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diff --git a/cpu_supplement/sparc.rst b/cpu_supplement/sparc.rst new file mode 100644 index 0000000..a69beb2 --- /dev/null +++ b/cpu_supplement/sparc.rst @@ -0,0 +1,938 @@ +SPARC 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 SPARC architecture dependencies in this +port of RTEMS. This architectural port is for SPARC Version 7 and +8. Implementations for SPARC V9 are in the sparc64 target. + +It is highly recommended that the SPARC RTEMS +application developer obtain and become familiar with the +documentation for the processor being used as well as the +specification for the revision of the SPARC architecture which +corresponds to that processor. + +**SPARC Architecture Documents** + +For information on the SPARC architecture, refer to +the following documents available from SPARC International, Inc. +(http://www.sparc.com): + +- SPARC Standard Version 7. + +- SPARC Standard Version 8. + +**ERC32 Specific Information** + +The European Space Agency’s ERC32 is a three chip +computing core implementing a SPARC V7 processor and associated +support circuitry for embedded space applications. The integer +and floating-point units (90C601E & 90C602E) are based on the +Cypress 7C601 and 7C602, with additional error-detection and +recovery functions. The memory controller (MEC) implements +system support functions such as address decoding, memory +interface, DMA interface, UARTs, timers, interrupt control, +write-protection, memory reconfiguration and error-detection. +The core is designed to work at 25MHz, but using space qualified +memories limits the system frequency to around 15 MHz, resulting +in a performance of 10 MIPS and 2 MFLOPS. + +Information on the ERC32 and a number of development +support tools, such as the SPARC Instruction Simulator (SIS), +are freely available on the Internet. The following documents +and SIS are available via anonymous ftp or pointing your web +browser at ftp://ftp.estec.esa.nl/pub/ws/wsd/erc32. + +- ERC32 System Design Document + +- MEC Device Specification + +Additionally, the SPARC RISC User’s Guide from Matra +MHS documents the functionality of the integer and floating +point units including the instruction set information. To +obtain this document as well as ERC32 components and VHDL models +contact: +.. code:: c + + Matra MHS SA + 3 Avenue du Centre, BP 309, + 78054 St-Quentin-en-Yvelines, + Cedex, France + VOICE: +31-1-30607087 + FAX: +31-1-30640693 + +Amar Guennon (amar.guennon@matramhs.fr) is familiar with the ERC32. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +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. + +CPU Model Feature Flags +----------------------- + +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 section 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/sparc/sparc.h based upon the particular CPU +model defined on the compilation command line. + +CPU Model Name +~~~~~~~~~~~~~~ + +The macro CPU_MODEL_NAME is a string which designates +the name of this CPU model. For example, for the European Space +Agency’s ERC32 SPARC model, this macro is set to the string +"erc32". + +Floating Point Unit +~~~~~~~~~~~~~~~~~~~ + +The macro SPARC_HAS_FPU is set to 1 to indicate that +this CPU model has a hardware floating point unit and 0 +otherwise. + +Bitscan Instruction +~~~~~~~~~~~~~~~~~~~ + +The macro SPARC_HAS_BITSCAN is set to 1 to indicate +that this CPU model has the bitscan instruction. For example, +this instruction is supported by the Fujitsu SPARClite family. + +Number of Register Windows +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The macro SPARC_NUMBER_OF_REGISTER_WINDOWS is set to +indicate the number of register window sets implemented by this +CPU model. The SPARC architecture allows a for a maximum of +thirty-two register window sets although most implementations +only include eight. + +Low Power Mode +~~~~~~~~~~~~~~ + +The macro SPARC_HAS_LOW_POWER_MODE is set to one to +indicate that this CPU model has a low power mode. If low power +is enabled, then there must be CPU model specific implementation +of the IDLE task in cpukit/score/cpu/sparc/cpu.c. The low +power mode IDLE task should be of the form: +.. code:: c + + while ( TRUE ) { + enter low power mode + } + +The code required to enter low power mode is CPU model specific. + +CPU Model Implementation Notes +------------------------------ + +The ERC32 is a custom SPARC V7 implementation based on the Cypress 601/602 +chipset. This CPU has a number of on-board peripherals and was developed by +the European Space Agency to target space applications. RTEMS currently +provides support for the following peripherals: + +- UART Channels A and B + +- General Purpose Timer + +- Real Time Clock + +- Watchdog Timer (so it can be disabled) + +- Control Register (so powerdown mode can be enabled) + +- Memory Control Register + +- Interrupt Control + +The General Purpose Timer and Real Time Clock Timer provided with the ERC32 +share the Timer Control Register. Because the Timer Control Register is write +only, we must mirror it in software and insure that writes to one timer do not +alter the current settings and status of the other timer. Routines are +provided in erc32.h which promote the view that the two timers are completely +independent. By exclusively using these routines to access the Timer Control +Register, the application can view the system as having a General Purpose +Timer Control Register and a Real Time Clock Timer Control Register +rather than the single shared value. + +The RTEMS Idle thread take advantage of the low power mode provided by the +ERC32. Low power mode is entered during idle loops and is enabled at +initialization time. