Computer system with a paged non-volatile memory

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FIELD OF THE INVENTION

The present invention relates to the field of computer systems. Specifically, the present invention relates to the field of computer system architectures incorporating a non-volatile form of basic operating system processing logic.

BACKGROUND OF THE INVENTION

Many prior art computer systems are typically configured at a minimum with a processor, a random access memory device, and a read only memory device. Some systems, such as a variety of calculators, may operate with only a processor and a read only memory device. Read only memory devices (ROM) provide a non-volatile form of memory that is not destroyed when power is removed from the computer system.

Prior an computer systems are typically bootstrapped (i.e. power up initialized) using the processing logic (i.e. firmware) stored within the read only memory device internal to the computer system. Since the read only memory device is non-volatile, the firmware within ROM is guaranteed to contain valid data or instructions; thus, the prior an computer system can be reliably bootstrapped using firmware within ROM. Many computer systems have successfully used this technique. One such system is the IBM Personal Computer (PC) developed by the IBM Corporation of Armonk, N.Y. Prior an versions of the IBM PC use read only memory devices for storage of firmware or a basic input/output system (BIOS) software program. The BIOS is an operating system that provides the lowest level of software control over the hardware and resources of the computer system. ROM storage may also be used for non-volatile retention of network configuration data or application specific data. ROM devices in the prior art include basic read only memory devices (ROM), programmable read only memory devices (PROM), and erasable programmable read only memory devices (EPROM). Battery-backed random access memory devices such as CMOS RAM devices may also be used for non-volatile retention of network configuration data or application specific data in a computer system.

Although ROM-based computer systems have been very successful in the prior art, a number of problems exist with the use of these devices in a computer system. Most computer systems have a finite address space in which each of the computer system resources must operate. These resources include ROM, random access memory (RAM), input/output devices, and possibly other processors. ROM devices with a BIOS contained therein are typically constrained to a specific address range within the addsess space available. In order to maintain compatibility with a particular computer architecture, designers and developers in the computer industry create products in reliance on a particular ROM address standard. For example, the IBM PC AT architecture mandates that the ROM BIOS and other firmware based applications are limited to a 128K address space at the top of the first megabyte of memory. With this architecture, however, the ROM BIOS cannot exceed 128K of ROM space. Within this ROM space, the BIOS must contain processing logic for initializing and controlling many of the hardware systems and resources of the computer system. With the increased functionality of modern computer systems, the complexity of hardware systems and resources increases as does the quantity of BIOS code required to support them. Also, because of new technologies and capabilities such as Extended Industry Standard Architecture (EISA) systems, flash memory and multi-language support for international operation of a computer system, it is becoming increasingly unfeasible to fit all desired BIOS features within the 128K boundary of the IBM PC AT architecture. Other varieties of computer systems typically have an established limit for the size of their BIOS. Even though the need for expanding the BIOS boundary is growing, the boundary cannot be arbitrarily modified without losing compatibility with established standards.

Thus, a means for expanding the useable BIOS memory space without violating established BIOS address boundary standards is needed.

SUMMARY OF THE INVENTION

The present invention is a computer system wherein a paging technique is used to expand the useable non-volatile memory capacity beyond a fixed address space limitation. The computer system of the preferred embodiment comprises a bus for communicating information, a processor coupled with the bus for processing information, a random access memory device coupled with the bus for storing information and instructions for the processor, an input device such as an alpha numeric input device or a cursor control device coupled to the bus for communicating information and command selections to the processor, a display device coupled to the bus for displaying information to a computer user, and a data storage device such as a magnetic disk and disk drive coupled with the bus for storing information and instructions. In addition, the computer system of the preferred embodiment includes a flash memory component coupled to the bus for storing non-volatile code and data. Devices other than flash memory may be used for storing nonvolatile code and data. Using the present invention, a paging technique expands the useable non-volatile memory capacity beyond a fixed address space limitation.

