Topic M1SC_FEA from CPU FAQ base

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SU.HARDW.PC.CPU (2:5020/299) SU.HARDW.PC.CPU From : Aleksandr Konosevich 2:5004/9 Wed 27 Sep 95 15:25 Subj : M1sc (Cx5x86) subj - p. - pp p pp ... 8) pp : ------------------- PCR0 Bit Definition 0 RSTK_EN Return Stack Enable. If=1: the Return Stacks is enabled and RET instruction will speculatively execute the code following the associated CALL to improve performance. If=0: the Return Stack is not enabled and optimum performance will not be achived. 1 BTB_EN Branch Target Buffer Enable If=1: the Branch Target Buffer is enabled and branch prediction occurs. If=0: no branch prediction will occurs. 2 LOOP_EN Loop Enable If=1: the CPU will not flush the prfetch buffer if the destination of a jump is already present in the prefetch buffer. This eliminates the need for a read from the cache and thus improve performance. 3-6 Reserved 7 LSSER Load Store Serialize Enable (Reorder Disable) If=1: all memory reads and writes will occurs in execution order (load store serializing enabled, reordering disabled) If=0: memory reads and writes can be reordered for optimum performance (load store serializing disabled, reordering enabled). Memory accesses in the address range 640K to 1M always be issued in execution order. LSSER should be set to ensure that memory-mapped I/O devices operating outside of the address range 640K to 1M will operate corectly. ----------------------------- H p : ------------------------------ PMR Bit Definition 1-0 CLK [1-0] Core Clock/Bus Clock Ratio If=0h: ratio=1/1 If=1h: ratio=2/1 (default power-up for CLKMUL pin=0) If=2h: ratio=reserved If=3h: ratio=3/1 (default power-up for CLKMUL pin=1) At reset, the CLK [1-0] bits are initialized to 1h if CLKMUL=0, or to 3h if CLKMUL=1. After reset completed, CLK [1-0] bits may be set to 0h in order to obtain lower power consumption. The defaul power-up value must be restored when peak CPU performance if required. 2 HLF_CLK Half Speed Clock If=1: the CPU core operates at half the speed of the external bus clock regardless of the CLK [1-0] bits except during external bus transfers. When an external bus transfer occurs, the core clock frequency automatically increases in frequency for the duration of the transfer. When the transfer is complete, the core returns to half the frequency of the bus. Note : bit 2 cleared to zero at reset, bits 3-7 reserved. --------------------------- 8) With best wishes, Aleksandr --- * Origin: ! ! intel' ! 8[] (2:5004/9)

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