Move usb-remap internals for certain ICs to USB enable() (#119)

Move usb-remap internals for certain ICs to USB enable()

Author: brainstorm

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+- Simplify USB PA11/12 remapping for STM32F042x via `usb_bus.usb_remap()` function.
+
 ## [v0.17.0] - 2020-06-27
 
 ### Changed

examples/usb_serial.rs

@@ -15,13 +15,6 @@ use usbd_serial::{SerialPort, USB_CLASS_CDC};
 fn main() -> ! {
     let mut dp = pac::Peripherals::take().unwrap();
 
-    /* Uncomment the following lines if you have a chip in TSSOP20 (STM32F042F)
-       or UFQFPN28 (STM32F042G) package
-       This code enables clock for SYSCFG and remaps USB pins to PA9 and PA10.
-    */
-    //dp.RCC.apb2enr.modify(|_, w| w.syscfgen().set_bit());
-    //dp.SYSCFG.cfgr1.modify(|_, w| w.pa11_pa12_rmp().remapped());
-
     let mut rcc = dp
         .RCC
         .configure()
@@ -43,10 +36,20 @@ fn main() -> ! {
         pin_dm: gpioa.pa11,
         pin_dp: gpioa.pa12,
     };
+
     let usb_bus = UsbBus::new(usb);
 
     let mut serial = SerialPort::new(&usb_bus);
 
+    /*
+     * IMPORTANT: if you have a chip in TSSOP20 (STM32F042F) or UFQFPN28 (STM32F042G) package,
+     * and want to use USB, make sure you call `remap_pins(rcc, syscfg)`, otherwise the device will not enumerate.
+     *
+     * Uncomment the following function if the situation above applies to you.
+     */
+
+    //usb_bus.remap_pins();
+
     let mut usb_dev = UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0x16c0, 0x27dd))
         .manufacturer("Fake company")
         .product("Serial port")

src/usb.rs

@@ -5,7 +5,7 @@
 //! See <https://github.com/stm32-rs/stm32f0xx-hal/tree/master/examples>
 //! for usage examples.
 
-use crate::pac::{RCC, USB};
+use crate::pac::{RCC, SYSCFG, USB};
 use stm32_usbd::UsbPeripheral;
 
 use crate::gpio::gpioa::{PA11, PA12};
@@ -27,7 +27,7 @@ unsafe impl UsbPeripheral for Peripheral {
     const EP_MEMORY_SIZE: usize = 1024;
 
     fn enable() {
-        let rcc = unsafe { (&*RCC::ptr()) };
+        let rcc = unsafe { &*RCC::ptr() };
 
         cortex_m::interrupt::free(|_| {
             // Enable USB peripheral
@@ -46,4 +46,13 @@ unsafe impl UsbPeripheral for Peripheral {
     }
 }
 
+pub fn remap_pins(rcc: &mut RCC, syscfg: &mut SYSCFG) {
+    cortex_m::interrupt::free(|_| {
+        // Remap PA11/PA12 pins to PA09/PA10 for USB on
+        // TSSOP20 (STM32F042F) or UFQFPN28 (STM32F042G) packages
+        rcc.apb2enr.modify(|_, w| w.syscfgen().set_bit());
+        syscfg.cfgr1.modify(|_, w| w.pa11_pa12_rmp().remapped());
+    });
+}
+
 pub type UsbBusType = UsbBus<Peripheral>;