Delay by 25600 cycles after selecting USB PHY

Author: dgoodlad

src/bus.rs

@@ -431,6 +431,13 @@ impl<USB: UsbPeripheral> usb_device::bus::UsbBus for UsbBus<USB> {
                 }
             }
 
+            // Delay a few cycles after selecting PHY before doing a core reset
+            // https://community.st.com/s/question/0D53W00000znL7jSAE/stm32h745-usbotg-intermittently-fails-to-respond-to-core-reset
+            #[cfg(not(feature = "cortex-m"))]
+            for _ in 0..500000 {};
+            #[cfg(feature = "cortex-m")]
+            cortex_m::asm::delay(25600);
+
             // Perform core soft-reset
             while read_reg!(otg_global, regs.global(), GRSTCTL, AHBIDL) == 0 {}
             modify_reg!(otg_global, regs.global(), GRSTCTL, CSRST: 1);