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diff --git a/doc/cpu_supplement/m68k.t b/doc/cpu_supplement/m68k.t new file mode 100644 index 0000000000..d684328277 --- /dev/null +++ b/doc/cpu_supplement/m68k.t @@ -0,0 +1,773 @@ +@c +@c COPYRIGHT (c) 1988-2002. +@c On-Line Applications Research Corporation (OAR). +@c All rights reserved. +@c +@c $Id$ +@c + +@ifinfo +@end ifinfo +@chapter Motorola M68xxx and Coldfire Specific Information + +The Real Time Executive for Multiprocessor Systems (RTEMS) +is designed to be portable across multiple processor +architectures. However, the nature of real-time systems makes +it essential that the application designer understand certain +processor dependent implementation details. These processor +dependencies include calling convention, board support package +issues, interrupt processing, exact RTEMS memory requirements, +performance data, header files, and the assembly language +interface to the executive. + +This document discusses the Motorola MC68xxx +architecture dependencies in this port of RTEMS. The MC68xxx +family has a wide variety of CPU models within it. The part +numbers for these models are generally divided into MC680xx and +MC683xx. The MC680xx models are more general purpose processors +with no integrated peripherals. The MC683xx models, on the +other hand, are more specialized and have a variety of +peripherals on chip including sophisticated timers and serial +communications controllers. + +It is highly recommended that the Motorola MC68xxx +RTEMS application developer obtain and become familiar with the +documentation for the processor being used as well as the +documentation for the family as a whole. + +@subheading Architecture Documents + +For information on the Motorola MC68xxx architecture, +refer to the following documents available from Motorola +(@file{http//www.moto.com/}): + +@itemize @bullet +@item @cite{M68000 Family Reference, Motorola, FR68K/D}. +@end itemize + +@subheading MODEL SPECIFIC DOCUMENTS + +For information on specific processor models and +their associated coprocessors, refer to the following documents: + +@itemize @bullet +@item @cite{MC68020 User's Manual, Motorola, MC68020UM/AD}. + +@item @cite{MC68881/MC68882 Floating-Point Coprocessor User's +Manual, Motorola, MC68881UM/AD}. +@end itemize + +@c +@c COPYRIGHT (c) 1988-2002. +@c On-Line Applications Research Corporation (OAR). +@c All rights reserved. +@c +@c $Id$ +@c + +@section CPU Model Dependent Features + + +Microprocessors are generally classified into +families with a variety of CPU models or implementations within +that family. Within a processor family, there is a high level +of binary compatibility. This family may be based on either an +architectural specification or on maintaining compatibility with +a popular processor. Recent microprocessor families such as the +SPARC or PowerPC are based on an architectural specification +which is independent or any particular CPU model or +implementation. Older families such as the M68xxx and the iX86 +evolved as the manufacturer strived to produce higher +performance processor models which maintained binary +compatibility with older models. + +RTEMS takes advantage of the similarity of the +various models within a CPU family. Although the models do vary +in significant ways, the high level of compatibility makes it +possible to share the bulk of the CPU dependent executive code +across the entire family. Each processor family supported by +RTEMS has a list of features which vary between CPU models +within a family. For example, the most common model dependent +feature regardless of CPU family is the presence or absence of a +floating point unit or coprocessor. When defining the list of +features present on a particular CPU model, one simply notes +that floating point hardware is or is not present and defines a +single constant appropriately. Conditional compilation is +utilized to include the appropriate source code for this CPU +model's feature set. It is important to note that this means +that RTEMS is thus compiled using the appropriate feature set +and compilation flags optimal for this CPU model used. The +alternative would be to generate a binary which would execute on +all family members using only the features which were always +present. + +This chapter presents the set of features which vary +across SPARC implementations and are of importance to RTEMS. +The set of CPU model feature macros are defined in the file +cpukit/score/cpu/m68k/m68k.h based upon the particular CPU +model defined on the compilation command line. + +@subsection CPU