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +Calling Conventions +=================== + +Each high-level language compiler generates subroutine entry and exit code +based upon a set of rules known as the application binary interface (ABI) +calling convention. These rules address the following issues: + +- register preservation and usage + +- parameter passing + +- call and return mechanism + +An ABI calling convention is of importance when interfacing to subroutines +written in another language either assembly or high-level. It determines also +the set of registers to be saved or restored during a context switch and +interrupt processing. + +The ABI relevant for RTEMS on SPARC is defined by SYSTEM V APPLICATION BINARY +INTERFACE, SPARC Processor Supplement, Third Edition. + +Programming Model +----------------- + +This section discusses the programming model for the +SPARC architecture. + +Non-Floating Point Registers +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The SPARC architecture defines thirty-two +non-floating point registers directly visible to the programmer. +These are divided into four sets: + +- input registers + +- local registers + +- output registers + +- global registers + +Each register is referred to by either two or three +names in the SPARC reference manuals. First, the registers are +referred to as r0 through r31 or with the alternate notation +r[0] through r[31]. Second, each register is a member of one of +the four sets listed above. Finally, some registers have an +architecturally defined role in the programming model which +provides an alternate name. The following table describes the +mapping between the 32 registers and the register sets: + +.. code:: c + + +-----------------+----------------+------------------+ + | Register Number | Register Names | Description | + +-----------------+----------------+------------------+ + | 0 - 7 | g0 - g7 | Global Registers | + +-----------------+----------------+------------------+ + | 8 - 15 | o0 - o7 | Output Registers | + +-----------------+----------------+------------------+ + | 16 - 23 | l0 - l7 | Local Registers | + +-----------------+----------------+------------------+ + | 24 - 31 | i0 - i7 | Input Registers | + +-----------------+----------------+------------------+ + +As mentioned above, some of the registers serve +defined roles in the programming model. The following table +describes the role of each of these registers: + +.. code:: c + + +---------------+----------------+----------------------+ + | Register Name | Alternate Name | Description | + +---------------+----------------+----------------------+ + | g0 | na | reads return 0 | + | | | writes are ignored | + +---------------+----------------+----------------------+ + | o6 | sp | stack pointer | + +---------------+----------------+----------------------+ + | i6 | fp | frame pointer | + +---------------+----------------+----------------------+ + | i7 | na | return address | + +---------------+----------------+----------------------+ + +The registers g2 through g4 are reserved for applications. GCC uses them as +volatile registers by default. So they are treated like volatile registers in +RTEMS as well. + +The register g6 is reserved for the operating system and contains the address +of the per-CPU control block of the current processor. This register is +initialized during system start and then remains unchanged. It is not +saved/restored by the context switch or interrupt processing code. + +The register g7 is reserved for the operating system and contains the thread +pointer used for thread-local storage (TLS) as mandated by the SPARC ABI. + +Floating Point Registers +~~~~~~~~~~~~~~~~~~~~~~~~ + +The SPARC V7 architecture includes thirty-two, +thirty-two bit registers. These registers may be viewed as +follows: + +- 32 single precision floating point or integer registers + (f0, f1, ... f31) + +- 16 double precision floating point registers (f0, f2, + f4, ... f30) + +- 8 extended precision floating point registers (f0, f4, + f8, ... f28) + +The floating point status register (FSR) specifies +the behavior of the floating point unit for rounding, contains +its condition codes, version specification, and trap information. + +According to the ABI all floating point registers and the floating point status +register (FSR) are volatile. Thus the floating point context of a thread is the +empty set. The rounding direction is a system global state and must not be +modified by threads. + +A queue of the floating point instructions which have +started execution but not yet completed is maintained. This +queue is needed to support the multiple cycle nature of floating +point operations and to aid floating point exception trap +handlers. Once a floating point exception has been encountered, +the queue is frozen until it is emptied by the trap handler. +The floating point queue is loaded by