Abstract:
A system abstraction layer enables selection from among at least two different processor abstraction layer components. By allowing the selection from a plurality of compressed components, better system adaptability may be achieved. For example, updates may be provided so that it is not necessary to update the entire basic input/output system each time a component of the processor abstraction layer needs to be updated. In addition, a variety of different platforms may be supported by one basic input/output system having a plurality of selectable processor abstraction layer component images.

Description:
BACKGROUND 
   This invention relates generally to initializing processor-based systems. 
   Before the operating system is called, the basic input/output system (BIOS) is responsible for initializing and booting the processor-based system. Once the BIOS has completed its tasks, it transfers control to the operating system. 
   The BIOS may include at least three different levels. The lowest level may be the processor abstraction layer (PAL) that communicates with the hardware and, particularly, the processor. A middle layer is called the system abstraction layer (SAL). The SAL may attempt to correct correctable errors after they are detected and reported by the PAL. The uppermost layer, called the extensible firmware interface (EFI), communicates with the operating system and, in fact, launches the operating system. 
   In some processor-based systems, more than one PAL component may be provided. For example, in one implementation, two processor-specific components, which may be denominated PAL_A_SPECIFIC and PAL-B, may be provided. These two processor-specific components may typically be stored in system flash and may have a functionality akin to that normally handled by microcode. A third component called PAL_A_GENERIC is processor-independent and is the first component to execute in response to a restart event in some architectures. 
   The PAL_A_GENERIC component searches a firmware interface table (FIT) to locate a suitable onboard processor compatible with PAL_A_SPECIFIC and authenticates the component. The FIT, also stored in system flash, contains starting addresses and sizes for firmware components outside the protected boot block. The PAL_A_SPECIFIC authenticates the PAL-B component. The PAL_A_SPECIFIC then discovers the PAL-B through a FIT constructed by the original equipment manufacturer detailing, where in the system flash, PAL-B can be found. 
   After authentication, the PAL_A_SPECIFIC passes control to the original equipment manufacturer provided SAL-A component code. The control flow at this point can be recovery in the case of failed signature verification of the PAL-B or in the case of an incompatible PAL-B with respect to a particular processor stepping. 
   Only a single PAL-B component is supported because of flash memory space constraints. When it is desired to update the PAL-B in system flash with a newer version of PAL-B, the customer may use a so-called crisis recovery flow. The crisis recovery flow entails user intervention including flipping jumper switches and inserting a disk. 
   Thus, there is a need for a way that enables updating of PAL components without the need for user intervention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic depiction of the BIOS in accordance with one embodiment of the present invention; 
       FIG. 2  is a schematic depiction of a system in accordance with one embodiment of the present invention; and 
       FIG. 3  is a flow chart for a system abstraction layer component in accordance with one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , the basic input/output system (BIOS) may include a PAL_A_GENERIC  18 , a PAL_A_SPECIFIC  20 , a system abstraction layer-A (SAL-A)  22 , a system abstraction layer-B (SAL-B)  26 , and a catalog of compressed processor abstraction layer-B (PAL-B) images  24  in one embodiment. Thus, the overall BIOS may be broken into a boot block  14  that is fault tolerant and a non-boot block  16 . A catalog  24  of compressed PAL-B images may be stored in a file partition  12  in one embodiment. In one embodiment, the file system partition  12  may be an extensible firmware interface (EFI) partition. In another embodiment the catalog  24  may be stored in a flash-based directory. Other storage access arrangements may also be used including network or other extensible storage channels. 
   Referring to  FIG. 2 , a platform  42  may be any processor-based system including a server, desktop computer, a laptop computer, a portable computer, or a hand held device, to mention a few examples. The platform  42  may include a processor  44  coupled to an interface or bridge  46 . The bridge  46  may be coupled to the system memory  50 , in one embodiment. The interface  46  is also coupled to a bus  52 . The bus  52  may be coupled to another interface  54 , as well as an event storage  58 , and a basic input/output system (BIOS) storage  10 . The BIOS storage  10  may store the BIOS including the non-boot block  14  and the boot block  16 . In one embodiment the storage  10  may be a flash memory. 
