avr: added com2w2 (slightly improved version of com2w).

- move IRQ control to main code (only the main code knows exactly which
  combination of pins is used for com2)
- split one big module into multiple smaller files (easier to maintain)

avr/modules/com2w2/msgread.asm

@@ -0,0 +1,71 @@
+; ***************************************************************************
+; copyright   : (C) 2026 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+#ifndef AVR_MODULES_COM2W2_MSGREAD_H
+#define AVR_MODULES_COM2W2_MSGREAD_H
+
+
+.cseg
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w2RecvMsg
+;
+; Receive a packet into buffer pointed to by X.
+; Expects interrupts to be disabled.
+;
+; @param R19 max buffer size
+; @param X   buffer to receive to
+; @return CFLAG set if msg received, cleared on error (see R16)
+; @return R16   if CFLAG cleared: 0=message not for this node, otherwise error
+; @clobbers r16, r17, r18, r19, r20, r22, r24, r25, X
+
+com2w2RecvMsg:
+  ; check buffer size
+  subi r19, 2
+  brcs com2w2RecvMsg_eBadSize
+  ; read destination address
+  rcall com2w2RecvByte                    ; (r17, r18, r20, r22)
+  brcc com2w2RecvMsg_eIo
+  st X+, r16
+  ; read remaining msg size
+  rcall com2w2RecvByte                    ; (r17, r18, r20, r22)
+  brcc com2w2RecvMsg_eIo
+  st X+, r16
+  inc r16                                 ; account for CRC byte
+  sub r19, r16
+  brcs com2w2RecvMsg_eBadSize
+  mov r19, r16
+com2w2RecvMsg_loop:
+    rcall com2w2RecvByte                  ; (r17, r18, r20, r22)
+    brcc com2w2RecvMsg_eIo
+    st X+, r16
+    dec r19
+  brne com2w2RecvMsg_loop
+  sec
+  rjmp com2w2RecvMsg_end
+com2w2RecvMsg_eBadSize:
+  ldi r16, NET_IFACE_OFFS_ERR_MSGSIZE_LOW
+  rjmp com2w2RecvMsg_incCounterRet
+com2w2RecvMsg_eIo:
+  ldi r16, NET_IFACE_OFFS_ERR_IO_LOW
+com2w2RecvMsg_incCounterRet:
+  rcall NET_Interface_IncCounter16         ; (R24, R25)
+  rcall com2w2RecvByteWaitForQuietClk      ; (r18, r20, r22)
+com2w2RecvMsg_clcRet:
+  clc
+com2w2RecvMsg_end:
+  ret
+; @end
+
+
+
+
+#endif
+