Update nix repos

Since LLVM v15, llvm-objcopy seems to produce broken (misaligned?)
binaries, which when combined with some difficult to debug timing issues
caused by the calibrate_dac_feedback routine, would cause the
independent watchdog to kick in, and bootloop the Thermostat.

As NixOS 23.11 ships LLVM v16, upgrading to it breaks builds. Using
rust-objcopy from cargo-binutils does not help either since the pinned
version of Rust uses LLVM v15.

arm-none-eabi-objcopy doesn't have this problem, so use it instead.

See https://github.com/llvm/llvm-project/issues/58407 and
https://github.com/rust-lang/rust/issues/102983.

README.md

@@ -45,7 +45,7 @@ There are several options for flashing Thermostat. DFU requires only a micro-USB
 
 ### dfu-util on Linux
 * Install the DFU USB tool (dfu-util).
-* Convert firmware from ELF to BIN: `arm-none-eabi-objcopy -O binary thermostat thermostat.bin` (you can skip this step if using the BIN from Hydra)
+* Convert firmware from ELF to BIN: `arm-none-eabi-objcopy -O binary target/thumbv7em-none-eabihf/release/thermostat thermostat.bin` (you can skip this step if using the BIN from Hydra)
 * Connect to the Micro USB connector to Thermostat below the RJ45.
 * Add jumper to Thermostat v2.0 across 2-pin jumper adjacent to JTAG connector.
 * Cycle board power to put it in DFU update mode
@@ -264,7 +264,6 @@ with the following keys.
 | `temperature`  | Degrees Celsius | Steinhart-Hart conversion result derived from `sens` |
 | `pid_engaged`  | Boolean         | `true` if in closed-loop mode                        |
 | `i_set`        | Amperes         | TEC output current                                   |
-| `vref`         | Volts           | MAX1968 VREF (1.5 V)                                 |
 | `dac_value`    | Volts           | AD5680 output derived from `i_set`                   |
 | `dac_feedback` | Volts           | ADC measurement of the AD5680 output                 |
 | `i_tec`        | Volts           | MAX1968 TEC current monitor                          |

flake.lock

@@ -18,16 +18,16 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1691421349,
-        "narHash": "sha256-RRJyX0CUrs4uW4gMhd/X4rcDG8PTgaaCQM5rXEJOx6g=",
+        "lastModified": 1704420045,
+        "narHash": "sha256-C36QmoJd5tdQ5R9MC1jM7fBkZW9zBUqbUCsgwS6j4QU=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "011567f35433879aae5024fc6ec53f2a0568a6c4",
+        "rev": "c1be43e8e837b8dbee2b3665a007e761680f0c3d",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "nixos-23.05",
+        "ref": "nixos-23.11",
         "repo": "nixpkgs",
         "type": "github"
       }

flake.nix

@@ -1,7 +1,7 @@
 {
   description = "Firmware for the Sinara 8451 Thermostat";
 
-  inputs.nixpkgs.url = github:NixOS/nixpkgs/nixos-23.05;
+  inputs.nixpkgs.url = github:NixOS/nixpkgs/nixos-23.11;
   inputs.mozilla-overlay = { url = github:mozilla/nixpkgs-mozilla; flake = false; };
 
   outputs = { self, nixpkgs, mozilla-overlay }:
@@ -39,7 +39,7 @@
           };
         };
 
-        nativeBuildInputs = [ pkgs.llvm ];
+        nativeBuildInputs = [ pkgs.gcc-arm-embedded ];
 
         buildPhase = ''
           cargo build --release --bin thermostat
@@ -49,11 +49,12 @@
           mkdir -p $out $out/nix-support
           cp target/thumbv7em-none-eabihf/release/thermostat $out/thermostat.elf
           echo file binary-dist $out/thermostat.elf >> $out/nix-support/hydra-build-products
-          llvm-objcopy -O binary target/thumbv7em-none-eabihf/release/thermostat $out/thermostat.bin
+          arm-none-eabi-objcopy -O binary target/thumbv7em-none-eabihf/release/thermostat $out/thermostat.bin
           echo file binary-dist $out/thermostat.bin >> $out/nix-support/hydra-build-products
         '';
 
         dontFixup = true;
+        auditable = false;
       };
     in {
       packages.x86_64-linux = {
@@ -67,7 +68,8 @@
       devShell.x86_64-linux = pkgs.mkShell {
         name = "thermostat-dev-shell";
         buildInputs = with pkgs; [
-          rust openocd dfu-util
+          rust gcc-arm-embedded
+          openocd dfu-util
           ] ++ (with python3Packages; [
             numpy matplotlib
           ]);