TMP92CF30
2009-06-12
92CF30-82
3.6.6
Considerations for Using More Than One Bus Master
In the TMP92CF30, the SDRAM controller and DMA controller may act as the bus
master apart from the CPU. Therefore, care must be exercised to enable each of these
functions to operate smoothly.
To facilitate explanation of DMA operation performed by each bus master, the DMA
transfer operation performed by the DMA controller is defined as “HDMA” and the SDRAM
auto refresh operation performed by the SDRAM controller as “ARDMA”.
The following explains various cases where two or more bus masters may operate at the
same time.
(1)
CPU
+
HDMA
The DMA controller performs DMA transfer (HDMA) after issuing a bus request to
the CPU and getting a bus acknowledgement. The DMA controller may be active while
the CPU is in HALT mode (IDLE2 mode only), in which case HDMA does not interfere
with the CPU operation. However, if HDMA is started while the CPU is active, the CPU
cannot execute instructions while HDMA is being performed.
Before activating the DMA controller, therefore, it is necessary to estimate the CPU
stop time (defined as “t
STOP
(HDMA)”) based on the transfer time, transfer start
interval, and number of channels to be used.
CPU bus stop rate
=
t
STOP
(HDMA)[s] / HDMA start interval
[s]
HDMA start interval
[s]
=
HDMA start interrupt period [s]
Note: The HDMA start interval depends on the period of the HDMA start interrupt source. However, it is also possible
to start HDMA by software.
t
STOP
(HDMA) [s]
=
(Source read time + Destination write time)
×
Transfer count
+
α
state/byte
Memory Type
Read / Write
Internal RAM
External SDRAM
16-bit bus
External SRAM
16-bit bus
External SRAM
8-bit bus
Read
1 / 4
(Note 1)
Burst 1 / 2
(Note 2)
1 word 6 / 2
(Note 2)
2 / 2
(Note 3)
2 / 1
(Note 3)
Write
1 / 4
Burst 1 / 2
(Note 2)
1 word 3 / 2
(Note 2)
2 / 2
(Note 3)
2 / 1
(Note 3)
Note 1: 2-1-1-1 access. Each consecutive address can be accessed in 1 state.
Note 2: The transfer speed varies depending on the combination of source and destination.
a) When the source or destination is internal RAM or internal I/O (SFR), burst access (6-1-1-1 access) is
possible. Only consecutive addresses on the same page can be accessed in 1 state. Additional 4
states are needed at the end of each burst access.
b) When the source or destination is other than internal RAM or internal I/O, 1-word access is used.
Note 3: In the case of 0 waits
state/byte
I/O Type
Read / Write
I
2
S NANDF USB SPI
Read
−
2 / 2
2 / 2
2 / 4
Write
2 / 4
2 / 2
2 / 2
2 / 4
Содержание TLCS-900/H1 Series
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