External Master Support (60x-Compatible Mode)
MSC8113 Reference Manual, Rev. 0
Freescale Semiconductor
12-83
The following examples show how the two mechanisms work.
12.5.1 Hierarchical Bus Interface Example
Assume that one of the SC140 cores initiates a system bus read cycle that addresses the DSI of
another MSC8113. The programmer cannot predict when the SC140 core can latch valid data
because the internal local bus of another MSC8113 may be occupied (by the DMA controller, for
example).
The wait solution (UPM). The external device (DSI of another MSC8113) asserts
PUPMWAIT
to the memory controller to indicate that data is not ready. The memory
controller synchronizes this signal because the wait signal is asynchronous. As a result of
the wait signal assertion, the UPM enters a freeze mode at the rising edge of
CLKOUT
upon
encountering the WAEN bit being set in the UPM word. The UPM stays in freeze mode
until
PUPMWAIT
is deasserted, and then continues executing from the next entry to the end
of the pattern (LAST bit is set).
The external termination solution (GPCM). The external device (DSI of another
MSC8113) asserts
PGTA
to the memory controller when it can sample data. Note that
PGTA
is also synchronized.
12.5.2 Slow Devices Example
When an SC140 core initiates a read cycle from a device with an access time that exceeds the
maximum allowed by the user programming model, there are two solutions:
The wait solution (UPM). The SC140 core generates a read access from the slow device.
The device in turn asserts the wait signal until the data is ready. The SC140 core samples
data only after the wait signal is deasserted.
The external termination solution (GPCM). The SC140 core generates a read access from
the slow device, which must generate the asynchronous
PGTA
when it is ready.
12.6 External Master Support (60x-Compatible Mode)
The memory controller supports internal and external 60x-compatible bus masters. Accesses
from the MSC8113 internal system bus master are internal while accesses from an external bus
master are considered external. External bus master support is available only if the BCR[EBM]
bit is set. For strict 60x-compatible mode the BCR[ETM] bit must be clear; For further details see
Section 4.2, SIU Programming Model. There are two types of external bus masters.
Strict 60x-compatible device using a 64-bit data bus, such as MPC603e, MPC604e,
MPC750.
MSC8113-type devices, such as an MPC8260, MSC8101, MSC8102 or another
MSC8113.
Содержание MSC8113
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