Model Name + +The macro CPU_MODEL_NAME is a string which designates +the name of this CPU model. For example, for the MC68020 +processor, this macro is set to the string "mc68020". + +@subsection Floating Point Unit + +The macro M68K_HAS_FPU is set to 1 to indicate that +this CPU model has a hardware floating point unit and 0 +otherwise. It does not matter whether the hardware floating +point support is incorporated on-chip or is an external +coprocessor. + +@subsection BFFFO Instruction + +The macro M68K_HAS_BFFFO is set to 1 to indicate that +this CPU model has the bfffo instruction. + +@subsection Vector Base Register + +The macro M68K_HAS_VBR is set to 1 to indicate that +this CPU model has a vector base register (vbr). + +@subsection Separate Stacks + +The macro M68K_HAS_SEPARATE_STACKS is set to 1 to +indicate that this CPU model has separate interrupt, user, and +supervisor mode stacks. + +@subsection Pre-Indexing Address Mode + +The macro M68K_HAS_PREINDEXING is set to 1 to indicate that +this CPU model has the pre-indexing address mode. + +@subsection Extend Byte to Long Instruction + +The macro M68K_HAS_EXTB_L is set to 1 to indicate that this CPU model +has the extb.l instruction. This instruction is supposed to be available +in all models based on the cpu32 core as well as mc68020 and up models. +@c +@c COPYRIGHT (c) 1988-2002. +@c On-Line Applications Research Corporation (OAR). +@c All rights reserved. +@c +@c $Id$ +@c + +@section Calling Conventions + + +Each high-level language compiler generates +subroutine entry and exit code based upon a set of rules known +as the compiler's calling convention. These rules address the +following issues: + +@itemize @bullet +@item register preservation and usage +@item parameter passing +@item call and return mechanism +@end itemize + +A compiler's calling convention is of importance when +interfacing to subroutines written in another language either +assembly or high-level. Even when the high-level language and +target processor are the same, different compilers may use +different calling conventions. As a result, calling conventions +are both processor and compiler dependent. + +@subsection Processor Background + +The MC68xxx architecture supports a simple yet +effective call and return mechanism. A subroutine is invoked +via the branch to subroutine (bsr) or the jump to subroutine +(jsr) instructions. These instructions push the return address +on the current stack. The return from subroutine (rts) +instruction pops the return address off the current stack and +transfers control to that instruction. It is is important to +note that the MC68xxx call and return mechanism 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. + +@subsection Calling Mechanism + +All RTEMS directives are invoked using either a bsr +or jsr instruction and return to the user application via the +rts instruction. + +@subsection Register Usage + +As discussed above, the bsr and jsr instructions do +not automatically save any registers. RTEMS uses the registers +D0, D1, A0, and A1 as scratch registers. These registers are +not preserved by RTEMS directives therefore, the contents of +these registers should not be assumed upon return from any RTEMS +directive. + +@subsection Parameter Passing + +RTEMS assumes that arguments are placed on the +current stack before the directive is invoked via the bsr or jsr +instruction. The first argument is assumed to be closest to the +return address on the stack. This means that the first argument +of the C calling sequence is pushed last. The following +pseudo-code illustrates the typical sequence used to call a +RTEMS directive with three (3) arguments: + +@example +@group +push third argument +push second argument +push first argument +invoke directive +remove arguments from the stack +@end group +@end example + +The arguments to RTEMS are typically pushed onto the +stack using a move instruction with a pre-decremented stack +pointer as the destination. These arguments must be removed +from the stack after control is returned to the caller. This +removal is typically accomplished by adding the size of the +argument list in bytes to the current stack pointer. + +@subsection User-Provided Routines + +All user-provided routines invoked by RTEMS, such as +user extensions, device drivers, and MPCI routines, must also +adhere to these calling conventions. + +@c +@c COPYRIGHT (c) 1988-2002. +@c On-Line Applications Research Corporation (OAR). +@c All rights reserved. +@c +@c $Id$ +@c + +@section Memory Model + + +A processor may support any combination of memory +models ranging