Table 17-2. Endpoint Fifo Characteristics; Isochronous Endpoints - Sharp LH79524 User Manual

LH79524/LH79525 User's Guide

17.1.1.1 Isochronous Endpoints

For Isochronous Endpoints, the host generates IN tokens based on the polling interval.
The SoC responds to the IN token with data packet. The polling interval is set in the soft-
ware driver.
Most of the standard drivers generate single IN token per polling period. Some custom
drivers may attempt to execute more than one transfer per polling period. This will result
in an error. Thus, drivers must be written that do not attempt more than one transfer per
polling period.
17.1.2 FIFOs
Each data pipe endpoint has a FIFO to assemble USB serial data into parallel data to be
used by the DMA controller. The FIFOs and maximum packet size for each endpoint are
described in Table 17-2.
17.1.3 Serial Interface Engine (SIE)
The SIE handles the direct USB interface. The Serial Interface functions include:
• Decoding and encoding
• Cyclic redundancy check (CRC) generation and checking
• Bit stuffing
• Endpoint address decoding for USB packets
• Interface signals for an external USB Transceiver.
The Serial Interface incorporates differential USB transceivers implementing a
USB-standard Full Speed interface, allowing communication at up to 12 Mbits/s.
17.1.3.1 OUT_PKT_RDY Interrupt Operation for Endpoint 0
The USB Host, via the protocol layer, sends a zero-length packet to acknowledge receipt
of data during control transactions. The USB Controller acknowledges this packet, but
doesn't generate an OUT_PKT_RDY Interrupt. This reduces communication overhead.
Since the next packet from the USB Controller is a Setup Packet, communication will tran-
spire with no problems. However, if the driver is written to use the OUT_PKT_RDY Interrupt,
it will not function. Drivers must be written without the use of the OUT_PKT_RDY Interrupt.

Table 17-2. Endpoint FIFO Characteristics

ENDPOINT FIFO SIZE
EP0 32 Bytes
EP1 In 128 Bytes
EP1 Out 128 Bytes
EP2 In 1024 Bytes
EP2 Out 1024 Bytes
EP3 In 128 Bytes
Version 1.0
Universal Serial Bus Device
MAXIMUM PACKET
SIZE
32 Bytes
64 Bytes
64 Bytes
1024 Bytes
1024 Bytes
64 Bytes
17-3