forked from Imagelibrary/rtems
ffae7bd65f
* ada_user/Makefile.am, ada_user/ada_user.texi, cpu_supplement/Makefile.am, cpu_supplement/cpu_supplement.texi, cpu_supplement/sparc.t: Add Blackfin CPU supplement chapter and get everything building from previous breakages. * cpu_supplement/bfin.t: New file.
201 lines
6.3 KiB
Perl
201 lines
6.3 KiB
Perl
@c
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@c COPYRIGHT (c) 1988-2006.
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@c On-Line Applications Research Corporation (OAR).
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@c All rights reserved.
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@c
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@c $Id$
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@c
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@ifinfo
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@end ifinfo
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@chapter Blackfin Specific Information
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This chapter discusses the Blackfin architecture dependencies
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in this port of RTEMS.
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@subheading Architecture Documents
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For information on the Blackfin architecture,
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refer to the following documents available from
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Analog Devices.
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TBD
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@c @itemize @bullet
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@c @item @cite{"ADSP-BF533 Blackfin Processor Hardware Reference."
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@c @file{http://www.analog.com/UploadedFiles/Associated_Docs/892485982bf533_hwr.pdf}
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@c
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@c @end itemize
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@section CPU Model Dependent Features
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CPUs of the Blackfin 53X only differ in the perifericals
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and thus in the device drivers. This port does not yet
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support the 56X dual core variants.
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@subsection CPU Model Name
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The macro @code{CPU_MODEL_NAME} is a string which designates
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the architectural level of this CPU model. The following is
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a list of the settings for this string based upon @code{gcc}
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CPU model predefines:
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@example
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"BF533"
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@end example
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@subsection Count Leading Zeroes Instruction
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The Blackfin CPU has the BITTST instruction
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which could be used to speed up the find first bit
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operation. The use of this instruction should significantly speed up
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the scheduling associated with a thread blocking.
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@subsection Floating Point Unit
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The macro BF_HAS_FPU is set to 0 to indicate that
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this CPU model has no hardware floating point unit.
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Blackfin CPUs don't have floating point so
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@section Calling Conventions
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Each high-level language compiler generates
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subroutine entry and exit code based upon a set of rules known
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as the compiler's calling convention. These rules address the
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following issues:
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@itemize @bullet
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@item register preservation and usage
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@item parameter passing
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@item call and return mechanism
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@end itemize
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A compiler's calling convention is of importance when
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interfacing to subroutines written in another language either
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assembly or high-level. Even when the high-level language and
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target processor are the same, different compilers may use
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different calling conventions. As a result, calling conventions
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are both processor and compiler dependent.
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This section is heavily based on content taken from the
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Blackfin uCLinux documentation wiki which is edited
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by Analog Devices and Arcturus Networks.
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@file{http://docs.blackfin.uclinux.org/}
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@subsection Processor Background
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The Blackfin architecture supports a simple call and return mechanism.
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A subroutine is invoked via the call (@code{call}) instruction.
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This instruction saves the return address in the @code{RETS} register
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and transfers the execution to the given address.
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It is the called funcions responsability to use the link instruction to
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reserve space on the stack for the local variables.
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Returning from a subroutine is done by using the RTS (@code{RTS})
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instruction which loads the PC with the adress stored in RETS.
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It is is important to note that the @code{call} instruction does not
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automatically save or restore any registers. It is the
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responsibility of the high-level language compiler to define the
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register preservation and usage convention.
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@subsection Register Usage
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A called function may clobber all registers, except RETS, R4-R7, P3-P5, FP and SP.
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It may also modify the first 12 bytes in the caller’s stack frame which is used as
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an argument area for the first three arguments (which are passed in R0...R3 but may
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be placed on the stack by the called function).
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@subsection Parameter Passing
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RTEMS assumes that the Blackfin GCC calling convention is followed.
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The first three parameters are stored in registers R0, R1, and R2.
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All other parameters are put pushed on the stack.
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The result is returned through register R0.
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@subsection User-Provided Routines
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All user-provided routines invoked by RTEMS, such as
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user extensions, device drivers, and MPCI routines, must also
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adhere to these calling conventions.
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@section Memory Model
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The Blackfin family architecutre support a single unified 4
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G byte address space using 32-bit addresses. It maps all
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resources like internal and external memory and IO registers
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into separate sections of this common address space.
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The Blackfin architcture supporst some form of memory
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protection via its Memory Management Unit. Since the
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Blackfin port runs in supervisior mode this memory
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protection mechanisms are not used.
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@section Interrupt Processing
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Discussed in this chapter are the Blackfin's
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interrupt response and control mechanisms as they pertain to
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RTEMS. The Blackfin architecture support 16 kinds of
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interrupts broken down into Core and general-purpose
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interrupts.
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@subsection Vectoring of an Interrupt Handler
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RTEMS maps levels 0 -15 directly to Blackfins event
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vectors EVT0 - EVT15. Since EVT0 - EVT6 are core
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events and it is suggested to use EVT15 and EVT15 for
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Software interrupts, 7 Interrupts (EVT7-EVT13) are left
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for periferical use.
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When installing an RTEMS interrupt handler RTEMS installs
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a generic Interrupt Handler which saves some context and
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enables nested interrupt servicing and then vectors
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to the users interrupt handler.
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@subsection Disabling of Interrupts by RTEMS
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During the execution of directive calls, critical
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sections of code may be executed. When these sections are
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encountered, RTEMS disables interrupts to level four (4) before
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the execution of this section and restores them to the previous
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level upon completion of the section. RTEMS uses the instructions
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CLI and STI to enable and disable Interrupts. Emulation,
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Reset, NMI and Exception Interrupts are never disabled.
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@subsection Interrupt Stack
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The Blackfin Architecuter works with two different kind of stacks,
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User and Supervisor Stack. Since RTEMS and its Application run
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in supervisor mode, all interrupts will use the interrupted
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tasks stack for execution.
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@section Default Fatal Error Processing
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the @code{rtems_fatal_error_occurred} directive when there is
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no user handler configured or the user handler returns control to
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RTEMS. The default fatal error handler performs the
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following actions:
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@itemize @bullet
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@item disables processor interrupts,
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@item places the error code in @b{r0}, and
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@item executes an infinite loop (@code{while(0);} to
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simulate a halt processor instruction.
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@end itemize
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@section Board Support Packages
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@subsection System Reset
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TBD
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@subsection Processor Initialization
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TBD
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