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USB to SD throughput with EZ-USB™ FX3S, EZ-USB™ SD3, or EZ-USB™ SD2 - KBA233245

USB to SD throughput with EZ-USB™ FX3S, EZ-USB™ SD3, or EZ-USB™ SD2 - KBA233245

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Version: *A

For each storage port, the theoretical data rate at which data will be transferred can be calculated as follows:
Data rate (MBps): SD_CLK frequency * data bus width/8

  • SD_CLK frequency: Frequency of output clock (storage port)
  • Data bus width: Storage port bus width

Table 1 shows the conditions required for maximum throughput.

Table 1    Requirements for maximum throughput

Sr no.

 Item

 Details

1

Device used for testing

FX3S

2

SD card

SanDisk SD1N5C4 eMMC 4.41

3

SD bus width

8 bits

4

MMC clock frequency

52 MHz (DDR mode)

5

Driver

Windows mass storage device


Table 2     USB - SD card performance

USB speed

Read (MBps)

Write (MBps)

USB 3.0

44.5

49.6

USB 2.0

30.2

24.1

The standard Windows mass storage driver uses tiny bursts (64 KB) for mass storage data transfers, and the performance obtained is limited by various protocol overheads.

For the performance of EZ-USB™ FX3S with RAID 1 firmware, see section 8 of AN89661.

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