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/byteread.asm

@@ -0,0 +1,81 @@
+; ***************************************************************************
+; 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_BYTEREAD_H
+#define AVR_MODULES_COM2W2_BYTEREAD_H
+
+
+.cseg
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w2RecvByteWaitForQuietClk
+;
+; Wait until the clock line is consistently high for 1ms.
+;
+; @clobbers r18, r20, r22
+
+com2w2RecvByteWaitForQuietClk:
+  ldi r18, 200
+com2w2RecvByteWaitForQuietClk_loop:
+      ldi r20, 100                                  ; wait up to 1ms for clock high (R20, R22)
+      rcall com2w2WaitForClockLowMulti10Us          ; (r20, r22)
+      brcs com2w2RecvByteWaitForQuietClk_waitForLow
+      dec r18
+    brne com2w2RecvByteWaitForQuietClk_loop
+    rjmp com2w2RecvByteWaitForQuietClk_ret
+com2w2RecvByteWaitForQuietClk_waitForLow:
+    ldi r20, 100                                    ; wait up to 1ms for clock low (R20, R22)
+    rcall com2w2WaitForClockLowMulti10Us
+    brcc com2w2RecvByteWaitForQuietClk_ret          ; not low within 1ms, assume line is quiet
+  brne com2w2RecvByteWaitForQuietClk_loop
+com2w2RecvByteWaitForQuietClk_ret:
+  ret
+
+
+
+; ---------------------------------------------------------------------------
+; @routine com2w2RecvByte
+;
+; @return CFLAG set if byte received, cleared on error
+; @return r16 byte received
+; @clobbers r17, r18, r20, r22
+
+com2w2RecvByte:
+  ldi r17, 8
+  clr r16
+com2w2RecvByte_loop:
+    ldi r20, 100                         ; wait up to 1ms for clock low
+    rcall com2w2WaitForClockLowMulti10Us  ; (R20, R22)
+    brcc com2w2RecvByte_end
+    ldi r20, 100                         ; wait up to 1ms for clock high
+    rcall com2w2WaitForClockHighMulti10Us ; (R20, R22)
+    brcc com2w2RecvByte_end
+    ; handle received bit
+    inr r18, COM_DATA_INPUT
+    andi r18, (1<<COM_DATA_PIN)
+    clc
+    breq com2w2RecvByte_clockData
+    sec
+com2w2RecvByte_clockData:
+    ror r16
+    dec r17
+  brne com2w2RecvByte_loop
+  sec
+com2w2RecvByte_end:
+  ret
+; @end
+
+
+
+
+#endif
+
+