[USB] Manage internal pull-up

On STM32L1xx, an internal pull-up resistor (1.5 kΩ) can be
connected by software on the USB data + (DP) line.
This internal pull-up resistor is enabled if the USB is
not in power-down mode and if the USB_PU bit is set.

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

cores/arduino/stm32/usb/usbd_if.c

@@ -9,6 +9,7 @@
 
 #include "usbd_if.h"
 #include "usbd_cdc_if.h"
+#include "stm32yyxx_ll_system.h"
 
 #if !defined(USBD_REENUM_DISABLED)
 
@@ -73,7 +74,7 @@
 #endif /* (defined(USBD_DETACH_PIN) || defined(USBD_ATTACH_PIN)) && defined(USBD_FIXED_PULLUP) */
 
 /* Either of these bits indicate that there are internal pullups */
-#if defined(USB_BCDR_DPPU) || defined(USB_OTG_DCTL_SDIS)
+#if defined(USB_BCDR_DPPU) || defined(USB_OTG_DCTL_SDIS) || defined(SYSCFG_PMC_USB_PU)
   #define USBD_HAVE_INTERNAL_PULLUPS
 #endif /* defined(USB_BCDR_DPPU) || defined(USB_OTG_DCTL_SDIS) */
 
@@ -144,9 +145,22 @@ WEAK void USBD_reenumerate(void)
   digitalWriteFast(USBD_PULLUP_CONTROL_PINNAME, USBD_ATTACH_LEVEL);
 #endif /* defined(USBD_PULLUP_CONTROL_FLOATING) */
 #elif defined(USBD_HAVE_INTERNAL_PULLUPS)
+#if defined(SYSCFG_PMC_USB_PU)
+  /**
+   * STM32L1xx USB_DevDisconnect() and USB_DevConnect()
+   * do not manage the internal pull-up, so manage
+   * internal pull-up manually.
+   */
+  __HAL_RCC_SYSCFG_CLK_ENABLE();
+  LL_SYSCFG_DisableUSBPullUp();
+  delay(USBD_ENUM_DELAY);
+  LL_SYSCFG_EnableUSBPullUp();
+
+#else
   USB_DevDisconnect(USBD_USB_INSTANCE);
   delay(USBD_ENUM_DELAY);
   USB_DevConnect(USBD_USB_INSTANCE);
+#endif
 #else
 #warning "No USB attach/detach method, USB might not be reliable through system resets"
 #endif