Motorola USB08 - Manual (Page 183)

Universal USB Device Driver (USBIO)
Programming Interface
USB08 Evaluation Board Designer Reference Manual
MOTOROLA Universal USB Device Driver (USBIO) 183
Bulk or Interrupt Write Transfers
The write operation is used to transfer data from the host (PC) to the
USB device. The buffer is divided into data pieces (packets) of the
FIFO size of the endpoint. These packets are sent to the USB device.
If the last packet of the buffer is smaller than the FIFO size a smaller
data packet is transferred. If the size of the last packet of the buffer is
equal to the FIFO size this packet is sent. No additional zero packet
is sent automatically. To send a data packet with length zero, set the
buffer length to zero and use a NULL buffer pointer.
Bulk or Interrupt Read Transfers
The read operation is used to transfer data from the USB device to the
host (PC). The buffer is divided into data pieces (packets) of the FIFO
size of the endpoint. The buffer size should be a multiple of the FIFO
size. Otherwise the last transaction can cause a buffer overflow error.
Figure E-3. Layout of an Isochronous Transfer Buffer
USBIO_ISO_TRANSFER (
NumberOfPackets = N;
...
)
1. USBIO_ISO_PACKET
2. USBIO_ISO_PACKET
N. USBIO_ISO_PACKET
1. Data Packet
2. Data Packet
N. Data Packet
T
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Offset
Offset
Offset