diff --git a/.github/.cspell/project-dictionary.txt b/.github/.cspell/project-dictionary.txt
index e54307684..86fe0d3e7 100644
--- a/.github/.cspell/project-dictionary.txt
+++ b/.github/.cspell/project-dictionary.txt
@@ -43,6 +43,7 @@ docsrs
 doctests
 DWCAS
 endianness
+espup
 exynos
 FIQs
 getauxval
@@ -95,6 +96,7 @@ RAII
 rclass
 rcpc
 reentrancy
+rsil
 sbcs
 seqlock
 setb
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2c1e5188b..8dee9649f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -243,6 +243,9 @@ jobs:
           persist-credentials: false
       - name: Install Rust
         run: rustup toolchain add nightly --no-self-update && rustup default nightly
+      - uses: taiki-e/install-action@v2
+        with:
+          tool: espup
       - run: |
           set -euxo pipefail
           sudo apt-get -o Acquire::Retries=10 -qq update && sudo apt-get -o Acquire::Retries=10 -o Dpkg::Use-Pty=0 install -y --no-install-recommends \
@@ -259,7 +262,10 @@ jobs:
           sudo mv "opensbi-${OPENSBI_VERSION}-rv-bin/share/opensbi/ilp32/generic/firmware/fw_dynamic.bin" /usr/share/qemu/opensbi-riscv32-generic-fw_dynamic.bin
           sudo mv "opensbi-${OPENSBI_VERSION}-rv-bin/share/opensbi/ilp32/generic/firmware/fw_dynamic.elf" /usr/share/qemu/opensbi-riscv32-generic-fw_dynamic.elf
           rm -rf "opensbi-${OPENSBI_VERSION}-rv-bin"
+      - run: espup install
       - run: tools/no-std.sh
+      - run: tools/build.sh +esp xtensa-esp32-none-elf
+      # - run: tools/no-std.sh +esp xtensa-esp32-none-elf # TODO
 
   miri:
     strategy:
diff --git a/README.md b/README.md
index b270bccee..98d361778 100644
--- a/README.md
+++ b/README.md
@@ -13,7 +13,7 @@ Portable atomic types including support for 128-bit atomics, atomic float, etc.
 - Provide `AtomicI128` and `AtomicU128`.
 - Provide `AtomicF32` and `AtomicF64`. ([optional, requires the `float` feature](#optional-features-float))
 - Provide atomic load/store for targets where atomic is not available at all in the standard library. (RISC-V without A-extension, MSP430, AVR)
-- Provide atomic CAS for targets where atomic CAS is not available in the standard library. (thumbv6m, pre-v6 ARM, RISC-V without A-extension, MSP430, AVR, etc.) (always enabled for MSP430 and AVR, [optional](#optional-cfg-unsafe-assume-single-core) otherwise)
+- Provide atomic CAS for targets where atomic CAS is not available in the standard library. (thumbv6m, pre-v6 ARM, RISC-V without A-extension, MSP430, AVR, Xtensa, etc.) (always enabled for MSP430 and AVR, [optional](#optional-cfg-unsafe-assume-single-core) otherwise)
 - Provide stable equivalents of the standard library's atomic types' unstable APIs, such as [`AtomicPtr::fetch_*`](https://github.com/rust-lang/rust/issues/99108), [`AtomicBool::fetch_not`](https://github.com/rust-lang/rust/issues/98485), [`Atomic*::as_ptr`](https://github.com/rust-lang/rust/issues/66893).
 - Make features that require newer compilers, such as [fetch_max](https://doc.rust-lang.org/std/sync/atomic/struct.AtomicUsize.html#method.fetch_max), [fetch_min](https://doc.rust-lang.org/std/sync/atomic/struct.AtomicUsize.html#method.fetch_min), [fetch_update](https://doc.rust-lang.org/std/sync/atomic/struct.AtomicPtr.html#method.fetch_update), and [stronger CAS failure ordering](https://github.com/rust-lang/rust/pull/98383) available on Rust 1.34+.
 - Provide workaround for bugs in the standard library's atomic-related APIs, such as [rust-lang/rust#100650], `fence`/`compiler_fence` on MSP430 that cause LLVM error, etc.
@@ -113,7 +113,7 @@ See also the [`atomic128` module's readme](https://github.com/taiki-e/portable-a
 
   This is intentionally not an optional feature. (If this is an optional feature, dependencies can implicitly enable the feature, resulting in the use of unsound code without the end-user being aware of it.)
 