from pure physical addressing to complex demand +paged virtual memory systems. RTEMS supports a flat memory +model which ranges contiguously over the processor's allowable +address space. RTEMS does not support segmentation or virtual +memory of any kind. The appropriate memory model for RTEMS +provided by the targeted processor and related characteristics +of that model are described in this chapter. + +@subsection Flat Memory Model + +The MC68xxx family supports a flat 32-bit address +space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4 +gigabytes). Each address is represented by a 32-bit value and +is byte addressable. The address may be used to reference a +single byte, word (2-bytes), or long word (4 bytes). Memory +accesses within this address space are performed in big endian +fashion by the processors in this family. + +Some of the MC68xxx family members such as the +MC68020, MC68030, and MC68040 support virtual memory and +segmentation. The MC68020 requires external hardware support +such as the MC68851 Paged Memory Management Unit coprocessor +which is typically used to perform address translations for +these systems. RTEMS does not support virtual memory or +segmentation on any of the MC68xxx family members. + +@c +@c Interrupt Stack Frame Picture +@c +@c COPYRIGHT (c) 1988-2002. +@c On-Line Applications Research Corporation (OAR). +@c All rights reserved. +@c +@c $Id$ +@c + +@section Interrupt Processing + + +Different types of processors respond to the +occurrence of an interrupt in its own unique fashion. In +addition, each processor type provides a control mechanism to +allow for the proper handling of an interrupt. The processor +dependent response to the interrupt modifies the current +execution state and results in a change in the execution stream. +Most processors require that an interrupt handler utilize some +special control mechanisms to return to the normal processing +stream. Although RTEMS hides many of the processor dependent +details of interrupt processing, it is important to understand +how the RTEMS interrupt manager is mapped onto the processor's +unique architecture. Discussed in this chapter are the MC68xxx's +interrupt response and control mechanisms as they pertain to +RTEMS. + +@subsection Vectoring of an Interrupt Handler + +Depending on whether or not the particular CPU +supports a separate interrupt stack, the MC68xxx family has two +different interrupt handling models. + +@subsubsection Models Without Separate Interrupt Stacks + +Upon receipt of an interrupt the MC68xxx family +members without separate interrupt stacks automatically perform +the following actions: + +@itemize @bullet +@item To Be Written +@end itemize + +@subsubsection Models With Separate Interrupt Stacks + +Upon receipt of an interrupt the MC68xxx family +members with separate interrupt stacks automatically perform the +following actions: + +@itemize @bullet +@item saves the current status register (SR), + +@item clears the master/interrupt (M) bit of the SR to +indicate the switch from master state to interrupt state, + +@item sets the privilege mode to supervisor, + +@item suppresses tracing, + +@item sets the interrupt mask level equal to the level of the +interrupt being serviced, + +@item pushes an interrupt stack frame (ISF), which includes +the program counter (PC), the status register (SR), and the +format/exception vector offset (FVO) word, onto the supervisor +and interrupt stacks, + +@item switches the current stack to the interrupt stack and +vectors to an interrupt service routine (ISR). If the ISR was +installed with the interrupt_catch directive, then the RTEMS +interrupt handler will begin execution. The RTEMS interrupt +handler saves all registers which are not preserved according to +the calling conventions and invokes the application's ISR. +@end itemize + +A nested interrupt is processed similarly by these +CPU models with the exception that only a single ISF is placed +on the interrupt stack and the current stack need not be +switched. + +The FVO word in the Interrupt Stack Frame is examined +by RTEMS to determine when an outer most interrupt is being +exited. Since the FVO is used by RTEMS for this purpose, the +user application code MUST NOT modify this field. + +The following shows the Interrupt Stack Frame for +MC68xxx CPU models with separate interrupt stacks: + +@ifset use-ascii +@example +@group + +----------------------+ + | Status Register | 0x0 + +----------------------+ + | Program Counter High | 0x2 + +----------------------+ + | Program Counter Low | 0x4 + +----------------------+ + | Format/Vector Offset | 0x6 + +----------------------+ +@end group +@end example +@end ifset + +@ifset use-tex +@sp 1 +@tex +\centerline{\vbox{\offinterlineskip\halign{ +\strut\vrule#& +\hbox to 2.00in{\enskip\hfil#\hfil}& +\vrule#& +\hbox to 0.50in{\enskip\hfil#\hfil} +\cr +\multispan{3}\hrulefill\cr +& Status Register && 0x0\cr +\multispan{3}\hrulefill\cr +& Program Counter High && 0x2\cr +\multispan{3}\hrulefill\cr +& Program Counter Low && 0x4\cr +\multispan{3}\hrulefill\cr +& Format/Vector Offset && 0x6\cr +\multispan{3}\hrulefill\cr +}}\hfil} +@end tex +@end ifset + +@ifset use-html +@html +<CENTER> + <TABLE COLS=2 WIDTH="40%" BORDER=2> +<TR><TD ALIGN=center><STRONG>Status Register</STRONG></TD> + <TD ALIGN=center>0x0</TD></TR> +<TR><TD ALIGN=center><STRONG>Program Counter High</STRONG></TD> + <TD ALIGN=center>0x2</TD></TR> +<TR><TD ALIGN=center><STRONG>Program Counter Low</STRONG></TD> + <TD ALIGN=center>0x4</TD></TR> +<TR><TD ALIGN=center><STRONG>Format/Vector Offset</STRONG></TD> + <TD ALIGN=center>0x6</TD></TR> + </TABLE> +</CENTER> +@end html +@end ifset + +@subsection CPU Models Without VBR and RAM at 0 + +This is from a post by Zoltan Kocsi <zoltan@@bendor.com.au> and is +a nice trick in certain situations. In his words: + +I think somebody on this list asked about the interupt vector +handling w/o VBR and RAM at 0. The usual trick is +to initialise the vector table (except the first 2 two entries, of +course) to point to the same location BUT you also add the vector +number times 0x1000000 to them. That is, bits 31-24 contain the vector +number and 23-0 the address of the common handler. +Since the PC is 32 bit wide but the actual address bus is only 24, +the top byte will be in the PC but will be ignored when jumping +onto your routine. + +Then your common interrupt routine gets this info by loading the PC +into some register and based on that info, you can jump to a vector +in a vector table pointed by a virtual VBR: + +@example +// +// Real vector table at 0 +// + + .long initial_sp + .long initial_pc + .long myhandler+0x02000000 + .long myhandler+0x03000000 + .long myhandler+0x04000000 + ... + .long myhandler+0xff000000 + + +// +// This handler will jump to the interrupt routine of which +// the address is stored at VBR[ vector_no ] +// The registers and stackframe will be intact, the interrupt +// routine will see exactly what it would see if it was called +// directly from the HW vector table at 0. +// + + .comm VBR,4,2 // This defines the 'virtual' VBR + // From C: extern void *VBR; + +myhandler: // At entry, PC contains the full vector + move.l %d0,-(%sp) // Save d0 + move.l %a0,-(%sp) // Save a0 + lea 0(%pc),%a0 // Get the value of the PC + move.l %a0,%d0 // Copy it to a data reg, d0 is VV?????? + swap %d0 // Now d0 is ????VV?? + and.w #0xff00,%d0 // Now d0 is ????VV00 (1) + lsr.w #6,%d0 // Now d0.w contains the VBR table offset + move.l VBR,%a0 // Get the address from VBR to a0 + move.l (%a0,%d0.w),%a0 // Fetch the vector + move.l 4(%sp),%d0 // Restore d0 + move.l %a0,4(%sp) // Place target address to the stack + move.l (%sp)+,%a0 // Restore a0, target address is on TOS + ret // This will jump to the handler and + // restore the stack + +(1) If 'myhandler' is guaranteed to be in the first 64K, e.g. just + after the vector table then that insn is not needed. + +@end example + +There are probably shorter ways to do this, but it I believe is enough +to illustrate the trick. Optimisation is left as an exercise to the +reader :-) + + +@subsection Interrupt Levels + +Eight levels (0-7) of interrupt priorities are +supported by MC68xxx family members with level seven (7) being +the highest priority. Level zero (0) indicates that interrupts +are fully enabled. Interrupt requests for interrupts with +priorities less than or equal to the current interrupt mask +level are ignored. + +Although RTEMS supports 256 interrupt levels, the +MC68xxx family only supports eight. RTEMS interrupt levels 0 +through 7 directly correspond to MC68xxx interrupt levels. All +other RTEMS interrupt levels are undefined and their behavior is +unpredictable. + +@subsection Disabling of Interrupts by RTEMS + +During the execution of directive calls, critical +sections of code may be executed. When these sections are +encountered, RTEMS disables interrupts to level seven (7) before +the execution of this section and restores them to the previous +level upon completion of the section. RTEMS has been optimized +to insure that interrupts are disabled for less than +RTEMS_MAXIMUM_DISABLE_PERIOD microseconds on a +RTEMS_MAXIMUM_DISABLE_PERIOD_MHZ Mhz