US006138183A Ulllted States Patent [19] [11] Patent Number: 6,138,183 Tien et al. [45] Date of Patent: Oct. 24, 2000 [54] TRANSPARENT DIRECT MEMORY ACCESS 5,778,242 7/1998 Wang ...................................... .. 712/40 5,805,842 9/1998 Nagaraj et al . 710/126 Inventors: Paul Tien, Fremont; Cheng_Yeuan Sakai ..................................... .. Tsay, Pleasanton; Rsong-Hsiang_ Shiao, OTHER PUBLICATIONS Fremont, all of Calif. Implementing Legacy Audio On The PCI Bus, by Gary [73] Assignee: ESS Technolgoy Inc., Fremont, Calif. Solomon, Intel Corporation 1997. Primary Examiner—Glenn A. Auve [21] Appl- N05 09/074,656 Attorney, Agent, or Firm—Gray Cary et al. [22] Filed: May 6, 1998 [57] ABSTRACT [51] Int. Cl.7 .................................................... .. G06F 13/14 Atransparent direct memory access method Comprises emw [52] US. Cl. .............................. .. 710/22; 710/129; 703/23 lating an ISA-bus mapped direct memory access controller [58] Field of Search .............................. .. 710/22, 28, 126, (ISA-DMAC) With a PCI-bus mapped direct memory access 710/129, 240, 260, 261, 264, 128; 395/50044, controller (PCI-DMAC). The ISA-DMAC exists, but there 500.45, 500.46, 500.47; 703/26, 25, 24, may not actually be any resources mapped into the ISA-bus 23 space. Write snooping by the PCI-DMAC of a PCI-bus _ processor detects Whenever an attempt is made to Write the [56] References Clted ISA-DMAC, and copies the data Written into the ISA DMAC registers into a corresponding register of the PCI U'S' PATENT DOCUMENTS DMAC. The direct memory access operation commanded 5,506,997 4/1996 Maguire et al. ...................... .. 710/260 by the PCI-bus processor of the ISA-DMAC is performed by 5,619,703 4/1997 Omid et a1- ---- - 710/261 the PCI-DMAC in the PCI-bus resource space. When the 576217902 4/1997 Cases et a1~ 710/129 direct memory access operation is completed, the PCI 27664497 9/1997 Kardach et a1‘ ' 710/240 DMAC updates its registers and does a Write back to update 5’673’400 9/1997 Kenpy """""" " 710/129 the ISA-DMAC registers. The PCI-bus processor can then ,678,064 10/1997 Kullk et al. .... .. .. 710/28 dth PCI DMAC d. H f t t .fl ft 5,729,762 3/1998 Kardach et al. .. 710/22 I“ ‘,3 ' “C y, or S a us’ or ,1 egacy so ‘Yam 577407452 4/1998 Story et aL ____ __ 710/261 is running the ISA-DMAC Wlll respond With the appropriate 5,745,772 4/1998 Klein ...... .. 710/266 reglster Value 5,752,043 5/1998 Suzuki .. 710/264 5,765,024 6/1998 Riley ....................................... .. 710/22 6 Claims, 3 Drawing Sheets / 8O / 86 PCI-DMAC f 82 ; _____ _ _T. pcl-oMAc 84 ‘\ ' ---- ---\* register PCI 98 processor PCI resources / 94 \ 88 —'—_T ISAnon-existent resources: PCI-bus - ----------- -- J ISA-DMAC :_____1_7\ 9e "*92 ,\ ISA-bus 9Q ISA-DMAC register U.S. Patent 0a. 24, 2000 Sheet 3 of3 6,138,183 ow mm. .90@ 255.611+......1. 56?:.4-_....- mm 60 63805 6,138,183 1 2 TRANSPARENT DIRECT MEMORY ACCESS PC-audio is predicted to move from ISA-bus based prod ucts implementing the SOUNDBLASTER® standard to FIELD OF THE INVENTION PCI-bus based products that Will deliver enhanced levels of The present invention relates to digital electronic circuits, performance. Products that provide backWard compatibility and more particularly to personal computer PCI-bus direct for legacy applications, as Well as enhanced DIRECT memory access controllers that emulate ISA-bus direct SOUND® performance, are eXpected to have a commercial memory access controllers and that redirect ISA-bus advantage during this period of transition. resource access requests to PCI-bus resources. The present Legacy game compatibility Will need to be maintained as invention further relates to high performance PCI-bus based more audio equipment and their manufacturers move to use PC audio solutions With a common architecture for desktop, the PCI-bus. notebook, and add-in card computers. The present invention Microsoft DOS-based games are conventionally sup speci?cally relates to PCI-bus solutions that maintain DOS ported by at least tWo industry legacy-support protocols, and SOUNDBLASTER® compatibility Without requiring e.g., PC/PCI-bus, and distributed DMA (DDMA). HoWever an ISA-bus, a particular core logic chipset, or a system these do not offer complete hardWare game compatibility motherboard implementation. 