-  ARMv6-M (thumbv6m), pre-v6 ARM (e.g., thumbv4t, thumbv5te), RISC-V without A-extension are currently supported.
+  ARMv6-M (thumbv6m), pre-v6 ARM (e.g., thumbv4t, thumbv5te), RISC-V without A-extension, and Xtensa are currently supported.
 
   Since all MSP430 and AVR are single-core, we always provide atomic CAS for them without this cfg.
 
diff --git a/src/imp/interrupt/mod.rs b/src/imp/interrupt/mod.rs
index d5c38257e..340b83c8d 100644
--- a/src/imp/interrupt/mod.rs
+++ b/src/imp/interrupt/mod.rs
@@ -60,6 +60,7 @@ use arch::atomic;
 #[cfg_attr(target_arch = "avr", path = "avr.rs")]
 #[cfg_attr(target_arch = "msp430", path = "msp430.rs")]
 #[cfg_attr(any(target_arch = "riscv32", target_arch = "riscv64"), path = "riscv.rs")]
+#[cfg_attr(target_arch = "xtensa", path = "xtensa.rs")]
 mod arch;
 
 use core::{cell::UnsafeCell, sync::atomic::Ordering};
diff --git a/src/imp/interrupt/xtensa.rs b/src/imp/interrupt/xtensa.rs
new file mode 100644
index 000000000..7cbf2e6a9
--- /dev/null
+++ b/src/imp/interrupt/xtensa.rs
@@ -0,0 +1,39 @@
+// Refs:
+// - Xtensa Instruction Set Architecture (ISA) Reference Manual https://0x04.net/~mwk/doc/xtensa.pdf
+// - Linux kernel's Xtensa atomic implementation https://github.com/torvalds/linux/blob/v6.1/arch/xtensa/include/asm/atomic.h
+
+#[cfg(not(portable_atomic_no_asm))]
+use core::arch::asm;
+
+pub(super) use core::sync::atomic;
+
+pub(super) type State = u32;
+
+/// Disables interrupts and returns the previous interrupt state.
+#[inline]
+pub(super) fn disable() -> State {
+    let r: u32;
+    // SAFETY: reading mstatus and disabling interrupts is safe.
+    // (see module-level comments of interrupt/mod.rs on the safety of using privileged instructions)
+    unsafe {
+        // Do not use `nomem` and `readonly` because prevent subsequent memory accesses from being reordered before interrupts are disabled.
+        asm!("rsil {0}, 15", out(reg) r, options(nostack));
+    }
+    r
+}
+
+/// Restores the previous interrupt state.
+#[inline]
+pub(super) unsafe fn restore(r: State) {
+    // SAFETY: the caller must guarantee that the state was retrieved by the previous `disable`,
+    // and we've checked that interrupts were enabled before disabling interrupts.
+    unsafe {
+        // Do not use `nomem` and `readonly` because prevent preceding memory accesses from being reordered after interrupts are enabled.
+        asm!(
+            "wsr.ps {0}",
+            "rsync",
+            in(reg) r,
+            options(nostack),
+        );
+    }
+}
diff --git a/src/imp/mod.rs b/src/imp/mod.rs
index 8da5ef1ad..f3fdcce4f 100644
--- a/src/imp/mod.rs
+++ b/src/imp/mod.rs
@@ -152,6 +152,7 @@ mod fallback;
     target_arch = "msp430",
     target_arch = "riscv32",
     target_arch = "riscv64",
+    target_arch = "xtensa",
 ))]
 mod interrupt;
 
