Cypress Semiconductor SL811HS Bedienungsanleitung PDF herunterladen (Seite 26)

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SL811HS and SL811HST: Application Notes

and specifications contained in this document are subject to change without

notice.

Date: 07/26/01

Revision: 1.21

Page: 26

The short Data Packet occurs when the host does not know the transfer length of the USB

device during the IN transaction. This can cause a Bus Time-out or a Babble condition.

Program Sample 10: Short Data Packet

... // check PID IN ... // check PID IN

if (pid == PID_IN) if (pid == PID_IN)

rem = (BYTE)SL11Read(EP0Counter); rem = (BYTE)SL11Read(EP0Counter);

len len --= rLen; // rLen = actual read/write= rLen; // rLen = actual read/write

if (bLen && len > 0) if (bLen && len > 0)

{ {

SL11Write(EP0XferLen, (BYTE)(bLen)); SL11Write(EP0XferLen, (BYTE)(bLen));

SL11W SL11Write(EP0Address, addr); // data addressrite(EP0Address, addr); // data address

// Clear the Interrupt Status // Clear the Interrupt Status

SL11Write(IntStatus, 0xff); SL11Write(IntStatus, 0xff);

if (pid == PID_IN && rem == 0) // Check to arm if (pid == PID_IN && rem == 0) // Check to arm

SL11Write(EP0Control, (DATA0_RD)); SL11Write(EP0Control, (DATA0_RD));

}}

if (pid == PID_IN) if (pid == PID_IN)

{ {

SL11BufRead((short)((Cmd & 0x40) ? data0: data1), buf, rLen); SL11BufRead((short)((Cmd & 0x40) ? data0: data1), buf, rLen);

//Short packet detection //Short packet detection

if (rem > 0) // Remainder Packet if (rem > 0) // Remainder Packet

{ {

printf(" printf("\\nShort packet detection %xnShort packet detection %x\\n", rem);n", rem);

return len; // return Length return len; // return Length

} }

... ...

4.1.11 USB Device Detection

USB device attachment and the speed of the attached device can be determined by monitoring

the SL811HS Interrupt status register bits -5 and bit-7 (IntStatus =0x0d). When a full-speed

device is attached, both bits -5 and bit-7 will be set =’1’. If a low speed device is attached, then

bit- 5 = ‘1’ and bit- 7=0.

SL811HS detects HUB as a full-speed USB device. After Enumeration process, SL811HS

software is able to determine the devices attached downstream of the HUB.

4.1.12 Full/Low Speed Detect

The SL811HS is able to detect attachment of full or low speed devices by monitoring bit-5, bit-

6, and bit-7 of register 0x0d. The speed_detect () function detects full/low speed device

attachment to the USB port. Also, this function generates the SOF/EOP for low/full speed

within 1ms.

When the SL811H is connected to a hub, the software must perform the following to avoid a

babble problem. This software implementation is a requirement for our chip. The developer

must follow this code so they will not have a missing packet problem. Initialization is required

for the interrupt.

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