Posted on March 09, 2014 at 14:58
While the device is plugged off, it goes to Suspend.
Are you working on STSW-STM32121 (STM32_USB-FS-Device_Lib_V4.0.0)?
As the default behavior, this device stack drops the entire system into STOP mode, while USB is suspending. This feature is fine for bus-powered devices, to satisfy the suspend current requirement (less than 2.5mA) of the USB spec. But for self-powered devices, like your case, this feature is not always preferred.
You may disable suspend/resume detection by dropping CNTR_SUSPM and CNTR_ESOFM from IMR_MSK() definition in usb_conf.h
STM32_USB-FS-Device_Lib_V4.0.0/Projects/Virtual_COM_Port/inc/usb_conf.h
/* IMR_MSK */
/* mask defining which events has to be handled */
/* by the device application software */
// #define IMR_MSK (CNTR_CTRM | CNTR_WKUPM | CNTR_SUSPM | CNTR_ERRM | CNTR_SOFM \
// | CNTR_ESOFM | CNTR_RESETM )
// Disable Suspend/Resume response completely
#define IMR_MSK (CNTR_CTRM | CNTR_WKUPM | CNTR_ERRM | CNTR_SOFM | CNTR_RESETM )
OR
If you would still need suspend/resume detection, but you don't like STOP mode,
modify Suspend() code in usb_pwr.c, so that it doesn't drop in to STOP mode
STM32_USB-FS-Device_Lib_V4.0.0/Projects/Virtual_COM_Port/src/usb_pwr.c
void Suspend(void)
{
...
// delete the code after this line
/*prepare entry in low power mode (STOP mode)*/
/* Select the regulator state in STOP mode*/
...
}
Tsuneo
