Report device unique ID as USB serial number

firmware/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
-name = "ffp"
-version = "0.1.0"
+name = "ffp_firmware"
+version = "1.0.0"
 authors = ["Adam Greig <adam@adamgreig.com>"]
 edition = "2018"
 

firmware/src/hal/mod.rs

@@ -9,3 +9,4 @@ pub mod dma;
 pub mod spi;
 pub mod usb;
 pub mod bootload;
+pub mod unique_id;

firmware/src/hal/unique_id.rs

@@ -0,0 +1,37 @@
+// Copyright 2019 Adam Greig
+// Dual licensed under the Apache 2.0 and MIT licenses.
+
+static HEX_DIGITS: [u8; 16] = [
+    48, 49, 50, 51, 52, 53, 54, 55, 56, 57,
+    97, 98, 99, 100, 101, 102,
+];
+
+/// Returns the 12-byte (96-bit) unique ID
+pub fn get_id() -> [u8; 12] {
+    // UNSAFE: Reads fixed memory address known to contain unqiue ID.
+    unsafe { read_id() }
+}
+
+/// Returns the unique ID as ASCII hex
+pub fn get_hex_id() -> [u8; 24] {
+    let id = get_id();
+    let mut out = [0u8; 24];
+    for (idx, v) in id.iter().enumerate() {
+        let v1 = v & 0x0F;
+        let v2 = (v & 0xF0) >> 4;
+        out[idx*2] = HEX_DIGITS[v1 as usize];
+        out[idx*2+1] = HEX_DIGITS[v2 as usize];
+    }
+    out
+}
+
+unsafe fn read_id() -> [u8; 12] {
+    let id1: [u8; 4] = (*(0x1FFF_F7AC as *const u32)).to_le_bytes();
+    let id2: [u8; 4] = (*(0x1FFF_F7B0 as *const u32)).to_le_bytes();
+    let id3: [u8; 4] = (*(0x1FFF_F7B4 as *const u32)).to_le_bytes();
+    [
+        id1[0], id1[1], id1[2], id1[3],
+        id2[0], id2[1], id2[2], id2[3],
+        id3[0], id3[1], id3[2], id3[3],
+    ]
+}

firmware/src/hal/usb/descriptors.rs

@@ -5,7 +5,8 @@ use core::mem::size_of;
 use super::packets::*;
 
 pub static STRING_LANGS: [u16; 1] = [0x0409];
-pub static STRINGS: [&str; 3] = ["AGG", "FFP r1", "001"];
+pub static STRING_MFN: &str = "AGG";
+pub static STRING_PRD: &str = "FFP r1";
 
 // Assigned by http://pid.codes/1209/FF50/
 const VENDOR_ID: u16 = 0x1209;

firmware/src/hal/usb/mod.rs

@@ -13,6 +13,7 @@ use buffers::*;
 use descriptors::*;
 
 use crate::app::{PinState, Mode, Request};
+use crate::hal::unique_id::get_hex_id;
 
 /// USB stack interface
 pub struct USB {
@@ -362,7 +363,7 @@ impl USB {
                 let mut desc = StringDescriptor {
                     bLength: 2 + 2 * STRING_LANGS.len() as u8,
                     bDescriptorType: DescriptorType::String as u8,
-                    bString: [0u8; 32],
+                    bString: [0u8; 48],
                 };
                 // Pack the u16 language codes into the u8 array
                 for (idx, lang) in STRING_LANGS.iter().enumerate() {
@@ -373,16 +374,29 @@ impl USB {
                 desc
             },
 
-            // Handle all other strings
-            idx if idx as usize <= STRINGS.len() => {
+            // Handle manufacturer, product, and serial number strings
+            1 | 2 | 3 => {
+                let id;
+                let string = match idx {
+                    1 => Ok(STRING_MFN),
+                    2 => Ok(STRING_PRD),
+                    3 => { id = get_hex_id(); core::str::from_utf8(&id) },
+                    _ => unreachable!(),
+                };
+                let string = match string {
+                    Ok(s) => s,
+                    Err(_) => {
+                        self.control_stall();
+                        return;
+                    }
+                };
                 let mut desc = StringDescriptor {
-                    bLength: 2 + 2 * STRINGS[idx as usize - 1].len() as u8,
+                    bLength: 2 + 2 * string.len() as u8,
                     bDescriptorType: DescriptorType::String as u8,
-                    bString: [0u8; 32],
+                    bString: [0u8; 48],
                 };
                 // Encode the &str to an iter of u16 and pack them
-                let string = STRINGS[idx as usize - 1].encode_utf16();
-                for (idx, cp) in string.enumerate() {
+                for (idx, cp) in string.encode_utf16().enumerate() {
                     let [u1, u2] = cp.to_le_bytes();
                     desc.bString[idx*2  ] = u1;
                     desc.bString[idx*2+1] = u2;

firmware/src/hal/usb/packets.rs

@@ -116,7 +116,7 @@ pub struct EndpointDescriptor {
 pub struct StringDescriptor {
     pub bLength: u8,
     pub bDescriptorType: u8,
-    pub bString: [u8; 32],
+    pub bString: [u8; 48],
 }
 
 #[allow(unused)]