diff --git a/avr/modules/uart_hw/defs.asm b/avr/modules/uart_hw/defs.asm
index 1eb33a2..370457d 100644
--- a/avr/modules/uart_hw/defs.asm
+++ b/avr/modules/uart_hw/defs.asm
@@ -12,11 +12,17 @@
 .equ UART_HW_IFACE_WRITEBUF_SIZE       = 8
 
 
+.equ UART_HW_BUFFER_INUSE_BIT          = 7
+.equ UART_HW_BUFFER_IFACENUM1_BIT      = 1
+.equ UART_HW_BUFFER_IFACENUM0_BIT      = 0
+
+
 .equ UART_HW_MODE_OFF                  = 0
 .equ UART_HW_MODE_IDLE                 = 1
 .equ UART_HW_MODE_READING              = 2
 .equ UART_HW_MODE_WRITING              = 4
 .equ UART_HW_MODE_SKIPPING             = 8
+.equ UART_HW_MODE_WAITATTNLOW          = 16   ; waiting after setting ATTN low
 
 
 .equ UART_HW_STATUS_UNDERRUN           = 0x01
@@ -26,14 +32,16 @@
 .equ UART_HW_STATUS_ATTN               = 0x80
 
 
-.equ UART_HW_IFACE_OFFS_MODE            = 0
-.equ UART_HW_IFACE_OFFS_STATUS          = 1
-.equ UART_HW_IFACE_OFFS_READTIMER       = 2
-.equ UART_HW_IFACE_OFFS_WRITETIMER      = 3
-.equ UART_HW_IFACE_OFFS_ERR_OVR         = 4
+.equ UART_HW_IFACE_OFFS_IFACENUM        = 0 ; interface number (put into received messages)
+.equ UART_HW_IFACE_OFFS_MODE            = 1
+.equ UART_HW_IFACE_OFFS_STATUS          = 2
+.equ UART_HW_IFACE_OFFS_READTIMER       = 3
+.equ UART_HW_IFACE_OFFS_WRITETIMER      = 4
+.equ UART_HW_IFACE_OFFS_ERR_OVR         = 5
+.equ UART_HW_IFACE_OFFS_ERR_CONTENT     = 6
 
   ; ringbuffer for incoming chars
-.equ UART_HW_IFACE_OFFS_READBUF         = 5
+.equ UART_HW_IFACE_OFFS_READBUF         = 7
 .equ UART_HW_IFACE_OFFS_READBUF_MAX     = UART_HW_IFACE_OFFS_READBUF
 .equ UART_HW_IFACE_OFFS_READBUF_USED    = UART_HW_IFACE_OFFS_READBUF+1
 .equ UART_HW_IFACE_OFFS_READBUF_RDPOS   = UART_HW_IFACE_OFFS_READBUF+2
diff --git a/avr/modules/uart_hw/init_uart1.asm b/avr/modules/uart_hw/init_uart1.asm
deleted file mode 100644
index 23b699b..0000000
--- a/avr/modules/uart_hw/init_uart1.asm
+++ /dev/null
@@ -1,46 +0,0 @@
-; ***************************************************************************
-; copyright   : (C) 2025 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.   *
-; ***************************************************************************
-
-
-
-
-.cseg
-
-
-
-; ---------------------------------------------------------------------------
-; @routine UART_HW_Uart1_Init @global
-;
-; @param Y pointer to interface data in SRAM (see @ref UART_HW_IFACE_OFFS_STATE)
-; @clobbers R16, R17, X
-
-UART_HW_Uart1_Init:
-  rcall UART_HW_InitInterface
-
-  ; set baudrate
-.if clock == 8000000
-  ldi r16, 25 ; (19.2Kb/s at 8MHz)
-  ldi r17, 0
-.endif
-
-.if clock == 1000000
-  ldi r16, 2  ; (19.2Kb/s at 1MHz)
-  ldi r17, 0  
-.endif
-
-  out UBRR1H, r17
-  out UBRR1L, r16
-
-  ; set character format 
-  ldi r16, (1<<USBS1)|(3<<UCSZ10)
-  out UCSR1C, r16
-
-  ret
-; @end
-
diff --git a/avr/modules/uart_hw/lowlevel_uart1.asm b/avr/modules/uart_hw/lowlevel_uart1.asm
index 439ddfa..6d30e94 100644
--- a/avr/modules/uart_hw/lowlevel_uart1.asm
+++ b/avr/modules/uart_hw/lowlevel_uart1.asm
@@ -13,6 +13,38 @@
 
