The MPC8xx Core
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
3-13
3.6.3.6
Atomic Update Primitives
The lwarx and stwcx. instructions are atomic update primitives that set and clear memory reservations.
Reservation accesses made by the same processor are implemented by the LSU. The external bus interface
implements memory reservations as they relate to accesses made by external bus devices. Accesses made
by other internal devices to internal memories implement memory reservations as they relate to special
internal bus snoop logic.
When an lwarx instruction executes, the LSU issues a cycle to the data cache with a special attribute. For
external memory accesses, this attribute causes the external bus interface to set a memory reservation
during the address tenure. External logic must then snoop the external bus to determine if another device
breaks the memory reservation by accessing the same location. KR and CR signals are available to external
logic to signal loss of a reservation to the external bus interface. When an stwcx. instruction addresses
external memory and the external bus interface determines that the reservation was lost, it blocks the
external bus access and notifies the LSU.
The MPC885 supports the memory reservation mechanism in a hierarchical bus structure. For reservations
on internal memory, an lwarx causes on-chip snoop logic to latch the address. This logic notifies the LSU
of any internal master store access and resets the reservation. If a new lwarx instruction address tenure
executes successfully, it replaces any previous reservation address at the appropriate snoop logic.
However, executing an stwcx. instruction cancels the reservation unless an alignment exception is
detected.
Half Word
0x00
1
Aligned
0x00/halfword
0x01
2
Unaligned
0x01/byte
0x02/byte
0x02
1
Aligned
0x02/halfword
0x03
2
Unaligned
0x03/byte
0x04/byte
Word
0x00
1
Aligned
0x00/word
0x01
3
Unaligned
0x01/byte
0x02/halfword
0x05/byte
0x02
2
Unaligned
0x02/halfword
0x04/halfword
0x03
3
Unaligned
0x03/byte
0x04/halfword
0x06/byte
Table 3-2. Bus Cycles Needed for Single-Register Load/Store Accesses (continued)
Transfer Size
Transfer Address (Last Two Bits)
Number of Bus Cycles
Transfer Type
Address/Size
Содержание PowerQUICC MPC870
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Страница 780: ...SCC Ethernet Mode MPC885 PowerQUICC Family Reference Manual Rev 2 27 24 Freescale Semiconductor ...
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Страница 944: ...Parallel I O Ports MPC885 PowerQUICC Family Reference Manual Rev 2 34 26 Freescale Semiconductor ...
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Страница 1004: ...Buffer Descriptors and Connection Tables MPC885 PowerQUICC Family Reference Manual Rev 2 37 30 Freescale Semiconductor ...
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Страница 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Страница 1120: ...AAL2 Implementation MPC885 PowerQUICC Family Reference Manual Rev 2 44 30 Freescale Semiconductor ...
Страница 1162: ...Fast Ethernet Controller FEC MPC885 PowerQUICC Family Reference Manual Rev 2 45 40 Freescale Semiconductor ...
Страница 1172: ...SEC Lite Overview MPC885 PowerQUICC Family Reference Manual Rev 2 46 8 Freescale Semiconductor ...
Страница 1176: ...SEC Lite Address Map MPC885 PowerQUICC Family Reference Manual Rev 2 47 4 Freescale Semiconductor ...
Страница 1214: ...SEC Lite Execution Units MPC885 PowerQUICC Family Reference Manual Rev 2 48 38 Freescale Semiconductor ...
Страница 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
Страница 1313: ...MPC885 PowerQUICC Family Reference Manual Rev 2 Freescale Semiconductor B 1 Appendix B Serial Communications Performance TBD ...
Страница 1314: ...Serial Communications Performance MPC885 PowerQUICC Family Reference Manual Rev 2 B 2 Freescale Semiconductor ...
Страница 1320: ...Register Quick Reference Guide MPC885 PowerQUICC Family Reference Manual Rev 2 C 6 Freescale Semiconductor ...
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