3 files changed, 46 insertions, 0 deletions

diff --git a/embassy-stm32/Cargo.toml b/embassy-stm32/Cargo.toml
index 459d2e370..1f9a51678 100644
--- a/embassy-stm32/Cargo.toml
+++ b/embassy-stm32/Cargo.toml
@@ -115,6 +115,9 @@ low-power-debug-with-sleep = []
 ## Automatically generate `memory.x` file using [`stm32-metapac`](https://docs.rs/stm32-metapac/)
 memory-x = ["stm32-metapac/memory-x"]
 
+## Use secure registers when TrustZone is enabled
+trustzone-secure = []
+
 ## Re-export stm32-metapac at `embassy_stm32::pac`.
 ## This is unstable because semver-minor (non-breaking) releases of embassy-stm32 may major-bump (breaking) the stm32-metapac version.
 ## If this is an issue for you, you're encouraged to directly depend on a fixed version of the PAC.
diff --git a/embassy-stm32/src/flash/u5.rs b/embassy-stm32/src/flash/u5.rs
index 4a2168b14..ddd4d73ff 100644
--- a/embassy-stm32/src/flash/u5.rs
+++ b/embassy-stm32/src/flash/u5.rs
@@ -14,10 +14,19 @@ pub(crate) const fn get_flash_regions() -> &'static [&'static FlashRegion] {
 }
 
 pub(crate) unsafe fn lock() {
+    #[cfg(feature = "trustzone-secure")]
+    pac::FLASH.seccr().modify(|w| w.set_lock(true));
+    #[cfg(not(feature = "trustzone-secure"))]
     pac::FLASH.nscr().modify(|w| w.set_lock(true));
 }
 
 pub(crate) unsafe fn unlock() {
+    #[cfg(feature = "trustzone-secure")]
+    if pac::FLASH.seccr().read().lock() {
+        pac::FLASH.seckeyr().write_value(0x4567_0123);
+        pac::FLASH.seckeyr().write_value(0xCDEF_89AB);
+    }
+    #[cfg(not(feature = "trustzone-secure"))]
     if pac::FLASH.nscr().read().lock() {
         pac::FLASH.nskeyr().write_value(0x4567_0123);
         pac::FLASH.nskeyr().write_value(0xCDEF_89AB);
@@ -27,12 +36,20 @@ pub(crate) unsafe fn unlock() {
 pub(crate) unsafe fn enable_blocking_write() {
     assert_eq!(0, WRITE_SIZE % 4);
 
+    #[cfg(feature = "trustzone-secure")]
+    pac::FLASH.seccr().write(|w| {
+        w.set_pg(pac::flash::vals::SeccrPg::B_0X1);
+    });
+    #[cfg(not(feature = "trustzone-secure"))]
     pac::FLASH.nscr().write(|w| {
         w.set_pg(pac::flash::vals::NscrPg::B_0X1);
     });
 }
 
 pub(crate) unsafe fn disable_blocking_write() {
+    #[cfg(feature = "trustzone-secure")]
+    pac::FLASH.seccr().write(|w| w.set_pg(pac::flash::vals::SeccrPg::B_0X0));
+    #[cfg(not(feature = "trustzone-secure"))]
     pac::FLASH.nscr().write(|w| w.set_pg(pac::flash::vals::NscrPg::B_0X0));
 }
 
@@ -50,16 +67,32 @@ pub(crate) unsafe fn blocking_write(start_address: u32, buf: &[u8; WRITE_SIZE])
 }
 
 pub(crate) unsafe fn blocking_erase_sector(sector: &FlashSector) -> Result<(), Error> {
+    #[cfg(feature = "trustzone-secure")]
+    pac::FLASH.seccr().modify(|w| {
+        w.set_per(pac::flash::vals::SeccrPer::B_0X1);
+        w.set_pnb(sector.index_in_bank)
+    });
+    #[cfg(not(feature = "trustzone-secure"))]
     pac::FLASH.nscr().modify(|w| {
         w.set_per(pac::flash::vals::NscrPer::B_0X1);
         w.set_pnb(sector.index_in_bank)
     });
 
+    #[cfg(feature = "trustzone-secure")]
+    pac::FLASH.seccr().modify(|w| {
+        w.set_strt(true);
+    });
+    #[cfg(not(feature = "trustzone-secure"))]
     pac::FLASH.nscr().modify(|w| {
         w.set_strt(true);
     });
 
     let ret: Result<(), Error> = blocking_wait_ready();
+    #[cfg(feature = "trustzone-secure")]
+    pac::FLASH
+        .seccr()
+        .modify(|w| w.set_per(pac::flash::vals::SeccrPer::B_0X0));
+    #[cfg(not(feature = "trustzone-secure"))]
     pac::FLASH
         .nscr()
         .modify(|w| w.set_per(pac::flash::vals::NscrPer::B_0X0));
@@ -70,11 +103,17 @@ pub(crate) unsafe fn blocking_erase_sector(sector: &FlashSector) -> Result<(), E
 pub(crate) unsafe fn clear_all_err() {
     // read and write back the same value.
     // This clears all "write 1 to clear" bits.
+    #[cfg(feature = "trustzone-secure")]
+    pac::FLASH.secsr().modify(|_| {});
+    #[cfg(not(feature = "trustzone-secure"))]
     pac::FLASH.nssr().modify(|_| {});
 }
 
 unsafe fn blocking_wait_ready() -> Result<(), Error> {
     loop {
+        #[cfg(feature = "trustzone-secure")]
+        let sr = pac::FLASH.secsr().read();
+        #[cfg(not(feature = "trustzone-secure"))]
         let sr = pac::FLASH.nssr().read();
 
         if !sr.bsy() {
diff --git a/examples/stm32u5/Cargo.toml b/examples/stm32u5/Cargo.toml
index 03294339d..01320b88d 100644
--- a/examples/stm32u5/Cargo.toml
+++ b/examples/stm32u5/Cargo.toml
@@ -24,5 +24,9 @@ heapless = { version = "0.8", default-features = false }
 
 micromath = "2.0.0"
 
+[features]
+## Use secure registers when TrustZone is enabled
+trustzone-secure = ["embassy-stm32/trustzone-secure"]
+
 [profile.release]
 debug = 2