 
 
+; ---------------------------------------------------------------------------
+; @routine UART_HW_Uart1_Init @global
+;
+; @param Y pointer to interface data in SRAM (see @ref UART_HW_IFACE_OFFS_STATE)
+; @clobbers R16, R17, X
+
+UART_HW_Uart1_Init:
+  rcall UART_HW_InterfaceInit
+
+  ; set baudrate
+.if clock == 8000000
+  ldi r16, 25 ; (19.2Kb/s at 8MHz)
+  ldi r17, 0
+.endif
+
+.if clock == 1000000
+  ldi r16, 2  ; (19.2Kb/s at 1MHz)
+  ldi r17, 0  
+.endif
+
+  sts UBRR1H, r17
+  sts UBRR1L, r16
+
+  ; set character format 
+  ldi r16, (1<<USBS1)|(3<<UCSZ10)
+  sts UCSR1C, r16
+
+  ret
+; @end
+
+
+
 ; ---------------------------------------------------------------------------
 ; @routine UART_HW_Uart1_StartRx @global
 ;
@@ -112,7 +144,13 @@ UART_HW_Uart1_TxCharIsr:
   sbrs r16,UDRE1
     rjmp UART_HW_Uart1_TxCharIsr_end           ; not ready
   rcall UART_HW_InterfaceReadFromWriteBuffer   ; (R17, R18, X)
-  brcs UART_HW_Uart1_TxCharIsr_send            ; no data in buffer
+  brcs UART_HW_Uart1_TxCharIsr_send            ; got a byte, go send
+
+  ; disable further DRE1 interrupts
+  lds r16, UCSR1B
+  cbr r16, (1<<UDRIE1)                         ; disable TX data register empty interrupt
+  sts UCSR1B, r16
+  ; set underrun status (TODO: maybe change this later)
   ldd r16, Y+UART_HW_IFACE_OFFS_STATUS         ; set underrun error
   ori r16, UART_HW_STATUS_UNDERRUN
   std Y+UART_HW_IFACE_OFFS_STATUS, r16
diff --git a/avr/modules/uart_hw/msglevel_recv.asm b/avr/modules/uart_hw/msglevel_recv.asm
index cac2516..362d258 100644
--- a/avr/modules/uart_hw/msglevel_recv.asm
+++ b/avr/modules/uart_hw/msglevel_recv.asm
@@ -10,75 +10,79 @@
 
 .cseg
 
+; ---------------------------------------------------------------------------
+; @routine UART_HW_Interface_RunRead
+;
+; This routine reads bytes from the ringbuffer of the given
+; interface and parses them into messages.
+; If a valid message is received it will be added to the system's
+; incoming message ringbuffer.
+;
+; @param Y   pointer to start of interface data
+; @param X   pointer to start of buffer
+; @param r16 buffer number
+; @clobbers R16, R17, R18, R19, R20, R21, X
 
