34 lines
1.6 KiB
Plaintext
34 lines
1.6 KiB
Plaintext
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AST RESEARCH, INC. TECHNICAL BULLETIN #0744A 03-04-92
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=============================================================================
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AST 486 BASED SYSTEMS WITH ADAPTEC 1540 AND 1542B
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PROBLEM: AST 486 based systems using an Adaptec 1540 and 1542B SCSI HBA
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shows a significant loss of performance by Checkit and
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Sprinrite. Data transfer rates are reduced by 33 percent when
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compared to a Premium/386-33 or a Premium 386SX-16 system.
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CAUSE: Adaptec's controller request for the bus are being held off
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while the 486 completes code fetch sequences from Adaptec's
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byte-wide BIOS ROM. This results in 16 accesses to the ROM
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over the bus, because the 486 processor fetches 128 bits at a
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time then releases the bus. The 386 processor fetches 32 bits
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then releases the bus. Since the 486 processor holds Adaptec
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controller off the bus longer during this access, the overall
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performance is significantly reduced as compared to the 386
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based system.
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AFFECTED
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SYSTEMS: AST 486 based systems
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SOLUTION: It has been determined that this problem will not be fixed.
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Customers experiencing this problem should use QEMM-386
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version 5.1 or equivalent as a workaround. This application
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will allow shadowing of the Adaptec BIOS which will resolve
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the problem.
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