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+Atmel AVR Specific Information
+##############################
+
+This chapter discusses the AVR architecture dependencies in this
+port of RTEMS.
+
+**Architecture Documents**
+
+For information on the AVR architecture, refer to the following
+documents available from Atmel.
+
+TBD
+
+- See other CPUs for documentation reference formatting examples.
+
+CPU Model Dependent Features
+============================
+
+CPUs of the AVR 53X only differ in the peripherals and thus in the
+device drivers. This port does not yet support the 56X dual core variants.
+
+Count Leading Zeroes Instruction
+--------------------------------
+
+The AVR CPU has the XXX instruction which could be used to speed
+up the find first bit operation.  The use of this instruction should
+significantly speed up the scheduling associated with a thread blocking.
+
+Calling Conventions
+===================
+
+Processor Background
+--------------------
+
+The AVR architecture supports a simple call and return mechanism.
+A subroutine is invoked via the call (``call``) instruction.
+This instruction saves the return address in the ``RETS`` register
+and transfers the execution to the given address.
+
+It is the called funcions responsability to use the link instruction
+to reserve space on the stack for the local variables.  Returning from
+a subroutine is done by using the RTS (``RTS``) instruction which
+loads the PC with the adress stored in RETS.
+
+It is is important to note that the ``call`` instruction does not
+automatically save or restore any registers.  It is the responsibility
+of the high-level language compiler to define the register preservation
+and usage convention.
+
+Register Usage
+--------------
+
+A called function may clobber all registers, except RETS, R4-R7, P3-P5,
+FP and SP.  It may also modify the first 12 bytes in the callerâs stack
+frame which is used as an argument area for the first three arguments
+(which are passed in R0...R3 but may be placed on the stack by the
+called function).
+
+Parameter Passing
+-----------------
+
+RTEMS assumes that the AVR GCC calling convention is followed.
+The first three parameters are stored in registers R0, R1, and R2.
+All other parameters are put pushed on the stack.  The result is returned
+through register R0.
+
+Memory Model
+============
+
+The AVR family architecutre support a single unified 4 GB byte
+address space using 32-bit addresses. It maps all resources like internal
+and external memory and IO registers into separate sections of this
+common address space.
+
+The AVR architcture supports some form of memory
+protection via its Memory Management Unit. Since the
+AVR port runs in supervisior mode this memory
+protection mechanisms are not used.
+
+Interrupt Processing
+====================
+
+Discussed in this chapter are the AVR’s interrupt response and
+control mechanisms as they pertain to RTEMS.
+
+Vectoring of an Interrupt Handler
+---------------------------------
+
+TBD
+
+Disabling of Interrupts by RTEMS
+--------------------------------
+
+During interrupt disable critical sections, RTEMS disables interrupts to
+level N (N) before the execution of this section and restores them
+to the previous level upon completion of the section. RTEMS uses the
+instructions CLI and STI to enable and disable Interrupts. Emulation,
+Reset, NMI and Exception Interrupts are never disabled.
+
+Interrupt Stack
+---------------
+
+The AVR Architecture works with two different kind of stacks,
+User and Supervisor Stack. Since RTEMS and its Application run
+in supervisor mode, all interrupts will use the interrupted
+tasks stack for execution.
+
+Default Fatal Error Processing
+==============================
+
+The default fatal error handler for the AVR performs the following
+actions:
+
+- disables processor interrupts,
+
+- places the error code in *r0*, and
+
+- executes an infinite loop (``while(0);`` to
+  simulate a halt processor instruction.
+
+Symmetric Multiprocessing
+=========================
+
+SMP is not supported.
+
+Thread-Local Storage
+====================
+
+Thread-local storage is not supported due to a broken tool chain.
+
+Board Support Packages
+======================
+
+System Reset
+------------
+
+TBD
+
+.. COMMENT: COPYRIGHT (c) 1988-2006.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+