 UART_HW_Interface_RunRead:
-  rcall uartHwReadEnsureBuffer                  ; (r16, R17, X)
-  brcc UART_HW_Interface_RunRead_end
-  rcall uartHwReadEnsureHeader                  ; (r16, r17, r20, r21, X)
-  brcc UART_HW_Interface_RunRead_end
-  rcall uartHwReadEnsureBody                    ; (r16, r17, r20, r21, x)
-  brcc UART_HW_Interface_RunRead_end
-UART_HW_Interface_RunRead_HaveMsg:
+  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_BUFNUM
+  cpi r16, 0xff
+  brne UART_HW_Interface_RunRead_HaveBuffer
+  rcall uartHwAllocateReadBuffer                ; (r16, R17, X)
+  brcc UART_HW_Interface_RunRead_ovrError
+  rcall uartHwReadSetBuffer                     ; (r16)
+UART_HW_Interface_RunRead_HaveBuffer:
+  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_LEFT
+  tst r16
+  brne UART_HW_Interface_RunRead_HaveHeader
   ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_USED
-  cpi r16, 3
-  brcs UART_HW_Interface_RunRead_badMsg
-  ; check and store msg
+  ldi r20, 2
+  sub r20, r16
+  rcall uartHwReadUptoNumBytes                  ; (r16, r17, r20, r21, X)
+  tst r20
+  brne UART_HW_Interface_RunRead_end
+  ldd xl, Y+UART_HW_IFACE_OFFS_READMSG_PTR
+  ldd xh, Y+UART_HW_IFACE_OFFS_READMSG_PTR+1
+  sbiw xh:xl, 1
+  ld r16, X                                     ; msg len
+  cpi r16, UART_HW_FIXEDBUFFERS_SIZE-4          ; minus buffer status byte, dest addr, msglen, crc
+  brcc UART_HW_Interface_RunRead_dataError      ; invalid msg
+  inc r16
+  std Y+UART_HW_IFACE_OFFS_READMSG_LEFT, r16
+UART_HW_Interface_RunRead_HaveHeader:
+  ldd r20, Y+UART_HW_IFACE_OFFS_READMSG_LEFT
+  tst r20
+  breq UART_HW_Interface_RunRead_HaveMsg
+  rcall uartHwReadUptoNumBytes                  ; (r16, r17, r20, r21, X)
+  tst r20
+  brne UART_HW_Interface_RunRead_end            ; not all bytes received, done for now
+UART_HW_Interface_RunRead_HaveMsg:
+  ldd xl, Y+UART_HW_IFACE_OFFS_READMSG_PTR
+  ldd xh, Y+UART_HW_IFACE_OFFS_READMSG_PTR+1
+  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_USED
+  sub xl, r16                                   ; X-=r16
+  sbc xh, r16
+  add xh, r16
+  rcall com2CheckMessageInBuffer                ; (R16, R17, R18, R19, R20, X)
+  brcc UART_HW_Interface_RunRead_dataError
   ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_BUFNUM
   rcall UART_HW_AddIncomingMsgNum               ; (R17, R18, X)
-  brcs UART_HW_Interface_RunRead_clearBuf
-  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_BUFNUM
-  rcall UART_HW_FixedBuffers_ReleaseByNum       ; (R16, X)
-UART_HW_Interface_RunRead_clearBuf:
+  brcc UART_HW_Interface_RunRead_ovrError
   ldi r16, 0xff
   std Y+UART_HW_IFACE_OFFS_READMSG_BUFNUM, r16
   rjmp UART_HW_Interface_RunRead_end
-UART_HW_Interface_RunRead_badMsg:
-  ; reset READ buffer settings, enter skip mode
-  rcall uartHwResetBufferStartSkipping          ; (r16, X)
+UART_HW_Interface_RunRead_ovrError:
+  rcall uartHwIncOvrCounter
+  rcall uartHwReadResetBuffer
+  rjmp UART_HW_Interface_RunRead_end
+UART_HW_Interface_RunRead_dataError:
+  rcall uartHwIncContentCounter
+  rcall uartHwResetBufferStartSkipping
 UART_HW_Interface_RunRead_end:
   ret
 ; @end
 
 
 
