TMP92CF30
2009-06-12
92CF30-83
Sample 1: Calculation example for CPU + HDMA
Conditions:
CPU operation speed (f
SYS
)
: 60 MHz
I
2
S sampling frequency
: 48 kHz (60 MHz/25/50 = 48 kHz)
I
2
S data transfer bit length
: 16 bits
DMAC channel 0 used to transfer 5 Kbytes from internal RAM to I
2
S
Calculation example:
DMAC source data read time:
Internal RAM data read time
= 1 state/4 bytes (However, the first 1 byte requires 2 states.)
DMAC destination write time:
I
2
S register write time = 2 states/4 bytes
Transfer count
To transfer 5 Kbytes of data in 4-byte units, the transfer count is calculated as
follows:
5 Kbytes/4 bytes = 1280 [times]
Since I
2
S generates an interrupt for every 64 bytes, the DMAC’s counter A is set to
16 (64 bytes/4 bytes = 16 times) and counter B is set to 80.
Note: Since an interrupt is generated 80 times, the first read to internal RAM (which requires 1 additional state) occurs
80 times, requiring additional 80 states in total. In addition, from bus REQ to bus ACK, an overhead time of 2
states is also needed for each interrupt request, requiring additional 160 states in total.
t
STOP
(HDMA) = (((1
+
2)
×
16)
×
80)
+
80
+
160) / f
SYS
[s] = 68 [
μ
s]
HDMA start interval [s] = 1 / I
2
S sampling frequency [Hz]
×
(64 / 16 )
=
83.33
[ms]
CPU bus stop rate = t
STOP
(HDMA) [s] / HDMA start interval [s]
=
68
[
μ
s] / 83.33 [ms] = 0.08 [
%
]
Содержание TLCS-900/H1 Series
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