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PCI4451 Datasheet(PDF) 79 Page - Texas Instruments |
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PCI4451 Datasheet(HTML) 79 Page - Texas Instruments |
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79 / 216 page  4–11 4.19 CardBus Memory Limit Registers 0, 1 These registers indicate the upper address of a PCI memory address range. They are used by the PCI4451 to determine when to forward a memory transaction to the CardBus bus, and likewise, when to forward a CardBus cycle to PCI. Bits 31–12 of these registers are read/write and allow the memory base to be located anywhere in the 32-bit PCI memory space on 4-Kbyte boundaries. Bits 11–0 are read-only and always return 0s. Writes to these bits have no effect. Bits 8 and 9 of the bridge control register (offset 3Eh, see Section 4.24) specify whether memory windows 0 and 1 are prefetchable or nonprefetchable. The memory base register or the memory limit register must be nonzero in order for the PCI4451 to claim any memory transactions through CardBus memory windows (i.e., these windows are not enabled by default to pass the first 4K bytes of memory to CardBus). Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 Name Memory limit registers 0, 1 Type R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W Default 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Name Memory limit registers 0, 1 Type R/W R/W R/W R/W R R R R R R R R R R R R Default 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Register: Memory limit registers 0, 1 Type: Read-only, Read/Write Offset: 20h, 28h Default: 0000 0000h 4.20 CardBus I/O Base Registers 0, 1 These registers indicate the lower address of a PCI I/O address range. They are used by the PCI4451 to determine when to forward an I/O transaction to the CardBus bus, and likewise, when to forward a CardBus cycle to the PCI bus. The lower 16 bits of this register locate the bottom of the I/O window within a 64-Kbyte page, and the upper 16 bits (31–16) are all 0s which locate this 64-Kbyte page in the first page of the 32-bit PCI I/O address space. Bits 31–16 and bits 1–0 are read-only and always return 0s, forcing I/O windows to be aligned on a natural doubleword boundary in the first 64-Kbyte page of PCI I/O address space. These I/O windows are enabled when either the I/O base register or the I/O limit register is nonzero. The I/O windows are not enabled by default to pass the first doubleword of I/O to CardBus. Either the I/O base or the I/O limit register must be nonzero to enable any I/O transactions. Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 Name I/O base registers 0, 1 Type R R R R R R R R R R R R R R R R Default 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Name I/O base registers 0, 1 Type R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R R Default 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Register: I/O base registers 0, 1 Type: Read-only, Read/Write Offset: 2Ch, 34h Default: 0000 0000h |
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