Minimum Processor Clock frequency for RM46 USB Host

Jam Akh

HI,

I have implemented USBH driver for RM46 Hercules board. When I lower the frequency of processor (I am feeding it with PLL1) lower than 160 MHz, my USB host does not work, even I am not able to enumerate it. Is there any such restriction on USB Host?

I am feeding USBH controller a constant clock of 48 MHz from PLL2 and USBH interface clock is fed from PLL1->VCLK3 and I am trying to lower PLL1 frequency by maintaining VCLK3 frequency.

Thanks,

Jumshed

over 9 years ago

0 Anthony F. Seely over 9 years ago

TI__Guru 68920 points

Jumshed,

There may be a requirement to have VCLK faster than the 48MHz controller clock .. I can check. But wouldn't expect issues at 160MHz/80MHz VCLK. Where are you running when it first fails?

0 Anthony F. Seely over 9 years ago in reply to Anthony F. Seely

TI__Guru 68920 points

The USB IP core uses a 12MHz clock for registers and state machines (and a 48MHz clock for sampling the USB wire...)

There is an asynchronous bridge between the USB IP core and the bus interface that runs off VCLK. So I really doubt that there is an issue especially if your VCLK is >> 12MHz which it should be.

But did you see: e2e.ti.com/.../369302

0 Jam Akh over 9 years ago in reply to Anthony F. Seely

Intellectual 615 points

Hi Anthony,
I have already checked this e2e.ti.com/.../369302 and I considered this thing in my design and code. if processor clock is lowered than 160 Mhz USBH does not work and it is painful for me as I want to run it at lower processor frequency at least around 100-120 MHz

Thanks,
Jam

Arm-based microcontrollers

Arm-based microcontrollers forum

Minimum Processor Clock frequency for RM46 USB Host