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TMP92CZ26A
92CZ26A-236
3.10.3 An Example of Calculating HDMA Transfer Time
The following shows an example of calculating the HDMA transfer time when SDRAM is used as
the transfer source.
1) Transfer from SDRAM to internal SRAM
Conditions:
System clock (f
SYS
) : 60 MHz
SDRAM read cycle : Full page (5-1-1-1), 16-bit data bus
16-bit data bus
SDRAM Auto Refresh interval : 936 states (15.6 μs)
Internal RAM write cycle : 1 state, 32-bit data bus
Number of bytes to transfer : 512 bytes
Calculation example:
Transfer time = (SDRAM read time + SRAM write time) × transfer count
+ (SDRAM burst start + stop time)
+ (Precharge time + Auto Refresh time) × Auto Refresh count
(a) Read/write time
(SDRAM read 1 state × 2 + Internal RAM write 1 state) × 512 bytes/4 bytes
= 384 states × 1/60 MHz
= 6.4 μs
(b) Burst start/stop time
Start (TRCD: 2CLK) 5 states + Stop 2 states
= 7states/60 MHz
= 0.117 μs
(c) Auto Refresh time
Based on the above (a), Auto Refresh occurs once or zero times in 384 states. It is
assumed that Auto Refresh occurs once here.
(Precharge (TRP: 2CLK) 2 states + AREF (TRC: 5CLK) 5 states) ×AREF once
= 7 states × 1/60 MHz
= 0.117 μs
Total transfer time = (a) + (b) + (c)
= 6.4 μs + 0.117 μs + 0.117 μs
= 6.634 μs