The flash memory device used in the preferred embodiment contains four separately erasable/programmable non-symmetrical blocks of memory. One of these four blocks may be electronically locked to prevent erasure or modification of its contents once it is installed. This configuration allows the processing logic of the computer system to update or modify any selected block of memory without affecting the contents of other blocks. One memory block contains a normal BIOS. The BIOS comprises processing logic instructions that are executed by the processor.

In the preferred embodiment, the BIOS is constrained to the upper 128K of the first Mbyte of the addressable memory space in the computer system. Because of computer system design constraints and compatibility, the BIOS may not occupy locations outside of the upper 128K region. In the present invention, the useful BIOS memory space is effectively increased while maintaining the 128K boundary of the upper 128K region. This enlargement of the useable BIOS space is realized using the paging technique of the present invention. In the preferred embodiment, the address space of the non-volatile memory device is logically separated into four distinct 64K byte pages of memory (Pages 1-4). Using the apparatus and techniques of the present invention, Page 1, Page 3 and Page 4 may be individually swapped into the address space occupied by the BIOS (the swappable page area). In the preferred embodiment, Page 2 is held static and thus is not used as a swap area.

Each of the swappable pages, Page 1, Page 3, and Page 4, contain processing logic called swapping logic used during the swapping or paging operation. The swapping logic operates in conjunction with paging hardware to effect the swapping of pages into the region occupied by the BIOS. The high order processor address lines are input by a page decoder. The page decoder is used to modify the address actually presented to the non-volatile memory device. A page register provides a means by which the processor may select a page in non-volatile memory.

In an alternative embodiment of the present invention, several different forms of configuration or identification information may be stored in a page of non-volatile memory. Configuration information in this form may include EISA configuration data, other bus protocol information or network information. Identification information may include an Ethernet address, system serial numbers, or software license numbers.

It is therefore an object of the present invention to provide a means for expanding the memory capacity for the BIOS while maintaining address space boundaries. It is a further object of the present invention to provide a means for paging a system BIOS in a computer system. It is a further object of the present invention to provide a means for selecting a particular page of BIOS memory. It is a further object of the present invention to provide a means for swapping pages of BIOS. It is a further object of the present invention to provide a means for using page-resident processing logic for controlling the page swapping operation. It is a further object of the present invention to provide a means for maintaining at least one static page. It is a further object of the present invention to provide a means for storing configuration or identification information. It is a further object of the present invention to provide a means for storing and retrieving EISA information in flash memory.

These and other objects of the present invention will become apparent as presented and described in the following detailed description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the computer system of the present invention.

FIG. 2 is an illustration of the pages of BIOS used in the preferred embodiment.

FIGS. 3a and 3b illustrate the paging hardware used in the present invention.

FIGS. 4-6 are flow charts of the paging processing logic of the present invention.

FIGS. 7a through 7d illustrate a memory map in various paging configurations.

FIG. 8 illustrates processing logic for updating a flash memory device with EISA configuration data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is a computer system wherein a paging technique is used to expand the useable non-volatile memory capacity beyond a fixed address space limitation. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention, however, it will be apparent to one of ordinary skill in the art that these specific details need not be used to practice the present invention. In other instances, well known structures, circuits, and interfaces have not been shown in detail in order not to unnecessarily obscure the present invention.

Referring to FIG. 1, a block diagram of the architecture of the computer system of the present invention is illustrated. The preferred embodiment of the present invention is implemented using an 80386 or 80486 microprocessor manufactured by the Assignee of the present invention. It will be apparent to those of ordinary skill in the art, however, that alternative processors and computer system architectures may be employed. In general, such computer systems as illustrated by FIG. 1 comprise a bus 100 for communicating information, a processor 101 coupled with the bus for processing information, a random access memory device 102 coupled with bus 100 for storing information and instructions for the processor 101, an input device 104 such as an alphanumeric input device or a cursor control device coupled to the bus 100 for communicating information and command selections to the processor 101, a display device 105 coupled to the bus 100 for displaying information to a computer user, and a data storage device such as a magnetic disk and disk drive coupled with the bus 100 for storing information and instructions.

