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CS5535-UDC Datasheet(PDF) 77 Page - National Semiconductor (TI) |
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CS5535-UDC Datasheet(HTML) 77 Page - National Semiconductor (TI) |
77 / 555 page Revision 0.8 77 www.national.com GLPCI_SB Functional Description (Continued) 4.2.1 GeodeLink Interface The GeodeLink Interface block provides a thin protocol conversion layer between the transaction forwarding mod- ule and the GLIU. It is responsible for multiplexing in-bound write request data with out-bound read response data on the single GLIU data out bus. 4.2.2 FIFOs/Synchronization The FIFO block consists of a collection of in-bound and out-bound FIFOs. Each FIFO provides simple, synchro- nous interfaces to the reader and to the writer. The FIFO block also includes synchronization logic for a few non-FIFO related signals and clock gating logic. 4.2.3 Transaction Forwarding The Transaction Forwarding block receives, processes, and forwards transaction requests and responses between the GeodeLink Interface and PCI Bus Interface blocks. It imple- ments the transaction ordering rules. It performs write/read prefetching as needed. It also performs the necessary translation between GLIU and PCI commands. The Trans- action Forwarding block also handles the conversion between 64-bit GLIU data paths and 32-bit PCI data paths. Out-bound transactions are handled in a strongly ordered fashion. All out-bound memory writes are posted. The SEND_RESPONSE flag is never expected to be set in a memory write and is ignored. Any queued out-bound requests are flushed prior to handling an in-bound read request. All in-bound memory writes are posted. South bridge mas- ter out-bound read request data can pass in-bound writes. Thus, a pending out-bound read request need not be deferred while posted in-bound write data is waiting to be flushed or is in the process of being flushed. The out-bound read request may be performed on the PCI bus at the same time that the in-bound write data is flowing through the GLIU. When handling an in-bound read request, the intended size of the transfer is unknown. In-bound read requests for non- prefetchable addresses will only fetch the data explicitly indicated in the PCI transaction. Thus, all in-bound read requests made to non-prefetchable addresses will return at most a single 32-bit WORD. In-bound read requests made to prefetchable memory may cause more than a 32-bit WORD to be prefetched. The amount of data prefetched is configurable via the read threshold fields of the Global Control (GLPCI_CTRL), MSR 51000010h. Multiple read requests may be generated to satisfy the read threshold value. In-bound read requests may pass posted in-bound write data when there is no address collision between the read request and the address range of the posted write data (dif- ferent cache lines) and the read address is marked as being prefetchable. Support IDE data port Read Prefetch when MSR Control register (MSR 51000010h[19:18]) is set to IDE prefetch for performance enhancement. I/O reads to address 1F0h can follow a prefetching behavior. When enabled, the GLPCI_SB issues GLIU Read Request Packets for this specific address before receiving a request on the PCI bus for it. All PCI accesses to 1F0h must be DWORDs; that is, 4 bytes. 4.2.4 PCI Bus Interface The PCI Bus Interface block provides a protocol conversion layer between the transaction forwarding module and the PCI bus. The master and target portions of this module operate independently. Thus, out-bound write requests and in-bound read responses are effectively multiplexed onto the PCI bus. It includes address decoding logic to recog- nize distinct address regions for slave operation. Each address region is defined by a starting address, an address mask, and some attached attributes (i.e., memory and/or I/O space indicator, prefetchable, retry/hold, postable mem- ory write, region enable). The PCIF is responsible for retrying out-bound requests when a slave termination without data is seen on the PCI bus. It also must restart transactions on the PCI that are prematurely ended with a slave termination. This module also always slave terminates in-bound read transactions issued to non-prefetchable regions after a single WORD has been transferred. 4.2.5 CPU Interface Serial The CPU Interface Serial block provides a serial interface to the CPU for side-band signals. From reset, the GLPCI_SB connects only the SUSP# signal to the serial output. All other signals must be added by programming the CIS mode (MSR 51000010h[4:3]). Any change of the signals selected from the 16 side-band signals will start shifting to the CPU all 20 bits of the CIS register including two START bits (00) and two padding STOP bits (11). Three different modes control the selection of the side- band signals to the CIS shift register. 4.2.6 Programmable ID Selection An ID select register, IDSEL[31:0], is used for programma- ble ID selection. Only one bit in IDSEL[31:12] is set and used as a chip select (i.e., compared with AD[31:12]) dur- ing a PCI configuration write/read. The reset value of the IDSEL register is 02000000h. After reset, the first 32-bit I/O write PCI command (i.e., BE# = 0h) with address 00000000h and one bit set in AD[31:0] is assumed to ini- tialize the IDSEL register. Only data with one bit set in AD[31:0] is considered valid. All other values are ignored and will not change the contents of IDSEL. |
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