launching instructions. +It is emptied normally when the floating point completes all +outstanding instructions and by floating point exception +handlers with the store double floating point queue (stdfq) +instruction. + +Special Registers +~~~~~~~~~~~~~~~~~ + +The SPARC architecture includes two special registers +which are critical to the programming model: the Processor State +Register (psr) and the Window Invalid Mask (wim). The psr +contains the condition codes, processor interrupt level, trap +enable bit, supervisor mode and previous supervisor mode bits, +version information, floating point unit and coprocessor enable +bits, and the current window pointer (cwp). The cwp field of +the psr and wim register are used to manage the register windows +in the SPARC architecture. The register windows are discussed +in more detail below. + +Register Windows +---------------- + +The SPARC architecture includes the concept of +register windows. An overly simplistic way to think of these +windows is to imagine them as being an infinite supply of +"fresh" register sets available for each subroutine to use. In +reality, they are much more complicated. + +The save instruction is used to obtain a new register +window. This instruction decrements the current window pointer, +thus providing a new set of registers for use. This register +set includes eight fresh local registers for use exclusively by +this subroutine. When done with a register set, the restore +instruction increments the current window pointer and the +previous register set is once again available. + +The two primary issues complicating the use of +register windows are that (1) the set of register windows is +finite, and (2) some registers are shared between adjacent +registers windows. + +Because the set of register windows is finite, it is +possible to execute enough save instructions without +corresponding restore’s to consume all of the register windows. +This is easily accomplished in a high level language because +each subroutine typically performs a save instruction upon +entry. Thus having a subroutine call depth greater than the +number of register windows will result in a window overflow +condition. The window overflow condition generates a trap which +must be handled in software. The window overflow trap handler +is responsible for saving the contents of the oldest register +window on the program stack. + +Similarly, the subroutines will eventually complete +and begin to perform restore’s. If the restore results in the +need for a register window which has previously been written to +memory as part of an overflow, then a window underflow condition +results. Just like the window overflow, the window underflow +condition must be handled in software by a trap handler. The +window underflow trap handler is responsible for reloading the +contents of the register window requested by the restore +instruction from the program stack. + +The Window Invalid Mask (wim) and the Current Window +Pointer (cwp) field in the psr are used in conjunction to manage +the finite set of register windows and detect the window +overflow and underflow conditions. The cwp contains the index +of the register window currently in use. The save instruction +decrements the cwp modulo the number of register windows. +Similarly, the restore instruction increments the cwp modulo the +number of register windows. Each bit in the wim represents +represents whether a register window contains valid information. +The value of 0 indicates the register window is valid and 1 +indicates it is invalid. When a save instruction causes the cwp +to point to a register window which is marked as invalid, a +window overflow condition results. Conversely, the restore +instruction may result in a window underflow condition. + +Other than the assumption that a register window is +always available for trap (i.e. interrupt) handlers, the SPARC +architecture places no limits on the number of register windows +simultaneously marked as invalid (i.e. number of bits set in the +wim). However, RTEMS assumes that only one register window is +marked invalid at a time (i.e. only one bit set in the wim). +This makes the maximum possible number of register windows +available to the user while still meeting the requirement that +window overflow and underflow conditions can be detected. + +The window overflow and window underflow trap +handlers are a critical part of the run-time environment for a +SPARC application. The SPARC architectural specification allows +for the number of register windows to be any power of two less +than or equal to 32. The most common choice for SPARC +implementations appears to be 8 register windows. This results +in the cwp ranging in value from 0 to 7 on most implementations. + +The second complicating factor is the sharing of +registers between adjacent register windows. While each +register window has its own set of local registers, the input +and output registers are shared between adjacent windows. The +output registers for register window N are the same as the input +registers for register window ((N - 1) modulo RW) where RW is +the number of register windows. An alternative way to think of +this is to remember how parameters are passed to a subroutine on +the SPARC. The caller loads values into what are