In addition, the computer system of the preferred embodiment includes a read only memory component 103 coupled to the bus 100 for storing non-volatile code and data. In the preferred embodiment, read only memory device 103 is a flash memory component well known in the art.

Several types of non-volatile memory devices currently existing in the art may be reprogrammed without removing the device from a circuit board on which the device is installed. One class of reprogrammable nonvolatile memory devices is flash memory. Several different types of flash memory devices exist in the art. Using a dedicated set of electrical signals, the contents of flash memory may be erased and reprogrammed with new data. Many prior art flash memory devices only allow complete erasure and reprogramming of all memory locations of the device. Other flash memory devices, however, are partitioned into separately erasable and programmable blocks of memory in a single flash memory device. In the preferred embodiment of the present invention, such a partitioned flash memory device is used. In the preferred embodiment, two flash memory devices denoted 28F001BT are used. The 28F001BT flash memory devices are 1M bit memory devices manufactured by the Assignee of the present invention. It will be apparent to those skilled in the art that other forms of reprogrammable non-volatile memory devices may be used with the invention taught herein. One example of such a non-flash device is an electrically erasable programmable read only memory (EEPROM).

The flash memory device used in the preferred embodiment contains four separately erasable/programmable non-symmetrical blocks of memory. One of these four blocks may be electronically locked to prevent erasure or modification of its contents once it is installed. This configuration allows the processing logic of the computer system to update or modify any selected block of memory without affecting the contents of other blocks. The dynamic updating of a selected area of non-volatile memory is the subject of a co-pending patent application Ser. No. 07/695,952, filed May 6, 1991, and assigned to the Assignee of the present invention.

In the preferred embodiment, a basic input/output system (BIOS) is stored in flash memory 103. In addition, other system and application specific processing logic and data parameters may also be stored in flash memory 103. The following sections describe how the contents of flash memory 103 may be paged in a manner allowing the effective size of the flash memory 103 to increase without expanding accesses beyond a fixed address boundary. It will be apparent to those skilled in the art that the paged flash memory technique of the present invention may be used in a computer system using any type of non-volatile memory and is not limited to a system employing flash memory.

Referring to the preferred embodiment illustrated in FIG. 2, a paged BIOS memory map of the contents of flash memory 103 is depicted. In the preferred embodiment, the BIOS is constrained to the upper 128K of the first Mbyte of the addressable memory space in the computer system. This address space is identified by region 320 illustrated in FIG. 2. In the prior art, the 128K region 320 is used for storage of the BIOS. The upper region 301 is used for storage of the normal system BIOS while the lower region 302 is used for storage of other logic and data such as overflow BIOS code and/or data, video or other BIOS's, set-up code or data, and other information or logic.

In the present invention, the useful BIOS memory space is effectively increased while maintaining the 128K boundary of region 320. This enlargement of the useable BIOS space is realized using the paging technique of the present invention. In the preferred embodiment, the memory map illustrated in FIG. 2 is logically separated into four distinct 64K byte pages of memory. These pages are denoted Page 1 (301), Page 2 (302), Page 3 (303), and Page 4 (304). Using the apparatus and techniques of the present invention, Page 3 (303) and Page 4 (304) may be individually swapped into the address space occupied by Page 1 (301). In the preferred embodiment, Page 2 (302) is held static and thus is not used as a swap area.

It will be apparent to those skilled in the art that the 64K byte page size of the preferred embodiment may be implemented as a different page size in order to better accommodate an alternative embodiment. The techniques of the present invention, however, may still be used with a different page size. Similarly, the preferred embodiment defines two swappable pages, page 3 (303) and page 4 (304), outside of the 128K boundary of region 320. It will be apparent to those skilled in the art that additional pages may be defined using the techniques of the present invention in order to further enlarge the useable area of the BIOS.

