Added basic Bitbanging support

Author: Cor Peters

src/bb.rs

@@ -0,0 +1,48 @@
+//! Bit banding
+//!
+//! Support for the manipulation of peripheral registers through bit-banding.
+//! Not all peripherals are mapped to the bit-banding alias region, the peripheral bit-band region
+//! is from `0x4000_0000` to `0x400F_FFFF`. Bit-banding allows the manipulation of individual bits
+//! atomically.
+
+use core::ptr;
+
+// Start address of the peripheral memory region capable of being addressed by bit-banding
+const PERI_ADDRESS_START: usize = 0x4000_0000;
+const PERI_ADDRESS_END: usize = 0x400F_FFFF;
+
+const PERI_BIT_BAND_BASE: usize = 0x4200_0000;
+
+/// Clears the bit on the provided register without modifying other bits.
+///
+/// # Safety
+///
+/// Some registers have reserved bits which should not be modified.
+pub unsafe fn clear<T>(register: *const T, bit: u8) {
+    write(register, bit, false);
+}
+
+/// Sets the bit on the provided register without modifying other bits.
+///
+/// # Safety
+///
+/// Some registers have reserved bits which should not be modified.
+pub unsafe fn set<T>(register: *const T, bit: u8) {
+    write(register, bit, true);
+}
+
+/// Sets or clears the bit on the provided register without modifying other bits.
+///
+/// # Safety
+///
+/// Some registers have reserved bits which should not be modified.
+pub unsafe fn write<T>(register: *const T, bit: u8, set: bool) {
+    let addr = register as usize;
+
+    assert!(addr >= PERI_ADDRESS_START && addr <= PERI_ADDRESS_END);
+    assert!(bit < 32);
+
+    let bit = bit as usize;
+    let bb_addr = (PERI_BIT_BAND_BASE + (addr - PERI_ADDRESS_START) * 32) + 4 * bit;
+    ptr::write_volatile(bb_addr as *mut u32, if set { 1 } else { 0 });
+}

src/lib.rs

@@ -56,6 +56,7 @@ pub use stm32g4::stm32g484 as stm32;
 pub use crate::stm32::interrupt;
 
 // pub mod adc;
+pub mod bb;
 // pub mod crc;
 // pub mod dac;
 pub mod delay;