STM32F4DISCOVERY, USB USE_ACCURATE_TIME

[bernier-paul]

Posted on February 25, 2013 at 21:49

Hi,

I use a STM32F4DISCOVERY, and I would like to begin to understant how the USB HOST/OTG works... ands it's not easy, there is a lot of files and lines of code. I saw in ST examples, that in stm32f4xx.c there is

void
TIM2_IRQHandler(
void
)

{
USB_OTG_BSP_TimerIRQ();
}

and then I saw that in usb_bsc.c it corresponds to the use of ''USE_ACCURATE_TIME''. I would like to know what's are the consequences if I removeUSE_ACCURATE_TIME and thus don't use the interrupt of TIM2. What is the purpose of the mecanismUSE_ACCURATE_TIME? I tried and it seems it still works, but is it less stable or reliable ? In addition if you have some tips to learn how usb host/otg on stm32f4 works, I'll take it ! :) Thank you !

[Tesla DeLorean]

Posted on February 26, 2013 at 01:57

What version of the library are you looking at?

Most of the ones using TIM2 assume a 72 MHz clock of the STM32F1xx series, other versions used the SysTick. The primary purpose being to generate millisecond and microsecond delays, presumably for GPIO signal placement, or reset pulses, etc.

If the code you are using doesn't utilize them, no harm dumping them. Given they are just spinning in a loop the trace unit's cycle count would be equally effective.

[bernier-paul]

Posted on March 03, 2013 at 19:21

Thank you for your answer. It's the V2.0.0 of the USB OTG/HOST libraries.

For instance the ''Audio_playback_and_record'' example from the set of 22 examples dedicated to the STM32F4DISCOVERY (http://www.st.com/web/en/catalog/tools/PF257904) uses the TIM2 interrupt (seen in stm32f4xx_it.c) . I don't know if not using it is a big issue...

[Tesla DeLorean]

Posted on March 03, 2013 at 22:09

You'll observe that in both

STM32F4-Discovery_FW_V1.1.0\Project\FW_upgrade\src\usb_bsp.c

STM32F4-Discovery_FW_V1.1.0\Project\Audio_playback_and_record\src\usb_bsp.c

The ''accurate'' clock for the BSP is based on a 72 MHz clock source, this code is not consistent with the 168 MHz the F4 uses in the project.

It's used within the following for a VBus delay

STM32F4-Discovery_FW_V1.1.0\Project\Audio_playback_and_record\src\usb_bsp.c

The following use the timer for an enumeration delay

STM32F4-Discovery_FW_V1.1.0\Project\Audio_playback_and_record\src\usbh_usr.c

Look for the usage

USB_OTG_BSP_uDelay()

USB_OTG_BSP_mDelay()

BSP_Delay() << less of any issue as it's static and not exported

I'd probably port it to using SysTick or the DWT_CYCCNT