UM0851 datasheet(78/245 Pages) STMICROELECTRONICS

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Communication device drivers

UM0851

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Doc ID 16604 Rev 2

There are certainly other configurations related to the USB Device which may be required

for an individual application. One of these is FIFO related configurations. The RxFIFO on

SPEAr USBD can be configured for each endpoint. Keep in mind that total combined

RxFIFO usage for all out endpoints should not exceed 2 KB. Similarly, total combined

TxFIFO usage for all IN endpoints should be limited to 2 KB.

To change this FIFO configuration, you can edit the corresponding macro in

drivers/usb/gadget/spr_udc_syn.h.

/* Default Endpoint FIFO sizes in words */

#define EP1_IN_FIFO_SIZE

512/4

#define EP2_OUT_FIFO_SIZE

512/4

...

Buffer length configuration

The gadget drivers allocate a USB request and then submit it to the framework for transfer.

The length of such transfer requests will determine the performance of the driver. Allocating

a large buffer and hence a bigger buffer length will make CPU more free. USB DMA would

try to complete the transfer for the asked length and then interrupt CPU notifying the

completion of the transfer.

Note:

The maximum buffer length is limited to 65535 bytes on SPEAr USB Device.

4.4.7

References

●

http://www.linux-usb.org/gadgets

●

http://www.linux-usb.org/usbtest/

●

http://www.usb.org/

4.5

I2C driver

This section describes the driver for the I2C controller embedded in SPEAr. The IP is

provided by Synopsis.

4.5.1

Hardware overview

I2C is a multi-master serial computer bus invented by Philips that is used to attach low-

speed peripherals to a motherboard, embedded system, or cell phone. It is a master-slave

protocol, where communication takes place between a host adapter (or host controller) and

client devices (or slaves).

CONFIG_USB_GADGET_SPEAR_SYN

This enables SPEAr USB Device controller

support

CONFIG_USB_TEST

This enables USB test module for testing zero

gadget on host side.

CONFIG_USB_GADGET_DUALSPEED

This enables dual (FULL and HIGH) speed

support.

Table 25.

Linux kernel configuration (continued)

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