Use CRC32B to verify serial number

The previously used check for 0x00 or 0xFF was too primitive and
resulted in lots of false positives if other firmware was flashed.

Signed-off-by: Daniel Schaefer <dhs@frame.work>

Author: JohnAZoidberg

Cargo.lock

@@ -114,7 +114,7 @@ fn main() -> ! {
     let mut serial = SerialPort::new(&usb_bus);
 
     let serialnum = if let Some(serialnum) = get_serialnum() {
-        serialnum
+        serialnum.serialnum
     } else {
         DEFAULT_SERIAL
     };

b1display/src/main.rs

@@ -103,7 +103,7 @@ fn main() -> ! {
     let mut serial = SerialPort::new(&usb_bus);
 
     let serialnum = if let Some(serialnum) = get_serialnum() {
-        serialnum
+        serialnum.serialnum
     } else {
         DEFAULT_SERIAL
     };

c1minimal/src/main.rs

@@ -4,6 +4,7 @@ name = "fl16-inputmodules"
 version = "0.1.5"
 
 [dependencies]
+crc = "3.0"
 cortex-m = "0.7"
 cortex-m-rt = "0.7.3"
 embedded-hal = { version = "0.2.7", features = ["unproven"] }
@@ -15,7 +16,7 @@ defmt-rtt = "0.4"
 rp2040-panic-usb-boot = "0.5.0"
 
 # Not using an external BSP, we've got the Framework Laptop 16 BSPs locally in this crate
-rp2040-hal = { version="0.8", features=["rt", "critical-section-impl"] }
+rp2040-hal = { version = "0.8", features = ["rt", "critical-section-impl"] }
 rp2040-boot2 = "0.3"
 
 # USB Serial
@@ -43,6 +44,6 @@ ws2812-pio = { version = "0.6.0", optional = true }
 
 [features]
 default = []
-ledmatrix = [ "is31fl3741" ]
-b1display = [ "st7306", "embedded-graphics", "tinybmp" ]
-c1minimal = ["smart-leds", "ws2812-pio" ]
+ledmatrix = ["is31fl3741"]
+b1display = ["st7306", "embedded-graphics", "tinybmp"]
+c1minimal = ["smart-leds", "ws2812-pio"]

fl16-inputmodules/Cargo.toml

@@ -3,16 +3,43 @@ const FLASH_OFFSET: usize = 0x10000000;
 const LAST_4K_BLOCK: usize = 0xff000;
 const SERIALNUM_LEN: usize = 18;
 
-pub fn get_serialnum() -> Option<&'static str> {
+#[repr(packed)]
+pub struct SerialnumStructRaw {
+    sn_rev: u8,
+    serialnum: [u8; SERIALNUM_LEN],
+    crc32: [u8; 4],
+}
+
+pub struct SerialnumStruct {
+    pub serialnum: &'static str,
+}
+
+pub fn get_serialnum() -> Option<SerialnumStruct> {
     // Flash is mapped into memory, just read it from there
     let ptr: *const u8 = (FLASH_OFFSET + LAST_4K_BLOCK) as *const u8;
-    unsafe {
-        let slice: &[u8] = core::slice::from_raw_parts(ptr, SERIALNUM_LEN);
-        if slice[0] == 0xFF || slice[0] == 0x00 {
-            return None;
-        }
-        core::str::from_utf8(slice).ok()
+    let sn_raw_ptr = ptr as *const SerialnumStructRaw;
+    let sn_raw = unsafe { sn_raw_ptr.as_ref()? };
+
+    // Only rev 1 supported
+    if sn_raw.sn_rev != 1 {
+        return None;
     }
+
+    let crc: crc::Crc<u32> = crc::Crc::<u32>::new(&crc::CRC_32_ISO_HDLC);
+    let mut digest = crc.digest();
+    digest.update(&[sn_raw.sn_rev]);
+    digest.update(&sn_raw.serialnum);
+    let calc_checksum = digest.finalize();
+
+    let actual_checksum = u32::from_le_bytes(sn_raw.crc32);
+    // Checksum invalid, serial fall back to default serial number
+    if calc_checksum != actual_checksum {
+        return None;
+    }
+
+    Some(SerialnumStruct {
+        serialnum: core::str::from_utf8(&sn_raw.serialnum).ok()?,
+    })
 }
 
 /// Get the firmware version in a format for USB Device Release

fl16-inputmodules/src/serialnum.rs

@@ -0,0 +1,38 @@
+# Flash Layout
+
+The flash is 1MB large and consists of 256 4K blocks.
+The last block is used to store the serial number.
+
+###### LED Matrix
+
+| Start    | End      | Size          | Name               |
+|----------|----------|---------------|--------------------|
+| 0x000000 | Dynamic  | Roughly 40K   | Firmware           |
+| TBD      | 0x0FF000 | TBD           | Persistent Storage |
+| 0x0FF000 | 0x100000 | 0x1000 (4K)   | Serial Number      |
+
+###### QMK Keyboards
+
+| Start    | End      | Size          | Name               |
+|----------|----------|---------------|--------------------|
+| 0x000000 | Dynamic  | Roughly 60K   | Firmware           |
+| 0xef000  | 0x0FF000 | 0x10000 (16K) | Persistent Storage |
+| 0x0FF000 | 0x100000 | 0x01000 (4K)  | Serial Number      |
+
+## Serial Number
+
+- 1 byte serial number revision (== 1)
+- 18 bytes serial number
+- 1 byte hardware revision
+- 4 byte CRC checksum over serial number (CRC32B, same as Python's `zlib.crc32()`)
+
+Hardware Revisions:
+
+- B1 Display
+  - 1 First Prototype, very early prototype
+- LED Matrix
+  - 1 First Prototype (ATC)
+  - 2 Second Prototype (BizLink)
+  - 3 Third Prototype, 27k Resistor
+- Keyboard, Numpad, Macropad
+  - 1 First Prototype

flash_layout.md

@@ -184,7 +184,7 @@ fn main() -> ! {
     let mut serial = SerialPort::new(&usb_bus);
 
     let serialnum = if let Some(serialnum) = get_serialnum() {
-        serialnum
+        serialnum.serialnum
     } else {
         DEFAULT_SERIAL
     };

ledmatrix/src/main.rs

@@ -1,9 +1,15 @@
 #!/usr/bin/env python3
 import zlib
 
-ledmatrix_1 = b'FRAKDEAM1100000000' # POC 1
-ledmatrix_2 = b'FRAKDEBZ4100000000' # EVT 1, config 1
-ledmatrix_3 = b'FRAKDEBZ4200000000' # EVT 1, config 2 (27k resistor)
+ledmatrix_1    = b'FRAKDEAM1100000000' # POC 1
+ledmatrix_2    = b'FRAKDEBZ4100000000' # EVT 1, config 1
+ledmatrix_3    = b'FRAKDEBZ4200000000' # EVT 1, config 2 (27k resistor)
+ansi_keyboard  = b'FRAKDWEN4100000000' # EVT 1, config 1 (US ANSI)
+rgb_keyboard   = b'FRAKDKEN4100000000' # EVT 1, config 1 (US ANSI)
+iso_keyboard   = b'FRAKDWEN4200000000' # EVT 1, config 2 (UK ISO)
+jis_keyboard   = b'FRAKDWEN4J00000000' # EVT 1, config J (JIS)
+numpad         = b'FRAKDMEN4100000000' # EVT 1, config 1
+macropad       = b'FRAKDNEN4100000000' # EVT 1, config 1
 
 # This section is for modifying
 selected   = ledmatrix_2