Extended QBus System
MSC8113 Reference Manual, Rev. 0
Freescale Semiconductor
9-11
The fetch unit transfers an attribute on the QBus to indicate whether a transaction is a block or
prefetch. An upper arbiter that is a slave on the QBus uses this attribute to prioritize the access.
During a block access (“miss and the following first step of prefetch) the priority is high. The
priority is high also during a prefetch which is a prefetch “hit”.
9.3.2 QBus Execution Order
The QBus is the bus that connects the extended core to the MSC8113 system. All SC140 core
accesses above the QBus base line and prefetch to the cache are transferred on the QBus. The
EQBS prioritizes transfers on the QBus. The control unit sub-block in the EQBS determines the
execution order on the QBus according to the following priorities in descending order:
P-bus access (not prefetch)
XA-bus read
XB-bus read
XA-bus write immediate or immediate with no freeze
XB-bus write immediate or immediate with no freeze
XA-bus write
XB-bus write
Prefetch
The addresses are serviced on the QBus according to their priority. However, for a write buffer
flush, the write buffer gets the highest priority within accesses of the same core cycle.
9.3.3 QBus Banks
The bus has a single master (EQBS) and multiple slaves that are divided into four banks. There
can be more than one slave on each bank, and the slaves are divided according to the address
space. Each of the four QBus banks, Banks 0–3, has its own base address and size. Bank 0 has the
highest priority. If an address matches more than one bank, it is directed to the bank with the
highest priority. Each bank has a chip-select (CS) and some predefined dedicated signals for
specific slaves. Each bank performs different functions, as follows:
Bank 0 contains the addresses of the DSP peripherals, PIC, ICache, and the EQBS
registers. The upper half of Bank 0 (which contains the ICache, EQBS, and PIC registers)
is defined to execute all writes as immediate. This ensures that system register updates are
not delayed in the write buffer.
Bank 1 can be used to put any slave or interface on the QBus. In the MSC8113 it is used
for M2 (shared) memory.
Bank 2 is not used.
Bank 3 (the default bank) contains the system interface to the system bus.
Содержание MSC8113
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Страница 300: ...MSC8113 Reference Manual Rev 0 9 40 Freescale Semiconductor Extended Core ...
Страница 304: ...MSC8113 Reference Manual Rev 0 10 4 Freescale Semiconductor MQBus and M2 Memory ...
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