Each of the swappable pages, Page 1 (301), Page 3 (303), and Page 4 (304), contain processing logic called swapping logic used during the swapping or paging operation. For example, the swapping logic for Page 1 (301) occupies a location in region 315. Similarly, each swappable page has swapping logic that resides in a fixed location relative to each page. The swapping logic operates in conjunction with paging hardware to effect the swapping of pages into the region occupied by Page 1 (301). The operation of the swapping logic is described below in relation to the flow charts of FIGS. 4 and 5. The paging hardware of the present invention is described next.

Referring now to FIG. 3a, a block diagram of the paging hardware of the present invention is illustrated. A portion of the interface between processor 101 and non-volatile memory or flash device 103 is an address presented to flash memory and/or decoder logic on address lines 210. The address signals thus presented define the location in flash memory 103 accessed by processor 101. For purposes of illustration, address lines 210 are shown separated into two components. The address signals on lines 211 comprise the low-order 16 bits of the address output by processor 101. Higher-order address signals are output on line 212. It will be apparent to those skilled in the art that the number of high order address signals presented on line 212 depends on the address width of processor 101. For purposes of illustration, only four address signals or bits are shown on line 212 in order to illustrate an access to the highest order location of flash memory 103.

The four address lines on line 212 in the preferred embodiment are input by a page decoder 217. Page decoder 217 is used to modify the address actually presented to flash memory 103 on address lines 219. A second input to page decoder 217 comes from a page register 214 on line 216. Page register 214 provides a means by which processor 101 may select a page in flash memory 103. Processor 101 selects a page by outputting a binary value on lines 215 that corresponds to the desired page. In the preferred embodiment, the output on line 215 to page register 214 is performed using an OUT instruction provided in the instruction set of processor 101. The use of an OUT instruction for loading an external register in this manner is well known in the art. Once page register 214 is loaded with a page number, this page number is provided to page decoder 217 on line 216.

Page decoder 217 manipulates the address actually presented to flash memory 103 on address lines 219 by first reading the high order processor address bits received on lines 212. If the value represented by the high order processor address bits on lines 212 defines a processor access to the swappable page area (i.e. address range F0000h through FFFFFh), page decoder 217 then reads the page number stored in page register 214. The page number is used to replace the value of the high order processor address actually output to flash memory 103 on address lines 219. In this manner, a processor access to the swappable page area can be redirected to a pre-determined page. If the value represented by the high order processor address bits on lines 212 defines a processor access to an area of flash memory other than the swappable page area, the page decoder 217 does not need to read the page register and the processor address is passed through unmodified to the flash memory device 103.

An example of the operation of page register 214 and page decoder 217 is illustrated in FIG. 3b. If a value corresponding to Page 1 is loaded in page register 214 by processor 101 and a processor address in the swappable page range F0000h through FFFFFh is presented by processor 101 on lines 211 and 212, high order processor address bits 16-19 output by processor 101 on lines 212 each take a binary value of 1, thereby defining an address range of F0000h through FFFFFh. Because processor 101 has accessed the swappable page area, page decoder 217 is enabled to read page register 214 for the value stored therein. In this example, page decoder 217 reads a value corresponding to Page 1 and replaces the high order processor address with the Page 1 value. Thus, a flash memory address in the range of F0000h through FFFFFh is presented to the flash memory 103. This address range (F0000h through FFFFFh) corresponds to Page 1 (301) illustrated in FIG. 2. Because Page 1 was already located in the swappable page address space, no other page needed to be swapped in. Thus, for the simple case of Page 1, the processor address was essentially passed through to flash memory 103, even though the page decoder 217 still performed the address modification. This case is illustrated in FIG. 7a.

In the preferred embodiment, Page 2 will never be loaded in page register 215, since this is a non-swappable page. Thus a processor access to the non-swappable address area (E0000h through EFFFFh) does not produce address modification by page decoder 217. This case is illustrated in FIG. 7b.

