Merge #220

220: Implement accessing FPSCR r=adamgreig a=bugadani

On the nRF52, sometimes it is necessary to manipulate the FPSCR register, otherwise the device wakes up immediately from sleep. (At least on this device) the FPSCR is only available through `vmrs` instructions.

I've implemented reading the register, parsing its bits and writing a raw value to the register, but let me know if I should also implement manipulation of the named bits.

I would also like to request some assistance to get this to actually build, it's not clear to me how `.s` files are compiled in this library. I'm also not certain where the actual place for this would be - in the registers, or in the `fpu` module.

Co-authored-by: Dániel Buga <bugadani@gmail.com>
Co-authored-by: Dániel Buga <daniel@revolutionrobotics.org>

2 files changed, 350 insertions, 0 deletions

diff --git a/src/register/fpscr.rs b/src/register/fpscr.rs
new file mode 100644
index 0000000..569d3a7
--- /dev/null
+++ b/src/register/fpscr.rs
@@ -0,0 +1,343 @@
+//! Floating-point Status Control Register
+
+/// Floating-point Status Control Register
+#[allow(clippy::missing_inline_in_public_items)]
+#[derive(Clone, Copy, Debug)]
+pub struct Fpscr {
+    bits: u32,
+}
+
+impl Fpscr {
+    /// Creates a `Fspcr` value from raw bits.
+    #[inline]
+    pub fn from_bits(bits: u32) -> Self {
+        Self { bits }
+    }
+
+    /// Returns the contents of the register as raw bits
+    #[inline]
+    pub fn bits(self) -> u32 {
+        self.bits
+    }
+
+    /// Read the Negative condition code flag
+    #[inline]
+    pub fn n(self) -> bool {
+        self.bits & (1 << 31) != 0
+    }
+
+    /// Sets the Negative condition code flag
+    #[inline]
+    pub fn set_n(&mut self, n: bool) {
+        let mask = 1 << 31;
+        match n {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Zero condition code flag
+    #[inline]
+    pub fn z(self) -> bool {
+        self.bits & (1 << 30) != 0
+    }
+
+    /// Sets the Zero condition code flag
+    #[inline]
+    pub fn set_z(&mut self, z: bool) {
+        let mask = 1 << 30;
+        match z {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Carry condition code flag
+    #[inline]
+    pub fn c(self) -> bool {
+        self.bits & (1 << 29) != 0
+    }
+
+    /// Sets the Carry condition code flag
+    #[inline]
+    pub fn set_c(&mut self, c: bool) {
+        let mask = 1 << 29;
+        match c {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Overflow condition code flag
+    #[inline]
+    pub fn v(self) -> bool {
+        self.bits & (1 << 28) != 0
+    }
+
+    /// Sets the Zero condition code flag
+    #[inline]
+    pub fn set_v(&mut self, v: bool) {
+        let mask = 1 << 28;
+        match v {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Alternative Half Precision bit
+    #[inline]
+    pub fn ahp(self) -> bool {
+        self.bits & (1 << 26) != 0
+    }
+
+    /// Sets the Alternative Half Precision bit
+    #[inline]
+    pub fn set_ahp(&mut self, ahp: bool) {
+        let mask = 1 << 26;
+        match ahp {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Default NaN mode bit
+    #[inline]
+    pub fn dn(self) -> bool {
+        self.bits & (1 << 25) != 0
+    }
+
+    /// Sets the Default NaN mode bit
+    #[inline]
+    pub fn set_dn(&mut self, dn: bool) {
+        let mask = 1 << 25;
+        match dn {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Flush to Zero mode bit
+    #[inline]
+    pub fn fz(self) -> bool {
+        self.bits & (1 << 24) != 0
+    }
+
+    /// Sets the Flush to Zero mode bit
+    #[inline]
+    pub fn set_fz(&mut self, fz: bool) {
+        let mask = 1 << 24;
+        match fz {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Rounding Mode control field
+    #[inline]
+    pub fn rmode(self) -> RMode {
+        match (self.bits & (3 << 22)) >> 22 {
+            0 => RMode::Nearest,
+            1 => RMode::PlusInfinity,
+            2 => RMode::MinusInfinity,
+            _ => RMode::Zero,
+        }
+    }
+
+    /// Sets the Rounding Mode control field
+    #[inline]
+    pub fn set_rmode(&mut self, rmode: RMode) {
+        let mask = 3 << 22;
+        match rmode {
+            RMode::Nearest => self.bits = self.bits & !mask,
+            RMode::PlusInfinity => self.bits = (self.bits & !mask) | (1 << 22),
+            RMode::MinusInfinity => self.bits = (self.bits & !mask) | (2 << 22),
+            RMode::Zero => self.bits = self.bits | mask,
+        }
+    }
+
+    /// Read the Input Denormal cumulative exception bit
+    #[inline]
+    pub fn idc(self) -> bool {
+        self.bits & (1 << 7) != 0
+    }
+
+    /// Sets the Input Denormal cumulative exception bit
+    #[inline]
