System information

9 Benchmarks and Verification
512 bytes. The endpoint descriptor of a transfer pipe defines the maximum packet
size (wMaxPacketSize) which is accepted by the particular endpoint. But the host
controller can use smaller data packets than the allowed maximum packet size for the
transfer.
Block Size of a data transfer defines the size of the data packet which is requested by the
initiator.
Figure 9.7 shows the read performance to the emulated CD-ROM device. The throughput
is measured with two different transfer packet size corresponding to the block size of the
transfer. In this process, the host computer copies 256 MB of data from the emulated CD-
ROM device to the hard disc of the host. As expected, the throughput allowing 512 bytes
data packets is remarkably higher than the one which permits a maximum packet size of
64 bytes for the data transfers.
Figure 9.7: Read throughput to the CHARM USB CD-ROM device corresponding to the
block size of the transfer. The color of the bars defines one of the USB packet
sizes of the device: USB 1.1 (64 B) or USB 2.0 (512 B).
9.3 USB Compliance Test
The Universal Serial Bus (USB) specification [104] defines the product design targets at the
level of mechanisms and interfaces. To enable measurement of compliance in real products,
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