code for RAM-based versions)
ld target/S08/chat-init.mu4
.then

   begin  interact c  again  ;c

.then  ( usb-debug-via-serial)