TMS320C6748: Some question about USB function in C6748

Zhanpeng Li

Intellectual 2140 points

Part Number: TMS320C6748

Hi Team,

I have some question about USB function in TMS320C6748:

1)Can we output the clock of USB?

External devices need to be synchronized with the USB clock from customer requirement;

2)Whether this usb can be used both for Audio equipment and normal data port?

On the one hand, customer may need C6748 is used as audio input and output, On the other hand,customer also need to Pass data when they need to update their system.

brandon.

over 5 years ago

0 Rahul Prabhu over 5 years ago

TI__Guru** 116630 points

USB clock for USB2.0 and USB 1.1 clock are derived from SYSCLK2 and SYSCLK4 from PLL0. The clock can be brought out using OBSCLK/CLKOUT pin. However, please be cautious and read the foot note in section 3.7.2 of the data sheet. It clearly indicates that the CLKOUT clock output is provided as PLL observation clock, and is provided for debug purposes only. It may be routed to a test point, but should never be connected to a load. This is the only way I am aware of bringing out the device peripheral clocks.

One potential solution is drive USB clocking using reference clock on USB_REFCLKIN and then use that to clock the audio equipment MCASP also accepts external high speed clock in addition to aux clock similar to USB. Please use the spreadsheet to simulate device clocking for SYSCLK, MCASP and USB for C6748.

8715.SYS_CLK_CALC_OMAP-L138_C674X_AM18X_v1p3.xls

you may also find the MCASP clocking discussion here useful:

https://e2e.ti.com/support/processors/f/791/t/623850

Regards,

Rahul

Processors

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TMS320C6748: Some question about USB function in C6748