Import otp from rp-hal, helper fns for chipid and randid

Again, credit to @thejpster for doing the hard part and figuring out the
otp.

3 files changed, 156 insertions, 0 deletions

diff --git a/embassy-rp/src/lib.rs b/embassy-rp/src/lib.rs
index f8fcfe52b..c357c14c2 100644
--- a/embassy-rp/src/lib.rs
+++ b/embassy-rp/src/lib.rs
@@ -32,6 +32,8 @@ pub mod gpio;
 pub mod i2c;
 pub mod i2c_slave;
 pub mod multicore;
+#[cfg(feature = "_rp235x")]
+pub mod otp;
 pub mod pwm;
 mod reset;
 pub mod rom_data;
diff --git a/embassy-rp/src/otp.rs b/embassy-rp/src/otp.rs
new file mode 100644
index 000000000..cdaf5bded
--- /dev/null
+++ b/embassy-rp/src/otp.rs
@@ -0,0 +1,108 @@
+//! Interface to the RP2350's One Time Programmable Memory
+
+// Credit: taken from `rp-hal` (also licensed Apache+MIT)
+// https://github.com/rp-rs/rp-hal/blob/main/rp235x-hal/src/rom_data.rs
+
+/// The ways in which we can fail to read OTP
+#[derive(Debug, Clone)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum Error {
+    /// The user passed an invalid index to a function.
+    InvalidIndex,
+    /// The hardware refused to let us read this word, probably due to
+    /// read lock set earlier in the boot process.
+    InvalidPermissions,
+}
+
+/// OTP read address, using automatic Error Correction.
+///
+/// A 32-bit read returns the ECC-corrected data for two neighbouring rows, or
+/// all-ones on permission failure. Only the first 8 KiB is populated.
+pub const OTP_DATA_BASE: *const u32 = 0x4013_0000 as *const u32;
+
+/// OTP read address, without using any automatic Error Correction.
+///
+/// A 32-bit read returns 24-bits of raw data from the OTP word.
+pub const OTP_DATA_RAW_BASE: *const u32 = 0x4013_4000 as *const u32;
+
+/// How many pages in OTP (post error-correction)
+pub const NUM_PAGES: usize = 64;
+
+/// How many rows in one page in OTP (post error-correction)
+pub const NUM_ROWS_PER_PAGE: usize = 64;
+
+/// How many rows in OTP (post error-correction)
+pub const NUM_ROWS: usize = NUM_PAGES * NUM_ROWS_PER_PAGE;
+
+/// Read one ECC protected word from the OTP
+pub fn read_ecc_word(row: usize) -> Result<u16, Error> {
+    if row >= NUM_ROWS {
+        return Err(Error::InvalidIndex);
+    }
+    // First do a raw read to check permissions
+    let _ = read_raw_word(row)?;
+    // One 32-bit read gets us two rows
+    let offset = row >> 1;
+    // # Safety
+    //
+    // We checked this offset was in range already.
+    let value = unsafe { OTP_DATA_BASE.add(offset).read() };
+    if (row & 1) == 0 {
+        Ok(value as u16)
+    } else {
+        Ok((value >> 16) as u16)
+    }
+}
+
+/// Read one raw word from the OTP
+///
+/// You get the 24-bit raw value in the lower part of the 32-bit result.
+pub fn read_raw_word(row: usize) -> Result<u32, Error> {
+    if row >= NUM_ROWS {
+        return Err(Error::InvalidIndex);
+    }
+    // One 32-bit read gets us one row
+    // # Safety
+    //
+    // We checked this offset was in range already.
+    let value = unsafe { OTP_DATA_RAW_BASE.add(row).read() };
+    if value == 0xFFFF_FFFF {
+        Err(Error::InvalidPermissions)
+    } else {
+        Ok(value)
+    }
+}
+
+/// Get the random 64bit chipid from rows 0x0-0x3.
+pub fn get_chipid() -> Result<u64, Error> {
+    let w0 = read_ecc_word(0x000)?.to_be_bytes();
+    let w1 = read_ecc_word(0x001)?.to_be_bytes();
+    let w2 = read_ecc_word(0x002)?.to_be_bytes();
+    let w3 = read_ecc_word(0x003)?.to_be_bytes();
+
+    Ok(u64::from_be_bytes([
+        w3[0], w3[1], w2[0], w2[1], w1[0], w1[1], w0[0], w0[1],
+    ]))
+}
+
+/// Get the 128bit private random number from rows 0x4-0xb.
+///
+/// This ID is not exposed through the USB PICOBOOT GET_INFO command
+/// or the ROM get_sys_info() API. However note that the USB PICOBOOT OTP
+/// access point can read the entirety of page 0, so this value is not
+/// meaningfully private unless the USB PICOBOOT interface is disabled via the
+//// DISABLE_BOOTSEL_USB_PICOBOOT_IFC flag in BOOT_FLAGS0
+pub fn get_private_random_number() -> Result<u128, Error> {
+    let w0 = read_ecc_word(0x004)?.to_be_bytes();
+    let w1 = read_ecc_word(0x005)?.to_be_bytes();
+    let w2 = read_ecc_word(0x006)?.to_be_bytes();
+    let w3 = read_ecc_word(0x007)?.to_be_bytes();
+    let w4 = read_ecc_word(0x008)?.to_be_bytes();
+    let w5 = read_ecc_word(0x009)?.to_be_bytes();
+    let w6 = read_ecc_word(0x00a)?.to_be_bytes();
+    let w7 = read_ecc_word(0x00b)?.to_be_bytes();
+
+    Ok(u128::from_be_bytes([
+        w7[0], w7[1], w6[0], w6[1], w5[0], w5[1], w4[0], w4[1], w3[0], w3[1], w2[0], w2[1], w1[0], w1[1], w0[0], w0[1],
+    ]))
+}
diff --git a/examples/rp23/src/bin/otp.rs b/examples/rp23/src/bin/otp.rs
new file mode 100644
index 000000000..c4d79c6ea
--- /dev/null
+++ b/examples/rp23/src/bin/otp.rs
@@ -0,0 +1,46 @@
+//! This example shows reading the OTP constants on the RP235x.
+
+#![no_std]
+#![no_main]
+
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_rp::block::ImageDef;
+use embassy_rp::otp;
+use embassy_time::Timer;
+use {defmt_rtt as _, panic_probe as _};
+
+#[link_section = ".start_block"]
+#[used]
+pub static IMAGE_DEF: ImageDef = ImageDef::secure_exe();
+
+// Program metadata for `picotool info`
+#[link_section = ".bi_entries"]
+#[used]
+pub static PICOTOOL_ENTRIES: [embassy_rp::binary_info::EntryAddr; 4] = [
+    embassy_rp::binary_info::rp_program_name!(c"OTP Read Example"),
+    embassy_rp::binary_info::rp_cargo_version!(),
+    embassy_rp::binary_info::rp_program_description!(c"OTP Read Example"),
+    embassy_rp::binary_info::rp_program_build_attribute!(),
+];
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let _ = embassy_rp::init(Default::default());
+    //
+    // add some delay to give an attached debug probe time to parse the
+    // defmt RTT header. Reading that header might touch flash memory, which
+    // interferes with flash write operations.
+    // https://github.com/knurling-rs/defmt/pull/683
+    Timer::after_millis(10).await;
+
+    let unique_id = unwrap!(otp::get_unique_id());
+    info!("Unique id:{:X}", unique_id);
+
+    let private_rand = unwrap!(otp::get_private_random_number());
+    info!("Private Rand:{:X}", private_rand);
+
+    loop {
+        Timer::after_secs(1).await;
+    }
+}