chat-iic-core.mu4

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

loading AVR I2C chat (core)

__meta
hex

label restart
   u y movw  1 y sbiw  SPL yl out   | empty stack
   ( fall thru)  ;c

hook i2c-restart-hook


7 equ TWINT  ( bit#)  ( ack after all other actions)
6 equ TWEA   ( bit#)  ( enable receipt of slave address)
2 equ TWEN   ( bit#)

1 TWINT <<
1 TWEA  << or
1 TWEN  << or equ tw-reset


| comment
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| Status codes for slave receive mode:
|
|   60  own addr+write received and ACKed
|   80  prev addressed with own address; data byte recvd and ACKed
|   a0  STOP or repeated START received while in slave receive mode
|
| Status codes for slave transmit mode:
|
|   a8  own addr+read received and ACKed
|   b8  data byte xmitted and ACKed
|   c0  as above, but NACKed
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

| comment 
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| Register-use:
|
|   r0/r1              is used for writing flash (via SPM instruction)
|   r26/27 - aka x - is used for status and data bytes
|   r30/31 - aka z - is used to point to memory
|
|   These are also registers that are considered "scratch" by the
|   meta-compiler's conventions.
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

( Save and restore chat registers around the call to yield.)
( XXX Since this is used in only one place it could be inlined.)
label chat-yield
   z pushw  0 pushw  yield rcall  0 popw  z popw  ret  ;c

| Ack TWINT. Make sure TWEA and TWEN also set. Then Wait for TWINT; read
| status; mask prescaler bits; return status in xl. Clobbers xh.

label await-twint
   tw-reset xh ldi  TWCR xh sts  ( ack TWINT)
   begin  chat-yield rcall  TWCR xl lds  TWINT xl sbrs  again
   TWSR xl lds  0f8 xl andi  ret  ;c

label recv-byte
   await-twint rcall
   80 xl cpi  restart  0= until  ( restart protocol)
   TWDR xl lds  ret  ;c

| This is a bit tricky! Since the host had to send a new transaction for
| the read, on the first byte we're going to see _two_ interrupts: first,
| that while addressed as a slave receiver we got a STOP or RESTART; and
| second, that we were addressed as slave+read. We have to watch for, and
| ack, both.
|
| If we want to send multiple bytes back to the master, we have to look for
| and accept both a8 - addressed as slave+read - and b8 - byte transmitted
| and ACKed. Our caller can sit in a loop since the host will NACK the last
| byte, and we'll get a c0 status, and restart.

label expect-start
   await-twint rcall
   0a0 xl cpi  restart  0= until  ( we should see START/RESTART)
   ( fall thru)  ;c

| Returns to caller if either we were just addressed, or the last byte
| written was ACKed by the master.

label send-another?
   await-twint rcall
   0e8 xl andi  0a8 xl cpi  restart  0= until  ( match a8 and b8)  ret  ;c

| After sending byte and acking interrupt, wait for ACK/NACK and only
| return to caller if ok to send another byte.

label send-byte
   TWDR xl sts  send-another? rjmp  ;c

| As with the read-memory commands, we expect a start/restart to initiate
| the read.

label send-word
   x pushw  expect-start rcall
   xl pop  send-byte rcall  xl pop  send-byte rjmp  ;c

label recv-word
   recv-byte rcall  xl push
   recv-byte rcall  xl xh mov  xl pop  ret  ;c

( EEPROM read/write.)
ld target/AVR/eeprom.mu4

( Flash self-programming support.)
ld target/AVR/flash-self-prog.mu4

( Called by chat startup code.)
label serial-init
   ( Set I2C slave address from EEPROM)
   0 z ldiw  read-eeprom-byte rcall  1 invert xl andi  TWAR xl out

.def mega168  .def mega328  .or .if
   ( Set up SCL/SDA pins as inputs with pullups enabled: PC4 and PC5)
   xl clr  DDRC xl out  30 xl ldi  PORTC xl out

.else  ( prob mega164/324/644/1284)
   ( Set up SCL/SDA pins as inputs with pullups enabled: PC0 and PC1)
   xl clr  DDRC xl out  03 xl ldi  PORTC xl out

.then
   ret  ;c

| On reads, keep streaming bytes from memory to I2C as long as last byte
| was ACKed.

( Command routines.)
label read-data-cmd
   expect-start rcall
   begin    z+ xl ld  send-byte rcall  again  ;c

label read-flash-cmd
   expect-start rcall
   begin  pmz+ xl ld  send-byte rcall  again  ;c

label read-eeprom-cmd
   expect-start rcall
   begin  read-eeprom-byte rcall  1 z adiw  send-byte rcall  again  ;c

| When writing to data space - ram and i/o - keep streaming bytes from I2C
| into memory, until recv-byte gets something other than an 80 status.

label write-data-cmd
   begin  recv-byte rcall  z+ xl st  again  ;c

label write-eeprom-cmd
   begin  recv-byte rcall  write-eeprom-byte rcall  1 z adiw  again  ;c

label write-flash-cmd
   begin  recv-word rcall  x 0 movw  recv-byte rcall ( cmd)  do-spm rcall
          2 z adiw  again  ;c

( For chat dispatch loop.)
label recv-command-byte
   ( wait until addressed as slave+write)
   begin  await-twint rcall  60 xl cpi  0= until
   recv-byte rjmp  ( cmd)  ;c

( Load chat entry and command loop.)
ld target/AVR/chat-loop.mu4