diff --git a/src/lib.rs b/src/lib.rs
index cbc840284..908180bed 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,7 +5,7 @@ Portable atomic types including support for 128-bit atomics, atomic float, etc.
 - Provide `AtomicI128` and `AtomicU128`.
 - Provide `AtomicF32` and `AtomicF64`. ([optional, requires the `float` feature](#optional-features-float))
 - Provide atomic load/store for targets where atomic is not available at all in the standard library. (RISC-V without A-extension, MSP430, AVR)
-- Provide atomic CAS for targets where atomic CAS is not available in the standard library. (thumbv6m, pre-v6 ARM, RISC-V without A-extension, MSP430, AVR, etc.) (always enabled for MSP430 and AVR, [optional](#optional-cfg-unsafe-assume-single-core) otherwise)
+- Provide atomic CAS for targets where atomic CAS is not available in the standard library. (thumbv6m, pre-v6 ARM, RISC-V without A-extension, MSP430, AVR, Xtensa, etc.) (always enabled for MSP430 and AVR, [optional](#optional-cfg-unsafe-assume-single-core) otherwise)
 - Provide stable equivalents of the standard library's atomic types' unstable APIs, such as [`AtomicPtr::fetch_*`](https://github.com/rust-lang/rust/issues/99108), [`AtomicBool::fetch_not`](https://github.com/rust-lang/rust/issues/98485), [`Atomic*::as_ptr`](https://github.com/rust-lang/rust/issues/66893).
 - Make features that require newer compilers, such as [fetch_max](https://doc.rust-lang.org/std/sync/atomic/struct.AtomicUsize.html#method.fetch_max), [fetch_min](https://doc.rust-lang.org/std/sync/atomic/struct.AtomicUsize.html#method.fetch_min), [fetch_update](https://doc.rust-lang.org/std/sync/atomic/struct.AtomicPtr.html#method.fetch_update), and [stronger CAS failure ordering](https://github.com/rust-lang/rust/pull/98383) available on Rust 1.34+.
 - Provide workaround for bugs in the standard library's atomic-related APIs, such as [rust-lang/rust#100650], `fence`/`compiler_fence` on MSP430 that cause LLVM error, etc.
@@ -105,7 +105,7 @@ See also the [`atomic128` module's readme](https://github.com/taiki-e/portable-a
 
   This is intentionally not an optional feature. (If this is an optional feature, dependencies can implicitly enable the feature, resulting in the use of unsound code without the end-user being aware of it.)
 
-  ARMv6-M (thumbv6m), pre-v6 ARM (e.g., thumbv4t, thumbv5te), RISC-V without A-extension are currently supported.
+  ARMv6-M (thumbv6m), pre-v6 ARM (e.g., thumbv4t, thumbv5te), RISC-V without A-extension, and Xtensa are currently supported.
 
   Since all MSP430 and AVR are single-core, we always provide atomic CAS for them without this cfg.
 
@@ -190,7 +190,7 @@ See also the [`atomic128` module's readme](https://github.com/taiki-e/portable-a
     clippy::unreadable_literal,
 )]
 // asm_experimental_arch
-// AVR and MSP430 are tier 3 platforms and require nightly anyway.
+// AVR, MSP430, and xtensa are tier 3 platforms and require nightly anyway.
 // On tier 2 platforms (powerpc64 and s390x), we use cfg set by build script to
 // determine whether this feature is available or not.
 #![cfg_attr(
@@ -199,6 +199,7 @@ See also the [`atomic128` module's readme](https://github.com/taiki-e/portable-a
         any(
             target_arch = "avr",
             target_arch = "msp430",
+            all(target_arch = "xtensa", portable_atomic_unsafe_assume_single_core),
             all(
                 portable_atomic_unstable_asm_experimental_arch,
                 target_arch = "powerpc64",
@@ -314,6 +315,7 @@ compile_error!(
             target_arch = "msp430",
             target_arch = "riscv32",
             target_arch = "riscv64",
+            target_arch = "xtensa",
         )),
     ))
 )]
@@ -327,6 +329,7 @@ compile_error!(
             target_arch = "msp430",
             target_arch = "riscv32",
             target_arch = "riscv64",
+            target_arch = "xtensa",
         )),
     ))
 )]
diff --git a/tools/build.sh b/tools/build.sh
index 8d78dd0f3..d7770ba88 100755
--- a/tools/build.sh
+++ b/tools/build.sh
@@ -121,7 +121,11 @@ is_no_std() {
 }
 
