TOSHIBA
TMPR3904F Rev. 2.0
49
HPSREQ (High Priority Snoop Request)
HPGREQ (High Priority General Request)
SREQ (Snoop Request)
GREQ (General Request)
Which bus ownership of these should be used is to be set up in the POBus
field of the CConR of the EBIF.
These four vary in priority and functions.
The priority is, in order from the highest, HPSREQ, HPGREQ, SREQ, and
GREQ. Of these, the TX3904 built-in DMAC has only SREQ and GREQ.
Because the external bus master is daisy-chain connected in the downstream
of the built-in DMAC, if SREQ or GREQ is used, the priority is lower than the
built-in DMAC. If HPSREQ or HPGREQ is used, the priority is definitely higher
than the built-in DMAC.
In the case of different priority due to the different kinds of bus ownership, if
the bus master with higher priority requests the bus ownership when another
bus master with lower priority has the bus ownership, a forceful transit of the
bus master occurs through the BUSREL*. In the case of different priority by
the daisy-chain connection (when the bus ownership is the same), a forceful
transit of the bus master does not occur; and the bus master with higher
priority (in upstream) cannot be granted the bus ownership until the bus
master with lower priority (in downstream) has no more use of the bus
ownership to release it.
The difference in the function is whether or not there is a snoop function
request. With HPSREQ and SREQ, the snoop function of the TX39 Processor
Core works. With HPGREQ and GREQ, the snoop function does not work.
The snoop function is explained in the next section.
7.5.4
Snoop function
The TX39 Processor Core has a snoop function. It is a function to maintain
consistency between the data cache of the TX39 Processor Core and the data
of an external memory.
When the snoop function of the TX39 Processor Core works, the TX39
Processor Core watches the bus operation of the bus master; and when the
address in the write operation matches the address inside the data cache, it
makes the corresponding data inside the data cache invalid. By doing so, it
prevents the contents being different from the data cache when the contents of
the external memory are rewritten by the bus master.
The TX3904 built-in DMAC and the external bus master can select whether or
not to use the snoop function of the TX39 Processor Core.
If the snoop function is used, the consistency between the data cache and the
data in the external memory can be maintained. In this case, when the bus
master has a bus ownership, the pipeline shall be stalled if the TX39 Processor
Core tries to access the data cache or when an instruction cache miss occurs.
If the snoop function is not used, the consistency between the data cache and
the data in the external memory cannot be guaranteed. The TX39 processor
core issues the bus ownership release request then refills the cache memory.
However, when the bus master does not reply to that request, the pipeline
shall be stalled because the TX39 Processor Core cannot execute the bus
operation.
Summary of Contents for TMPR3904F
Page 1: ...Users Manual 32bit RISC Microprocessor TX39 family TMPR3904F Rev 2 0 Jan 12 1998 ...
Page 2: ......
Page 9: ...Users Manual 01 1 INTRODUCTION 1 1 Overview ...
Page 11: ...Users Manual 03 1 3 Kind of accessing by the TX3904 ...
Page 12: ...Users Manual 04 1 4 Precautions in the TMPR3904F specification Don t set Don t use ...
Page 13: ...Users Manual 05 Do not use ...
Page 14: ...Users Manual 06 ...
Page 15: ...Users Manual 7 2 FEATURES n n n n n n n n n n n n n ...
Page 16: ...Users Manual 8 ...
Page 18: ...Users Manual 10 ...
Page 19: ...Users Manual 11 4 PINS 4 1 Positions of Pins ...
Page 20: ...Users Manual 12 ...
Page 21: ...Users Manual 13 4 2 Functions of Pins ...
Page 22: ...Users Manual 14 ...
Page 23: ...Users Manual 15 ...
Page 24: ...Users Manual 16 ...
Page 26: ...Users Manual 18 5 2 Register Map ...
Page 27: ...Users Manual 19 ...
Page 28: ...Users Manual 20 ...
Page 30: ...Users Manual 22 5 3 2 PIO2 and PIO1 ...
Page 32: ...Users Manual 24 5 3 4 Connection of external bus master 5 3 5 INT 7 0 active status clear ...
Page 33: ...Users Manual 25 5 3 6 INT 7 0 active status set up ...
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