-; ---------------------------------------------------------------------------
-; @routine uartHwEnsureReadBuffer
-;
-; @param Y pointer to start of interface data
-; @clobbers r16 (R17, X)
-
-uartHwReadEnsureBuffer:
-  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_BUFNUM
-  cpi r16, 0xff
-  breq uartHwReadEnsureBuffer_alloc
-uartHwReadEnsureBuffer_SecRet:
-  sec
-  ret
-uartHwReadEnsureBuffer_alloc:
-  rcall uartHwAllocateReadBuffer                ; (r16, R17, X)
-  brcc uartHwReadEnsureBuffer_error
-  rcall uartHwReadSetBuffer                     ; (r16)
-  rjmp uartHwReadEnsureBuffer_SecRet
-uartHwReadEnsureBuffer_error:
-  ; no buffer, set error status, skip msg
-  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_BUFNUM
-  rcall UART_HW_FixedBuffers_Locate             ; (r16)
-  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_BUFNUM
-  rcall uartHwReadResetBuffer                   ; (r16)
-  ldd r16, Y+UART_HW_IFACE_OFFS_MODE
-  ori r16, UART_HW_MODE_SKIPPING
-  std Y+UART_HW_IFACE_OFFS_MODE, r16
-  ldd r16, Y+UART_HW_IFACE_OFFS_ERR_OVR
-  inc r16
-  breq UART_HW_Interface_RunRead_end
-  std Y+UART_HW_IFACE_OFFS_ERR_OVR, r16
-  clc
-uartHwReadEnsureBuffer_end:
-  ret
-; @end
-
-
-
 ; ---------------------------------------------------------------------------
 ; @routine uartHwReadSetBuffer
 ;
@@ -108,8 +112,12 @@ uartHwReadSetBuffer:
 ; @clobbers r16, X
 
 uartHwReadResetBuffer:
-  ; reset READ buffer settings, enter skip mode
+  ; reset READ buffer settings
   ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_BUFNUM
+  cpi r16, 0xff
+  brne uartHwReadResetBuffer_haveBuffer
+  ret
+uartHwReadResetBuffer_haveBuffer:
   rcall UART_HW_FixedBuffers_Locate            ; (X)
   ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_BUFNUM
   rjmp uartHwReadSetBuffer                     ; (r16)
@@ -134,64 +142,20 @@ uartHwResetBufferStartSkipping:
 
 
 
-; ---------------------------------------------------------------------------
-; @routine uartHwReadEnsureHeader
-;
-; @param Y pointer to start of interface data
-; @clobbers r16 (r17, r20, r21, X)
-
-uartHwReadEnsureHeader:
-  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_LEFT
-  tst r16
-  breq uartHwReadEnsureHeader_readHeader
-  sec
-  ret
-uartHwReadEnsureHeader_readHeader:
-  ; read and validate header (2 bytes)
-  rcall uartHwReadAndValidateHeader             ; (r16, r17, r20, r21, X)
-  brcc UART_HW_Interface_RunRead_badMsg
-  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_USED
-  cpi r16, 2                                    ; full header in buffer (2 bytes)?
-  brcs UART_HW_Interface_RunRead_end            ; nope, done for this round
-uartHwReadEnsureHeader_end:
-  ret
-; @end
-
-
-
-; ---------------------------------------------------------------------------
-; @routine uartHwReadEnsureBody
-;
-; @param Y pointer to start of interface data
-; @clobbers r20 (r16, r17, r21, x)
-
-uartHwReadEnsureBody:
-  ldd r20, Y+UART_HW_IFACE_OFFS_READMSG_LEFT
-  tst r20
-  sec
-  breq uartHwReadEnsureBody_end                 ; no bytes left, message done
-  rcall uartHwReadUptoNumBytes                  ; (r16, r17, r20, r21, X)
-  ldd r20, Y+UART_HW_IFACE_OFFS_READMSG_LEFT              
-  tst r20
-  sec
-  breq uartHwReadEnsureBody_end                 ; no bytes left, message done
-  clc
-uartHwReadEnsureBody_end:
-  ret
-; @end
-
-
-
 ; ---------------------------------------------------------------------------
 ; @routine uartHwAllocateReadBuffer
 ;
+; @return CFLAG set if buffer set, cleared otherwise
 ; @param Y pointer to start of interface data
-; @clobbers r16 (R17, X)
+; @clobbers r16, R17 (X)
 