its output +registers. Then after the callee executes a save instruction, +those parameters are available in its input registers. This is +a very efficient way to pass parameters as no data is actually +moved by the save or restore instructions. + +Call and Return Mechanism +------------------------- + +The SPARC architecture supports a simple yet +effective call and return mechanism. A subroutine is invoked +via the call (call) instruction. This instruction places the +return address in the caller’s output register 7 (o7). After +the callee executes a save instruction, this value is available +in input register 7 (i7) until the corresponding restore +instruction is executed. + +The callee returns to the caller via a jmp to the +return address. There is a delay slot following this +instruction which is commonly used to execute a restore +instruction – if a register window was allocated by this +subroutine. + +It is important to note that the SPARC subroutine +call and return mechanism does not automatically save and +restore any registers. This is accomplished via the save and +restore instructions which manage the set of registers windows. + +In case a floating-point unit is supported, then floating-point return values +appear in the floating-point registers. Single-precision values occupy %f0; +double-precision values occupy %f0 and %f1. Otherwise, these are scratch +registers. Due to this the hardware and software floating-point ABIs are +incompatible. + +Calling Mechanism +----------------- + +All RTEMS directives are invoked using the regular +SPARC calling convention via the call instruction. + +Register Usage +-------------- + +As discussed above, the call instruction does not +automatically save any registers. The save and restore +instructions are used to allocate and deallocate register +windows. When a register window is allocated, the new set of +local registers are available for the exclusive use of the +subroutine which allocated this register set. + +Parameter Passing +----------------- + +RTEMS assumes that arguments are placed in the +caller’s output registers with the first argument in output +register 0 (o0), the second argument in output register 1 (o1), +and so forth. Until the callee executes a save instruction, the +parameters are still visible in the output registers. After the +callee executes a save instruction, the parameters are visible +in the corresponding input registers. The following pseudo-code +illustrates the typical sequence used to call a RTEMS directive +with three (3) arguments: +.. code:: c + + load third argument into o2 + load second argument into o1 + load first argument into o0 + invoke directive + +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. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +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. + +Flat Memory Model +----------------- + +The SPARC architecture 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, half-word (2-bytes), word (4 bytes), or doubleword +(8 bytes). Memory accesses within this address space are +performed in big endian fashion by the SPARC. Memory accesses +which are not properly aligned generate a "memory address not +aligned" trap (type number 7). The following table lists the +alignment requirements for a variety of data accesses: + +.. code:: c + + +--------------+-----------------------+ + | Data Type | Alignment Requirement | + +--------------+-----------------------+ + | byte | 1 | + | half-word | 2 | + | word | 4 | + | doubleword | 8 | + +--------------+-----------------------+ + +Doubleword load and store operations must use a pair +of registers as their source or destination. This pair of +registers must be an adjacent pair of registers with the first +of the pair being even numbered. For example, a valid +destination for a doubleword load might be input registers 0 and +1 (i0 and i1). The pair i1 and i2 would be invalid. \[NOTE: +Some assemblers for the SPARC do not generate an error if an odd +numbered register is specified as the beginning register of the +pair. In this case, the assembler assumes that what the +programmer meant was to use the even-odd pair which ends at the +specified register. This may or may not have been a correct +assumption.] + +RTEMS does not support any SPARC Memory Management +Units, therefore, virtual memory or segmentation systems +involving the SPARC are not supported. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +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 SPARC’s +interrupt response and control mechanisms as they pertain to +RTEMS. + +RTEMS and associated documentation uses the terms +interrupt and vector. In the SPARC architecture, these terms +correspond to traps and trap type, respectively. The terms will +be used interchangeably in this manual. + +Synchronous Versus Asynchronous Traps +------------------------------------- + +The SPARC architecture includes two classes of traps: +synchronous and asynchronous. Asynchronous traps occur when an +external event interrupts the processor. These traps are not +associated with any instruction executed by the processor and +logically occur between instructions. The instruction currently +in the execute stage of the processor is allowed to complete +although subsequent instructions are annulled. The