   Finally, in some embodiments, a baseboard management controller (BMC)  60  may also be coupled to the bus  52 . The BMC  60  is a controller that may be responsible for facilitating automatic network connections with the platform  42 . The BMC  60  is effectively a processor or controller used for system management purposes. For example, the BMC  60  may be utilized to wake up a platform  42  through a local area network. The interface  54  may be coupled to a hard disk drive  36  that, in turn, may be coupled to an EFI partition  12 . 
   When a restart event is detected, the PAL_A_GENERIC firmware  18  receives the restart event and searches a firmware interface table (FIT) the storage  10  to locate a suitable onboard processor compatible with PAL_A_SPECIFIC  20 . When this processor is found, the PAL_A_SPECIFIC component is authenticated and control is passed to the PAL_A_SPECIFIC component  20 . The PAL_A_SPECIFIC component  20  immediately hands control over to an original equipment manufacturer system abstraction layer-A (SAL-A) component at SALE_ENTRY. SALE_ENTRY is a shared SAL-A entry point from code in PAL-A and PAL-B for reset, recovery, machine check and initialization. The SAL-A component may be prepared specifically by each original equipment manufacturer for its particular platform  42 . 
   Referring to  FIG. 3 , the SAL-A code initially performs basic memory initialization, as indicated in block  34 . Then the code performs a processor identification as indicated in block  36 . The code interrogates the catalog  24  of compressed PAL-B images and locates a feasible image for the particular system as indicated in block  38 . The PAL images may be stored in a directory on the storage  10  in one embodiment or may be stored in a file system partition  12 , such as an EFI partition, on a disk in another embodiment also shown in  FIG. 2 . The processor identifier, determined in block  36 , may be utilized to determine the most feasible image. 
   On successful discovery of a PAL-B image, the SAL-A code shadows the PAL-B and creates a shadow firmware interface table as indicated in block  40  in one embodiment. Shadowing is copying ROM-based code and data structures to random access memory, for example to increase performance and allow updates of ROM-based data structures by initialization firmware. In another embodiment, SAL-A may shadow PAL-B in memory and then may tell PAL-A where PAL-B is in memory (instead of using a shadow FIT). 
   The code then invokes an authentication service using the memory-based PAL-B image. If the PAL-B image is found in the shadow FIT as determined in diamond  34 , a check at diamond  36  determines whether the digital signature authenticates. If so, the code calls back to the PAL-B for a late self-test as indicated in block  84 . If either the signature does not authenticate or the PAL-B does not exist, the system goes into crisis recovery flow  86 . 
   Thus, instead of immediate PAL-B challenge by PAL_A_SPECIFIC, a late authentication of PAL-B allows system code, which includes the SAL-A, to germinate more system states. This permits access to a set of compressed PAL-B images. The platform firmware then can create a memory-based FIT and shadow the PAL-B into memory. The platform firmware may then invoke the authentication service. 
   Since PAL_A_SPECIFIC performs a signature verification, an error or malicious shadowing of the PAL-B by platform firmware will be detected because the signature check will fail at diamond  82 . As such, this late shadowing need not compromise security assertions. Also, since the PAL-B is needed for the late self-test, deferring the security check should not compromise the flow. 
   In some embodiments, the ability to have a plurality of available PAL-B components without requiring excessive flash capacity may be advantageous. Various PAL-B components may be compressed, stored and accessed as appropriate given the applicable processor type. The selection of the appropriate component may be done without user interaction in some embodiments. This ability to access a selectable PAL-B component without user intervention permits upgrading of platforms with newer processors and enables processor manufacturers to support various generations of processors simultaneously in some embodiments. This ability to support multiple generations may reduce the costs of service calls and bills of materials for a single processor model in that the PAL-B components can be compressed or stored on disk, allowing migration to a smaller system flash memory. 
   In some embodiments, an update to PAL-B may be implemented without a full BIOS rebuild. This avoids the need to have the user update the entire BIOS, not just the processor-specific PAL-B. 
   While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.