Compaq 99875320-5 Manual De Usuario
Section 4. USB Communications
MAX_PACKET_SIZE PROPERTY
Property ID:
Property ID:
0x03
Property Type:
Byte
Length: 1
byte
Get Property:
Yes
Set Property:
Yes
Default Value:
8
Description:
The value is a byte that represents the devices maximum packet size for the
Interrupt In Endpoint. The value can be set in the range of 1 – 64 and has
units of bytes. The maximum packet size tells the host the maximum size of
the Interrupt In Endpoint packets. For example, if the maximum packet size is
set to 8, the device will send HID reports in multiple packets of 8 bytes each
or less for the last packet of the report. This property can be used to speed up
or slow down the time it takes to send card data to the host. Larger packet
sizes speed up communications and smaller packet sizes slow down
communications. The trade-off is that speeding up the card data transfer rate
increases the USB bus bandwidth used by the device, and slowing down the
card data transfer rate decreases the USB bus bandwidth used by the device.
The value of this property will be sent to the host when the host requests the
device’s USB endpoint descriptor.
Interrupt In Endpoint. The value can be set in the range of 1 – 64 and has
units of bytes. The maximum packet size tells the host the maximum size of
the Interrupt In Endpoint packets. For example, if the maximum packet size is
set to 8, the device will send HID reports in multiple packets of 8 bytes each
or less for the last packet of the report. This property can be used to speed up
or slow down the time it takes to send card data to the host. Larger packet
sizes speed up communications and smaller packet sizes slow down
communications. The trade-off is that speeding up the card data transfer rate
increases the USB bus bandwidth used by the device, and slowing down the
card data transfer rate decreases the USB bus bandwidth used by the device.
The value of this property will be sent to the host when the host requests the
device’s USB endpoint descriptor.
This property is stored in non-volatile memory, so it will persist when the unit
is power cycled. When this property is changed, the unit must be reset (see
Command Number 2) or power cycled to have these changes take effect.
is power cycled. When this property is changed, the unit must be reset (see
Command Number 2) or power cycled to have these changes take effect.
Example Set Max Packet Size property Request (Hex):
Cmd Num
Data Len
Prp ID
Prp Value
01 02
03
08
Example Set Max Packet Size property Response (Hex):
Result Code Data Len
Data
00 00
Example Get Max Packet Size property Request (Hex):
Cmd Num
Data Len
Prp ID
00 01
03
Example Get Max Packet Size property Response (Hex):
Result Code Data Len
Prp Value
00 01
08
19