return +address reported by the processor for asynchronous traps is the +pair of instructions following the current instruction. + +Synchronous traps are caused by the actions of an +instruction. The trap stimulus in this case either occurs +internally to the processor or is from an external signal that +was provoked by the instruction. These traps are taken +immediately and the instruction that caused the trap is aborted +before any state changes occur in the processor itself. The +return address reported by the processor for synchronous traps +is the instruction which caused the trap and the following +instruction. + +Vectoring of Interrupt Handler +------------------------------ + +Upon receipt of an interrupt the SPARC automatically +performs the following actions: + +- disables traps (sets the ET bit of the psr to 0), + +- the S bit of the psr is copied into the Previous + Supervisor Mode (PS) bit of the psr, + +- the cwp is decremented by one (modulo the number of + register windows) to activate a trap window, + +- the PC and nPC are loaded into local register 1 and 2 + (l0 and l1), + +- the trap type (tt) field of the Trap Base Register (TBR) + is set to the appropriate value, and + +- if the trap is not a reset, then the PC is written with + the contents of the TBR and the nPC is written with TBR + 4. If + the trap is a reset, then the PC is set to zero and the nPC is + set to 4. + +Trap processing on the SPARC has two features which +are noticeably different than interrupt processing on other +architectures. First, the value of psr register in effect +immediately before the trap occurred is not explicitly saved. +Instead only reversible alterations are made to it. Second, the +Processor Interrupt Level (pil) is not set to correspond to that +of the interrupt being processed. When a trap occurs, ALL +subsequent traps are disabled. In order to safely invoke a +subroutine during trap handling, traps must be enabled to allow +for the possibility of register window overflow and underflow +traps. + +If the interrupt handler was installed as an RTEMS +interrupt handler, then upon receipt of the interrupt, the +processor passes control to the RTEMS interrupt handler which +performs the following actions: + +- saves the state of the interrupted task on it’s stack, + +- insures that a register window is available for + subsequent traps, + +- if this is the outermost (i.e. non-nested) interrupt, + then the RTEMS interrupt handler switches from the current stack + to the interrupt stack, + +- enables traps, + +- invokes the vectors to a user interrupt service routine (ISR). + +Asynchronous interrupts are ignored while traps are +disabled. Synchronous traps which occur while traps are +disabled result in the CPU being forced into an error mode. + +A nested interrupt is processed similarly with the +exception that the current stack need not be switched to the +interrupt stack. + +Traps and Register Windows +-------------------------- + +One of the register windows must be reserved at all +times for trap processing. This is critical to the proper +operation of the trap mechanism in the SPARC architecture. It +is the responsibility of the trap handler to insure that there +is a register window available for a subsequent trap before +re-enabling traps. It is likely that any high level language +routines invoked by the trap handler (such as a user-provided +RTEMS interrupt handler) will allocate a new register window. +The save operation could result in a window overflow trap. This +trap cannot be correctly processed unless (1) traps are enabled +and (2) a register window is reserved for traps. Thus, the +RTEMS interrupt handler insures that a register window is +available for subsequent traps before enabling traps and +invoking the user’s interrupt handler. + +Interrupt Levels +---------------- + +Sixteen levels (0-15) of interrupt priorities are +supported by the SPARC architecture with level fifteen (15) +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. Level fifteen (15) is a non-maskable interrupt +(NMI), which makes it unsuitable for standard usage since it can +affect the real-time behaviour by interrupting critical sections +and spinlocks. Disabling traps stops also the NMI interrupt from +happening. It can however be used for power-down or other +critical events. + +Although RTEMS supports 256 interrupt levels, the +SPARC only supports sixteen. RTEMS interrupt levels 0 through +15 directly correspond to SPARC processor interrupt levels. All +other RTEMS interrupt levels are undefined and their behavior is +unpredictable. + +Many LEON SPARC v7/v8 systems features an extended interrupt controller +which adds an extra step of interrupt decoding to allow handling of +interrupt 16-31. When such an extended interrupt is generated the CPU +traps into a specific interrupt trap level 1-14 and software reads out from +the interrupt controller which extended interrupt source actually caused the +interrupt. + +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 fifteen (15) +before the execution of the section and restores them to the +previous level upon completion of the section. RTEMS has been +optimized to ensure that interrupts are disabled for less than +RTEMS_MAXIMUM_DISABLE_PERIOD microseconds on a RTEMS_MAXIMUM_DISABLE_PERIOD_MHZ +Mhz ERC32 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.] + +[NOTE: It is thought that the length of time at which +the processor interrupt level is elevated to fifteen by RTEMS is +not anywhere near as long as the length of time ALL traps are +disabled as part of the "flush all register windows" operation.] + +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. + +Interrupts are disabled or enabled by performing a system call +to the Operating System reserved software traps 9 +(SPARC_SWTRAP_IRQDIS) or 10 (SPARC_SWTRAP_IRQDIS). The trap is +generated by the software trap (Ticc) instruction or indirectly +by calling sparc_disable_interrupts() or sparc_enable_interrupts() +functions. Disabling interrupts return the previous interrupt level +(on trap entry) in register G1 and sets PSR.PIL to 15 to disable +all maskable interrupts. The interrupt level can be restored by +trapping into the enable interrupt handler with G1 containing the +new interrupt level. + +Interrupt Stack +--------------- + +The SPARC architecture does not provide for a +dedicated interrupt stack. Thus by default, trap handlers would +execute on the stack of the RTEMS task which they interrupted. +This artificially inflates the stack requirements for each task +since EVERY task stack would have to include enough space to +account for the worst case interrupt stack requirements in +addition to it’s own worst case usage. RTEMS addresses this +problem on the SPARC by providing a dedicated interrupt stack +managed by software. + +During system initialization, 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. As +part of processing a non-nested interrupt, RTEMS will switch to +the interrupt stack before invoking the installed handler. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +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. + +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. + +If the BSP has been configured with ``BSP_POWER_DOWN_AT_FATAL_HALT`` +set to true, the default handler will disable interrupts +and enter power down mode. If power down mode is not available, +it goes into an infinite loop to simulate a halt processor instruction. + +If ``BSP_POWER_DOWN_AT_FATAL_HALT`` is set to false, the default +handler will place the value ``1`` in register ``g1``, the +error source in register ``g2``, and the error code in register``g3``. It will then generate a system error which will +hand over control to the debugger, simulator, etc. + +Symmetric Multiprocessing +========================= + +SMP is supported. Available platforms are the Cobham Gaisler GR712RC and +GR740. + +Thread-Local Storage +==================== + +Thread-local storage is supported. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + +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 SPARC 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. + +System Reset +------------ + +An RTEMS based application is initiated or +re-initiated when the SPARC processor is reset. When the SPARC +is reset, the processor performs the following actions: + +- the enable trap (ET) of the psr is set to 0 to disable + traps, + +- the supervisor bit (S) of the psr is set to 1 to enter + supervisor mode, and + +- the PC is set 0 and the nPC is set to 4. + +The processor then begins to execute the code at +location 0. It is important to note that all fields in the psr +are not explicitly set by the above steps and all other +registers retain their value from the previous execution mode. +This is true even of the Trap Base Register (TBR) whose contents +reflect the last trap which occurred before the reset. + +Processor Initialization +------------------------ + +It is the responsibility of the application’s +initialization code to initialize the TBR and install trap +handlers for at least the register window overflow and register +window underflow conditions. Traps should be enabled before +invoking any subroutines to allow for register window +management. However, interrupts should be disabled by setting +the Processor Interrupt Level (pil) field of the psr to 15. +RTEMS installs it’s own Trap Table as part of initialization +which is initialized with the contents of the Trap Table in +place when the ``rtems_initialize_executive`` directive was invoked. +Upon completion of executive initialization, interrupts are +enabled. + +If this SPARC implementation supports on-chip caching +and this 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 C +Applications Users Manual for the reset code +which is executed before the call to``rtems_initialize_executive``, the SPARC version has the following +specific requirements: + +- Must leave the S bit of the status register set so that + the SPARC remains in the supervisor state. + +- Must set stack pointer (sp) such that a minimum stack + size of MINIMUM_STACK_SIZE bytes is provided for the``rtems_initialize_executive`` directive. + +- Must disable all external interrupts (i.e. set the pil + to 15). + +- Must enable traps so window overflow and underflow + conditions can be properly handled. + +- Must initialize the SPARC’s initial trap table with at + least trap handlers for register window overflow and register + window underflow. + +.. COMMENT: COPYRIGHT (c) 1988-2002. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + |