VIC068A able assume system controller functions (also known slot funct
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System Controller Operations
VIC068A able assume system controller functions (also known slot functions) strapping SCON* signal Low. reliable operation, SCON* signal must remain asserted duration operation. system controller, VIC068A performs following functions: priority, round robin, single-level arbitration driving IACK* daisy-chain driving BGiOUT* daisy-chain (all four levels) driving SYSCLK output driving SYSRESET* output driving BCLR* VMEbus arbitration timeout timer
following VIC068A registers used system controller: Transfer Timeout Register (TTR), bits Arbiter/Requestor Control Register (ARCR), Error Group Interrupt Control Register (EGICR),
1.4.1
VMEbus Arbitration
arbitration scheme programmed writing ARCR[7]. (priority) mode, BR3* highest priority BR0* lowest. Higher priority requests will handled before lower priority requests when mode. (round robin) scheme, arbitration priority assigned rotating basis. When granted requester request line BR[n]*, then highest priority next arbitration assigned request line BR[n-1]* BR3* previous level BR0*). Single-level arbitration obtained programming VIC068A setting requestors same level. When VIC068A system controller, senses state BRi* inputs. four BGiOUT* signals asserted, corresponding highest pending request level during that arbitration cycle. VIC068A, system controller, BRi* pending along with another potential master same request level, VIC068A does assert BGiOUT* itself.
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System Controller Operations
arbitration cycle begins with deassertion BBSY* signal. VIC068A waits minimum after deassertion BBSY* before asserting BGiOUT* signal. VIC068A deasserts BGiOUT* signal when BBSY* again reasserted. VIC068A asserts BCLR* signal part arbiter function when senses request higher priority than level current VMEbus master. This occur when VIC068A enabled both arbitration schemes. either case, VIC068A deasserts BCLR* when BBSY* deasserted. systems containing many contending VMEbus masters, arbitration fair requests strongly recommended prevent excessive latency some VMEbus masters. allocate unequal share bandwidth particular master, assign that master level shared with fewer masters.
1.4.2
VMEbus Arbitration Timeout Timer
After VIC068A asserted BGiOUT* signal, VIC068A system controller monitors long grant active. Failure assert BBSY* within causes VIC068A issue BBSY* VMEbus-required EGICR used generate interrupt VMEbus arbitration timeout condition. This timeout feature disabled. section 1.9.5.
1.4.3
VMEbus Transfer Timeout Timer
VIC068A contains VMEbus transfer timeout timer. When VIC068A configured system controller, transfer timeout timer enabled, VIC068A starts this timer assertion DSi*. timer expires before assertion DTACK* BERR*, BERR* asserted system controller. BERR* remains asserted until DSi*s removed. timer configured TTR[7:5]. BESR[4] when this timeout condition occurs.
1.4.4
Daisy-Chain Driver
VIC068A, system controller, drives BGiOUT* daisy-chain response VMEbus requests. When VIC068A system controller, BGiIN* lines inactive, need pulled High externally VIC068A (4.7-10K).
1.4.5
IACK* Daisy-Chain Driver
VIC068A, system controller, first device drive IACK* daisy chain (Figure 1-5). When VIC068A performing duties system controller, IACK* input internally tied IACKIN* input. When VMEbus interrupt handler drives IACK*
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System Controller Operations
VMEbus, system controller VIC068A will this IACK* input will react just like VIC068A located elsewhere VMEbus would when IACKIN* driven Low. section 1.9.2.
IACK* Daisy-Chain system controlslot IACKIN* IACKOUT* IACK* VIC068A slot IACKIN* IACKIACK* VIC068A slot IACKIN* IACKOUT* IACK* VIC068A
IACKIN* IACKIACK* VIC068A
logically tied together internally
Figure 1-5. IACK* Daisy-Chain
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