15 that is independent of the PC/PCI-bus or DDMA support. DESCRIPTION OF THE PRIOR ART Market realities are such that softWare compatibility must be IBM-compatible personal computers almost universally maintained for all applications Written for SOUND BLASTER PRO®, Ad Lib, Microsoft WINDOWS Sound used the industry standard architecture (ISA) bus in combi nation With a motherboard. A great deal of softWare has been System, DIRECTSOUNDTM, and Microsoft ACTIVEX®. Written and sold in the industry that is at least, in part, The bandWidth and bus mastering capabilities required for dependent on the ISA-bus softWare interfaces and systems optimum support of softWare that has been Written to resources. The peripheral component interconnect (PCI) bus Microsoft DIRECTSOUND®, DIRECT3DSOUND®, and is noW rapidly becoming the universal standard amongst DIRECTX® application programming interfaces require a PCI-bus system. The market also demands that PC audio personal computer manufacturers and users. HoWever, the 25 softWare interfaces and systems resources on a PCI-bus solutions continue to support the vast installed base of system are different enough to make the installed base of applications developed for the SOUNDBLASTER/ISA-bus ISA-bus dependent softWare at least partially incompatible standard. Complete hardWare support is needed for eXisting and not upWard compatible. softWare titles Written for the SOUNDBLASTER standard A group of system-bus chip manufacturers have joined Without diminishing the neW audio capabilities enabled by forces to endorse a technology they say Will help vendors the PCI-bus. miX PCI and ISA bus subsystems or integrated circuits. Therefore, an advanced and scalable PCI-bus based audio HoWever, analysts describe the so-called Common Archi product family is needed that preserves complete DOS game tecture proposal as a neW solution to a problem already support, regardless of core logic legacy support, to eliminate adequately solved. The alliance members, Digital Equip 35 the competitive risk of not being compatible With the huge ment Corp., National Semiconductor Corp., Opti, Pico installed base of DOS games. PoWer Technology, Standard Microsystems Corp., TeXas As a baseline feature, the PC audio system has been Instruments, and VLSI Technology, say the proposed stan overlooked for years. While the graphics market has been dard Will improve the handling and implementation of ISA the recipient of broad and rapid innovation, the PC audio and PCI devices in a single computer. The neW proposal system has been neglected. All of this is about to change. As partitions the motherboard, alloWing system integrators the audio system makes the jump from ISA to PCI, it is greater ?exibility in their choices of components such as afforded access to a tremendous increase in bandWidth that core logic, PCI bridges, and graphics controllers. Because translates into a host of neW features and innovation. One integrators Will have more component options, its advocates neW feature, Wavetable synthesis, has really been around for say, Common Architecture should reduce overall manufac 45 several years. HoWever, most traditional Wavetable solutions turing costs. Devices based on Common Architecture Will Were implemented in an eXtra synthesis chip and required a emphasiZe the neWer PCI bus, With the older ISA bus Wavetable ROM to store sound samples. The latest PCI supported as an optional feature. While ISA legacy devices audio controller chips integrate the Wavetable synthesis onto Will be fully supported, physical-component connections an audio controller chip. With access to PCI’s bandWidth, Will be routed through the PCI bus to eliminate sideband sound samples can be stored in main memory and the signals that straddle the chip set. The PCI bus Will support Wavetable ROM can be eliminated. The net result is less cost distributed direct memory access (DMA) on the ISA side. for the audio subsystem. Manufacturers Will have the option of using sideband signals A major stumbling block to PCI-based audio is so-called and eXtra chips on either side. Analysts are nonplused, “legacy” audio compatibility. PC audio Was initially devel pointing out that system vendors seem satis?ed With current 55 oped in a DOS World, along With ISA interrupts and ISA PCI/ISA architectures, bus standards, and core-logic chip DMA requests. A large base of PC game developers incor sets. porated ISA hardWare-speci?c code in their softWare. As a The PCI-based audio and communications accelerator result, these games are married to SOUNDBLASTER— industry is also rapidly transitioning from ISA bus-based compatible legacy audio. Supporting such hardWare-speci?c audio solutions to the more poWerful PCI-bus enabled code has turned out to be a tremendous challenge for neW engines. The ISA-bus is increasingly unable to support the audio chips as they move to the ISA bus. HoWever, support advanced audio processing required by neW multimedia of the installed softWare base remains a baseline requirement applications and upcoming personal computer standards. for neW audio solutions. Despite such challenges, PCI-based This is driving the need for high bandWidth PCI-bus accel audio is here. erators. A second factor is the close coupling of audio and 65 According to Aureal Semiconductor (Fremont, Calif.) modem technology that makes integrating these subsystems DOS legacy compatibility is important, no PC audio solu more attractive. tion is complete Without support for DOS legacy applica 6,138,183 3 4 tions. The Aureal AU8820 provides DOS audio legacy FIG.