 pre_args=()
+is_custom_toolchain=''
 if [[ "${1:-}" == "+"* ]]; then
+    if [[ "$1" == "+esp" ]]; then
+        is_custom_toolchain=1
+    fi
     pre_args+=("$1")
     shift
 fi
@@ -131,7 +135,10 @@ else
     targets=("${default_targets[@]}")
 fi
 
-rustup_target_list=$(rustup ${pre_args[@]+"${pre_args[@]}"} target list)
+rustup_target_list=''
+if [[ -z "${is_custom_toolchain}" ]]; then
+    rustup_target_list=$(rustup ${pre_args[@]+"${pre_args[@]}"} target list)
+fi
 rustc_target_list=$(rustc ${pre_args[@]+"${pre_args[@]}"} --print target-list)
 rustc_version=$(rustc ${pre_args[@]+"${pre_args[@]}"} -Vv | grep 'release: ' | sed 's/release: //')
 host=$(rustc ${pre_args[@]+"${pre_args[@]}"} -Vv | grep 'host: ' | sed 's/host: //')
@@ -146,7 +153,9 @@ esac
 nightly=''
 if [[ "${rustc_version}" == *"nightly"* ]] || [[ "${rustc_version}" == *"dev"* ]]; then
     nightly=1
-    rustup ${pre_args[@]+"${pre_args[@]}"} component add rust-src &>/dev/null
+    if [[ -z "${is_custom_toolchain}" ]]; then
+        rustup ${pre_args[@]+"${pre_args[@]}"} component add rust-src &>/dev/null
+    fi
     # -Z check-cfg requires 1.63.0-nightly
     # shellcheck disable=SC2207
     if [[ "${rustc_minor_version}" -gt 62 ]] && [[ -n "${TESTS:-}" ]]; then
diff --git a/tools/no-std.sh b/tools/no-std.sh
index 22403954a..d013ef450 100755
--- a/tools/no-std.sh
+++ b/tools/no-std.sh
@@ -61,7 +61,13 @@ bail() {
 }
 
 pre_args=()
+is_custom_toolchain=''
 if [[ "${1:-}" == "+"* ]]; then
+    if [[ "$1" == "+esp" ]]; then
+        # shellcheck disable=SC1091
+        . "${HOME}/export-esp.sh"
+        is_custom_toolchain=1
+    fi
     pre_args+=("$1")
     shift
 fi
@@ -71,13 +77,18 @@ else
     targets=("${default_targets[@]}")
 fi
 
-rustup_target_list=$(rustup ${pre_args[@]+"${pre_args[@]}"} target list)
+rustup_target_list=''
+if [[ -z "${is_custom_toolchain}" ]]; then
+    rustup_target_list=$(rustup ${pre_args[@]+"${pre_args[@]}"} target list)
+fi
 rustc_target_list=$(rustc ${pre_args[@]+"${pre_args[@]}"} --print target-list)
 rustc_version=$(rustc ${pre_args[@]+"${pre_args[@]}"} -Vv | grep 'release: ' | sed 's/release: //')
 nightly=''
 if [[ "${rustc_version}" == *"nightly"* ]] || [[ "${rustc_version}" == *"dev"* ]]; then
     nightly=1
-    rustup ${pre_args[@]+"${pre_args[@]}"} component add rust-src &>/dev/null
+    if [[ -z "${is_custom_toolchain}" ]]; then
+        rustup ${pre_args[@]+"${pre_args[@]}"} component add rust-src &>/dev/null
+    fi
 fi
 
 run() {