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AM79C976 Datasheet(PDF) 48 Page - Advanced Micro Devices |
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AM79C976 Datasheet(HTML) 48 Page - Advanced Micro Devices |
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48 / 309 page  48 Am79C976 8/01/00 P R E L I M INARY )LJXUH 7DUJHW $ERUW RTABORT (PCI Status register, bit 12) will be set to indicate that the Am79C976 controller has received a target abort. In addition, SINT (CSR5, bit 11) will be set to 1. When SINT is set, INTA is asserted if the enable bit SINTE (CSR5, bit 10) is set to 1. This mechanism can be used to inform the driver of the system error. The host can read the PCI Status register to determine the exact cause of the interrupt. 0DVWHU,QLWLDWHG7HUPLQDWLRQ There are three scenarios besides normal completion of a transaction where the Am79C976 controller will terminate the cycles it produces on the PCI bus. 3UHHPSWLRQ'XULQJ 1RQ%XUVW7UDQVDFWLRQ When the Am79C976 controller performs multiple non- burst transactions, it keeps REQ asserted until the as- sertion of FRAME for the last transaction. When GNT is removed, the Am79C976 controller will finish the cur- rent transaction and then release the bus. If it is not the last transaction, REQ will remain asserted to regain bus ownership as soon as possible. See Figure 1818. 3UHHPSWLRQ'XULQJ%XUVW7UDQVDFWLRQ When the Am79C976 controller operates in burst mode, it only performs a single transaction per bus mastership period, where transaction is defined as one address phase and one or multiple data phases. The central arbiter can remove GNT at any time during the transaction. The Am79C976 controller will ignore the deassertion of GNT and continue with data transfers, as long as the PCI Latency Timer is not expired. When the Latency Timer is 0 and GNT is deasserted, the Am79C976 controller will finish the current data phase, deassert FRAME, finish the last data phase, and re- lease the bus. It will immediately assert REQ to regain bus ownership as soon as possible. When the preemption occurs after the counter has counted down to 0, the Am79C976 controller will finish the current data phase, deassert FRAME, finish the last data phase, and release the bus. Note that it is im- portant for the host to program the PCI Latency Timer according to the bus bandwidth requirement of the Am79C976 controller. The host can determine this bus bandwidth requirement by reading the PCI MAX_LAT and MIN_GNT registers. FRAME CLK AD IRDY TRDY C/BE DEVSEL REQ GNT PAR DEVSEL is sampled 2 34567 ADDR 0000 0111 PAR PAR DATA STOP 1 22929B19 |
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