MC68020 with +zero wait states. These numbers will vary based the +number of wait states and processor speed present on the target board. +[NOTE: The maximum period with interrupts disabled is hand calculated. This +calculation was last performed for Release +RTEMS_RELEASE_FOR_MAXIMUM_DISABLE_PERIOD.] + +Non-maskable interrupts (NMI) cannot be disabled, and +ISRs which execute at this level MUST NEVER issue RTEMS system +calls. If a directive is invoked, unpredictable results may +occur due to the inability of RTEMS to protect its critical +sections. However, ISRs that make no system calls may safely +execute as non-maskable interrupts. + +@subsection Interrupt Stack + +RTEMS allocates the interrupt stack from the +Workspace Area. The amount of memory allocated for the +interrupt stack is determined by the interrupt_stack_size field +in the CPU Configuration Table. During the initialization +process, RTEMS will install its interrupt stack. + +The MC68xxx port of RTEMS supports a software managed +dedicated interrupt stack on those CPU models which do not +support a separate interrupt stack in hardware. + + +@c +@c COPYRIGHT (c) 1988-2002. +@c On-Line Applications Research Corporation (OAR). +@c All rights reserved. +@c +@c $Id$ +@c + +@section Default Fatal Error Processing + + +Upon detection of a fatal error by either the +application or RTEMS the fatal error manager is invoked. The +fatal error manager will invoke the user-supplied fatal error +handlers. If no user-supplied handlers are configured, the +RTEMS provided default fatal error handler is invoked. If the +user-supplied fatal error handlers return to the executive the +default fatal error handler is then invoked. This chapter +describes the precise operations of the default fatal error +handler. + +@subsection Default Fatal Error Handler Operations + +The default fatal error handler which is invoked by +the fatal_error_occurred directive when there is no user handler +configured or the user handler returns control to RTEMS. The +default fatal error handler disables processor interrupts to +level 7, places the error code in D0, and executes a stop +instruction to simulate a halt processor instruction. + +@c +@c COPYRIGHT (c) 1988-2002. +@c On-Line Applications Research Corporation (OAR). +@c All rights reserved. +@c +@c $Id$ +@c + +@section Board Support Packages + + +An RTEMS Board Support Package (BSP) must be designed +to support a particular processor and target board combination. +This chapter presents a discussion of MC68020 specific BSP +issues. For more information on developing a BSP, refer to the +chapter titled Board Support Packages in the RTEMS +Applications User's Guide. + +@subsection System Reset + +An RTEMS based application is initiated or +re-initiated when the MC68020 processor is reset. When the +MC68020 is reset, the processor performs the following actions: + +@itemize @bullet +@item The tracing bits of the status register are cleared to +disable tracing. + +@item The supervisor interrupt state is entered by setting the +supervisor (S) bit and clearing the master/interrupt (M) bit of +the status register. + +@item The interrupt mask of the status register is set to +level 7 to effectively disable all maskable interrupts. + +@item The vector base register (VBR) is set to zero. + +@item The cache control register (CACR) is set to zero to +disable and freeze the processor cache. + +@item The interrupt stack pointer (ISP) is set to the value +stored at vector 0 (bytes 0-3) of the exception vector table +(EVT). + +@item The program counter (PC) is set to the value stored at +vector 1 (bytes 4-7) of the EVT. + +@item The processor begins execution at the address stored in +the PC. +@end itemize + +@subsection Processor Initialization + +The address of the application's initialization code +should be stored in the first vector of the EVT which will allow +the immediate vectoring to the application code. If the +application requires that the VBR be some value besides zero, +then it should be set to the required value at this point. All +tasks share the same MC68020's VBR value. Because interrupts +are enabled automatically by RTEMS as part of the initialize +executive directive, the VBR MUST be set before this directive +is invoked to insure correct interrupt vectoring. If processor +caching is to be utilized, then it should be enabled during the +reset application initialization code. + +In addition to the requirements described in the +Board Support Packages chapter of the Applications User's +Manual for the reset code which is executed before the call to +initialize