Referring now to the Page 3 example illustrated in FIG. 3b, page register 214 is loaded with a value corresponding to Page 3. A processor address in the swappable page range F0000h through FFFFFh is presented by processor 101 on lines 211 and 212. In this case, page decoder 217 reads the Page 3 value from page register 214 and replaces the high order processor address with the Page 3 value. This address modification results in a redirection of the processor address to a different address in flash memory 103 corresponding to the location of Page 3. In the example of FIG. 3b, the Page 3 value is 0Dh. This value redirects the Page 3 access to the flash memory address range D0000h through DFFFFh. It will be apparent to those skilled in the art that the processor memory access may be redirected to any area of flash memory 103. Other alternative embodiments may use a different Page 3 value and thereby redirect a Page 3 access to a different location in flash memory 103. The Page 3 case is illustrated in FIG. 7c.

In the Page 4 example shown in FIG. 3b, a Page 4 value of 0Ch is used to redirect a processor 101 access to the flash memory address range C0000h through CFFFFh. Again, the redirection to address range C0000h through CFFFFh is only provided by way of example. Note also that the processor 101 is aware only of loading the page register and accessing the swappable page area (F0000h through FFFFFh) in flash memory 103. The processor 101 is not aware of the redirection of the high order processor address. The Page 4 case is illustrated in FIG. 7d.

In the last two examples shown in FIG. 3b, processor 101 accesses a non-swappable page area (i.e. area 301 ) so the address is not modified. In the first of these examples, processor 101 presents an address in the range E0000h through EFFFFh on lines 210. Since such an address is not in the swappable page area; therefore, the value in page register 214 becomes irrelevant. In this case, the page decoder 217 simply passes the processor address through to the flash memory 103. Thus, the address in the range E0000h through EFFFFh is presented to flash memory on lines 219. Similarly, a processor address in the range 0 through DFFFFh is presented unmodified to the bus 100.

In this manner, addresses output by processor 101 on lines 211 and 212 may be modified and redirected to the selected page of flash memory 103. It will be apparent to those skilled in the art that FIGS. 3a and 3b describe a modification of only four high order processor address lines, however, additional high order address lines or bits may be included in the manipulation by page decoder 217 in order to provide access to additional pages of BIOS. It will also be apparent to those skilled in the art that the swappable page area address range (F0000h through FFFFFh) used in the preferred embodiment to trigger the swapping operation for the system BIOS may be implemented at any memory range. Thus, the paging hardware of the present invention is described.

Processing logic for controlling the paged non-volatile memory system of the present invention is also included. This processing logic falls into two distinct pans: 1) pan one code or page selection logic and 2) part two code or swapping logic. Part one code is the processing logic that determines the page number that should be swapped into the region corresponding to the swappable page area. The part two code of the page control processing logic is the code that performs the switch or swapping to the next page. Part one code may reside anywhere within the BIOS or a swappable page. Part two code is located in the physical address range corresponding to the upper 8K of each swappable page. For example, the part two swapping logic for Page 1 resides in region 315 as shown in FIG. 2. Similarly, the part two swapping logic for Page 3 resides in region 310. This upper 8K address range corresponds to a compatibility section for the IBM PC where there are fixed entry points to various software interrupts and other fixed data regions. Between the fixed entry points and data regions are gaps of available memory. The part two swapping logic is positioned in one of these gaps. The part two swapping logic is always positioned at the same fixed address relative to each page. Each swappable page must have part two swapping logic. It will be apparent to those skilled in the art that the swapping logic for other computer system architectures may be located at a different position within the swappable pages, but at the same fixed addresses relative to each page.

Page switching in the present invention is activated by executing part one page selection processing logic. In the preferred embodiment, part one processing logic is executed by code in another page or via the activation of a distinctive sequence of alpha-numeric keystrokes. A particular keystroke sequence may be associated with each page. In the preferred embodiment, for example, Page 1 contains a power-on self test (POST) program. Page 1 with POST code is automatically selected on power-up or system reset. Page 3 contains set-up processing logic and Page 4 contains the run-time BIOS logic. The set-up page of Page 3 may be selected from the POST processing logic upon the occurrence of a configurat