 uartHwAllocateReadBuffer:
   rcall UART_HW_FixedBuffers_Alloc              ; (R16, R17, X)
   brcc uartHwAllocateReadBuffer_end
   std Y+UART_HW_IFACE_OFFS_READMSG_BUFNUM, r16
+  ldd r17, Y+UART_HW_IFACE_OFFS_IFACENUM
+  ori r17, (1<<UART_HW_BUFFER_INUSE_BIT)
+  st X, r17
   adiw xh:xl, 1
   std Y+UART_HW_IFACE_OFFS_READMSG_PTR, xl
   std Y+UART_HW_IFACE_OFFS_READMSG_PTR+1, xh
@@ -205,47 +169,10 @@ uartHwAllocateReadBuffer_end:
 
 
 
-
-; ---------------------------------------------------------------------------
-; @routine uartHwReadAndValidateHeader
-;
-; @param Y pointer to start of interface data
-; @clobbers r16, r20, X (r17, r21)
-
-uartHwReadAndValidateHeader:
-  ; read until we have 2 bytes
-  ldi r20, 2
-  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_USED
-  sub r20, r16
-  rcall uartHwReadUptoNumBytes                        ; (r16, r17, r20, r21, X)
-  ; check whether we have 2 bytes
-  ldd r16, Y+UART_HW_IFACE_OFFS_READMSG_USED
-  cpi r16, 2
-  brcs uartHwReadAndValidateHeader_ok                 ; < 2 bytes in buffer, nothing to do
-  ; read and check msg len
-  ldd xl, Y+UART_HW_IFACE_OFFS_READMSG_PTR
-  ldd xh, Y+UART_HW_IFACE_OFFS_READMSG_PTR+1
-  sbiw xh:xl, 1                                       ; go back one byte, pointing to MSG_LEN
-  ld r16, X
-  cpi r16, UART_HW_FIXEDBUFFERS_SIZE-4                ; minus buffer status byte, dest addr, msglen, crc
-  brcc uartHwReadAndValidateHeader_error              ; bad msg length
-  ; set number of bytes left to read
-  inc r16                                             ; account for crc byte
-  std Y+UART_HW_IFACE_OFFS_READMSG_LEFT, r16
-uartHwReadAndValidateHeader_ok:
-  sec
-  ret
-uartHwReadAndValidateHeader_error:
-  clc
-  ret
-; @end
-
-
-
-
 ; ---------------------------------------------------------------------------
 ; @routine uartHwReadUptoNumBytes
 ;
+; @return r20 remaining bytes (bytes not yet read)
 ; @param Y pointer to start of interface data
 ; @param R20  number of bytes to read
 ; @clobbers r16, r20, r21, X (R17)
@@ -278,3 +205,39 @@ uartHwReadUptoNumBytes_done:
 ; @end
 
 
+
+; ---------------------------------------------------------------------------
+; @routine uartHwIncOvrCounter
+;
+; @param Y pointer to start of interface data
+; @clobbers r16
+
+uartHwIncOvrCounter:
+  ldd r16, Y+UART_HW_IFACE_OFFS_ERR_OVR
+  inc r16
+  breq uartHwIncOvrCounter_end
+  std Y+UART_HW_IFACE_OFFS_ERR_OVR, r16
+uartHwIncOvrCounter_end:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine uartHwIncContentCounter
+;
+; @param Y pointer to start of interface data
+; @clobbers r16
+
+uartHwIncContentCounter:
+  ldd r16, Y+UART_HW_IFACE_OFFS_ERR_CONTENT
+  inc r16
+  breq uartHwIncContentCounter_end
+  std Y+UART_HW_IFACE_OFFS_ERR_OVR, r16
+uartHwIncContentCounter_end:
+  ret
+; @end
+
+
+
+
diff --git a/avr/modules/uart_hw/msglevel_send.asm b/avr/modules/uart_hw/msglevel_send.asm
index a43ea31..26c53d4 100644
--- a/avr/modules/uart_hw/msglevel_send.asm
+++ b/avr/modules/uart_hw/msglevel_send.asm
@@ -14,33 +14,23 @@
 ; ---------------------------------------------------------------------------
 ; @routine UART_HW_Interface_RunWrite @global
 ;
+; Get messages via @ref UART_HW_GetNextOutgoingMsgNum and fill them into
+; the outbound ringbuffer of this interface.
+;
 ; @param Y pointer to start of interface data
 ; @clobbers r16, r19, X (R17, R18, R20, R21)
 