executive, the MC68020 version has the following +specific requirements: + +@itemize @bullet +@item Must leave the S bit of the status register set so that +the MC68020 remains in the supervisor state. + +@item Must set the M bit of the status register to remove the +MC68020 from the interrupt state. + +@item Must set the master stack pointer (MSP) such that a +minimum stack size of MINIMUM_STACK_SIZE bytes is provided for +the initialize executive directive. + +@item Must initialize the MC68020's vector table. +@end itemize + +Note that the BSP is not responsible for allocating +or installing the interrupt stack. RTEMS does this +automatically as part of initialization. If the BSP does not +install an interrupt stack and -- for whatever reason -- an +interrupt occurs before initialize_executive is invoked, then +the results are unpredictable. + +@c +@c COPYRIGHT (c) 1988-2002. +@c On-Line Applications Research Corporation (OAR). +@c All rights reserved. +@c +@c $Id$ +@c + +@section Processor Dependent Information Table + + +Any highly processor dependent information required +to describe a processor to RTEMS is provided in the CPU +Dependent Information Table. This table is not required for all +processors supported by RTEMS. This chapter describes the +contents, if any, for a particular processor type. + +@subsection CPU Dependent Information Table + +The MC68xxx version of the RTEMS CPU Dependent +Information Table contains the information required to interface +a Board Support Package and RTEMS on the MC68xxx. This +information is provided to allow RTEMS to interoperate +effectively with the BSP. The C structure definition is given +here: + +@example +@group +typedef struct @{ + void (*pretasking_hook)( void ); + void (*predriver_hook)( void ); + void (*postdriver_hook)( void ); + void (*idle_task)( void ); + boolean do_zero_of_workspace; + unsigned32 idle_task_stack_size; + unsigned32 interrupt_stack_size; + unsigned32 extra_mpci_receive_server_stack; + void * (*stack_allocate_hook)( unsigned32 ); + void (*stack_free_hook)( void* ); + /* end of fields required on all CPUs */ + + m68k_isr *interrupt_vector_table; +@} rtems_cpu_table; +@end group +@end example + +@table @code +@item pretasking_hook +is the address of the user provided routine which is invoked +once RTEMS APIs are initialized. This routine will be invoked +before any system tasks are created. Interrupts are disabled. +This field may be NULL to indicate that the hook is not utilized. + +@item predriver_hook +is the address of the user provided +routine that is invoked immediately before the +the device drivers and MPCI are initialized. RTEMS +initialization is complete but interrupts and tasking are disabled. +This field may be NULL to indicate that the hook is not utilized. + +@item postdriver_hook +is the address of the user provided +routine that is invoked immediately after the +the device drivers and MPCI are initialized. RTEMS +initialization is complete but interrupts and tasking are disabled. +This field may be NULL to indicate that the hook is not utilized. + +@item idle_task +is the address of the optional user +provided routine which is used as the system's IDLE task. If +this field is not NULL, then the RTEMS default IDLE task is not +used. This field may be NULL to indicate that the default IDLE +is to be used. + +@item do_zero_of_workspace +indicates whether RTEMS should +zero the Workspace as part of its initialization. If set to +TRUE, the Workspace is zeroed. Otherwise, it is not. + +@item idle_task_stack_size +is the size of the RTEMS idle task stack in bytes. +If this number is less than MINIMUM_STACK_SIZE, then the +idle task's stack will be MINIMUM_STACK_SIZE in byte. + +@item interrupt_stack_size +is the size of the RTEMS +allocated interrupt stack in bytes. This value must be at least +as large as MINIMUM_STACK_SIZE. + +@item extra_mpci_receive_server_stack +is the extra stack space allocated for the RTEMS MPCI receive server task +in bytes. The MPCI receive server may invoke nearly all directives and +may require extra stack space on some targets. + +@item stack_allocate_hook +is the address of the optional user provided routine which allocates +memory for task stacks. If this hook is not NULL, then a stack_free_hook +must be provided as well. + +@item stack_free_hook +is the address of the optional user provided routine which frees +memory for task stacks. If this hook is not NULL, then a stack_allocate_hook +must be provided as well. + +@item interrupt_vector_table +is the base address of the CPU's Exception Vector Table. + +@end table |