+    pub fn set_idc(&mut self, idc: bool) {
+        let mask = 1 << 7;
+        match idc {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Inexact cumulative exception bit
+    #[inline]
+    pub fn ixc(self) -> bool {
+        self.bits & (1 << 4) != 0
+    }
+
+    /// Sets the Inexact cumulative exception bit
+    #[inline]
+    pub fn set_ixc(&mut self, ixc: bool) {
+        let mask = 1 << 4;
+        match ixc {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Underflow cumulative exception bit
+    #[inline]
+    pub fn ufc(self) -> bool {
+        self.bits & (1 << 3) != 0
+    }
+
+    /// Sets the Underflow cumulative exception bit
+    #[inline]
+    pub fn set_ufc(&mut self, ufc: bool) {
+        let mask = 1 << 3;
+        match ufc {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Overflow cumulative exception bit
+    #[inline]
+    pub fn ofc(self) -> bool {
+        self.bits & (1 << 2) != 0
+    }
+
+    /// Sets the Overflow cumulative exception bit
+    #[inline]
+    pub fn set_ofc(&mut self, ofc: bool) {
+        let mask = 1 << 2;
+        match ofc {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Division by Zero cumulative exception bit
+    #[inline]
+    pub fn dzc(self) -> bool {
+        self.bits & (1 << 1) != 0
+    }
+
+    /// Sets the Division by Zero cumulative exception bit
+    #[inline]
+    pub fn set_dzc(&mut self, dzc: bool) {
+        let mask = 1 << 1;
+        match dzc {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+
+    /// Read the Invalid Operation cumulative exception bit
+    #[inline]
+    pub fn ioc(self) -> bool {
+        self.bits & (1 << 0) != 0
+    }
+
+    /// Sets the Invalid Operation cumulative exception bit
+    #[inline]
+    pub fn set_ioc(&mut self, ioc: bool) {
+        let mask = 1 << 0;
+        match ioc {
+            true => self.bits |= mask,
+            false => self.bits &= !mask,
+        }
+    }
+}
+
+/// Rounding mode
+#[allow(clippy::missing_inline_in_public_items)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum RMode {
+    /// Round to Nearest (RN) mode. This is the reset value.
+    Nearest,
+    /// Round towards Plus Infinity (RP) mode.
+    PlusInfinity,
+    /// Round towards Minus Infinity (RM) mode.
+    MinusInfinity,
+    /// Round towards Zero (RZ) mode.
+    Zero,
+}
+
+impl RMode {
+    /// Is Nearest the current rounding mode?
+    #[inline]
+    pub fn is_nearest(self) -> bool {
+        self == RMode::Nearest
+    }
+
+    /// Is Plus Infinity the current rounding mode?
+    #[inline]
+    pub fn is_plus_infinity(self) -> bool {
+        self == RMode::PlusInfinity
+    }
+
+    /// Is Minus Infinity the current rounding mode?
+    #[inline]
+    pub fn is_minus_infinity(self) -> bool {
+        self == RMode::MinusInfinity
+    }
+
+    /// Is Zero the current rounding mode?
+    #[inline]
+    pub fn is_zero(self) -> bool {
+        self == RMode::Zero
+    }
+}
+
+/// Read the FPSCR register
+#[inline]
+pub fn read() -> Fpscr {
+    match () {
+        #[cfg(all(cortex_m, feature = "inline-asm"))]
+        () => {
+            let r: u32;
+            unsafe {
+                llvm_asm!("vmrs $0, fpscr" : "=r"(r) ::: "volatile");
+            }
+            Fpscr::from_bits(r)
+        }
+
+        #[cfg(all(cortex_m, not(feature = "inline-asm")))]
+        () => unsafe {
+            extern "C" {
+                fn __get_FPSCR() -> u32;
+            }
+            Fpscr::from_bits(__get_FPSCR())
+        },
+
+        #[cfg(not(cortex_m))]
+        () => unimplemented!(),
+    }
+}
+
+/// Set the value of the FPSCR register
+#[inline]
+pub unsafe fn write(_fspcr: Fpscr) {
+    match () {
+        #[cfg(all(cortex_m, feature = "inline-asm"))]
+        () => {
+            let bits = _fspcr.bits();
+            llvm_asm!("vmsr fpscr, $0" :: "r"(bits) :: "volatile");
+        }
+
+        #[cfg(all(cortex_m, not(feature = "inline-asm")))]
+        () => {
+            extern "C" {
+                fn __set_FPSCR(bits: u32);
+            }
+
+            __set_FPSCR(_fspcr.bits());
+        }
+
+        #[cfg(not(cortex_m))]
+        () => unimplemented!(),
+    }
+}
diff --git a/src/register/mod.rs b/src/register/mod.rs
index d69c1a5..efbe6ef 100644
--- a/src/register/mod.rs
+++ b/src/register/mod.rs
@@ -22,6 +22,10 @@
 //! - BASEPRI
 //! - FAULTMASK
 //!
+//! The following registers are only available for devices with an FPU:
+//!
+//! - FPSCR
+//!
 //! # References
 //!
 //! - Cortex-M* Devices Generic User Guide - Section 2.1.3 Core registers
@@ -37,6 +41,9 @@ pub mod control;
 #[cfg(all(not(armv6m), not(armv8m_base)))]
 pub mod faultmask;
 
+#[cfg(has_fpu)]
+pub mod fpscr;
+
 pub mod msp;
 
 pub mod primask;