 UART_HW_Interface_RunWrite:
   ldd r19, Y+UART_HW_IFACE_OFFS_WRITEMSG_BUFNUM
   cpi r19, 0xff
-  brne UART_HW_Interface_RunWrite_haveMsg
-  rcall UART_HW_GetNextOutgoingMsgNum            ; (R17, R18, X)
-  rcall UART_HW_FixedBuffers_Locate              ; (R16)
-  brcc UART_HW_Interface_RunWrite_end
-  std Y+UART_HW_IFACE_OFFS_WRITEMSG_BUFNUM, r19
-  adiw xh:xl, 1
-  std Y+UART_HW_IFACE_OFFS_WRITEMSG_PTR, xl
-  std Y+UART_HW_IFACE_OFFS_WRITEMSG_PTR+1, xh
-  adiw xh:xl, 1                                  ; get msg len
-  ld r16, X
-  inc r16
-  inc r16
-  inc r16
-  std Y+UART_HW_IFACE_OFFS_WRITEMSG_LEFT, r16
-  std Y+UART_HW_IFACE_OFFS_WRITEMSG_USED, r16
+  breq UART_HW_Interface_RunWrite_end            ; nothing to do
 UART_HW_Interface_RunWrite_haveMsg:
   ldd r20, Y+UART_HW_IFACE_OFFS_WRITEMSG_LEFT
   rcall uartHwWriteUptoNumBytes                  ; (r16, r17, r18, r20, r21, X)
   ldd r16, Y+UART_HW_IFACE_OFFS_WRITEMSG_LEFT
   tst r16
   brne UART_HW_Interface_RunWrite_end            ; still bytes left to write
+; message completely sent to interface, release buffer
   ldd r16, Y+UART_HW_IFACE_OFFS_WRITEMSG_BUFNUM
   rcall UART_HW_FixedBuffers_ReleaseByNum
   ldi r16, 0xff                                  ; reset buffer number
@@ -51,6 +41,35 @@ UART_HW_Interface_RunWrite_end:
 
 
 
+; ---------------------------------------------------------------------------
+; @routine UART_HW_Interface_WriteSetBuffer
+;
+; Set given fixed buffer as source for @ref UART_HW_Interface_RunWrite.
+;
+; @param r16 buffer num
+; @clobbers r16, r19, X
+
+UART_HW_Interface_WriteSetBuffer:
+  mov r19, r16
+  rcall UART_HW_FixedBuffers_Locate              ; (R16)
+  brcc UART_HW_Interface_WriteSetBuffer_end
+  std Y+UART_HW_IFACE_OFFS_WRITEMSG_BUFNUM, r19
+  adiw xh:xl, 1
+  std Y+UART_HW_IFACE_OFFS_WRITEMSG_PTR, xl
+  std Y+UART_HW_IFACE_OFFS_WRITEMSG_PTR+1, xh
+  adiw xh:xl, 1                                  ; get msg len
+  ld r16, X
+  inc r16                                        ; adjust for destination addr byte
+  inc r16                                        ; adjust for msg len byte
+  inc r16                                        ; adjust for crc byte
+  std Y+UART_HW_IFACE_OFFS_WRITEMSG_LEFT, r16
+  std Y+UART_HW_IFACE_OFFS_WRITEMSG_USED, r16
+UART_HW_Interface_WriteSetBuffer_end:
+  ret
+; @end
+
+
+
 ; ---------------------------------------------------------------------------
 ; @routine uartHwWriteUptoNumBytes
 ;
@@ -84,3 +103,4 @@ uartHwWriteUptoNumBytes_done:
 
 
 
+