Add human-readable ounce display

.github/workflows/build.yml

@@ -0,0 +1,17 @@
+name: Build
+
+on:
+  push:
+    branches: [ "master" ]
+  pull_request:
+    branches: [ "master" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install dependencies
+        run: sudo apt-get update && sudo apt-get install -y build-essential libusb-1.0-0-dev
+      - name: Build
+        run: make

50-usb-scale.rules

@@ -10,4 +10,4 @@ SUBSYSTEM=="usb", ATTR{idVendor}=="0b67", ATTR{idProduct}=="555e", MODE="0776"
 SUBSYSTEM=="usb", ATTR{idVendor}=="0922", ATTR{idProduct}=="8003", MODE="0776"
 SUBSYSTEM=="usb", ATTR{idVendor}=="0922", ATTR{idProduct}=="8004", MODE="0776"
 SUBSYSTEM=="usb", ATTR{idVendor}=="0922", ATTR{idProduct}=="8009", MODE="0776"
-SUBSYSTEM=="usb", ATTR{idVendor}=="08df", ATTR{idProduct}=="0200", MODE="0776"
+SUBSYSTEM=="usb", ATTR{idVendor}=="0d8f", ATTR{idProduct}=="0200", MODE="0776"

README.md

@@ -24,6 +24,9 @@ error messages will be sent to `stderr`. An exit code of 0 means that a scale
 was found and a weight was successfully read. Any other error code indicates
 that a weight reading was unavailable.
 
+Use the `-h`/`--human` flag to format ounce measurements as pounds and
+ounces, e.g. `1 lbs 4 oz` instead of `20 oz`.
+
 ## Zeroing the scale
 
 There is somewhat-experimental support for sending a tare command to the scale.

usbscale.c

@@ -73,7 +73,7 @@ static libusb_device* find_nth_scale(libusb_device**, int);
 // it, printing out the result to the screen. It also returns a 1 if the
 // program should read again (i.e. continue looping).
 //
-static int print_scale_data(unsigned char*);
+static int print_scale_data(unsigned char*, bool);
 
 //
 // take device and fetch bEndpointAddress for the first endpoint
@@ -107,13 +107,14 @@ const char* UNITS[13] = {
 };
 
 // Setup argument parsing
-const char *argp_program_version = "usbscale 0.2";
+const char *argp_program_version = "usbscale 0.3";
 const char *argp_program_bug_address = "<https://www.github.com/erjiang/usbscale/issues>";
 static char doc[] = "Read weight from a USB scale\n"
 "The `zero' command will request the scale to reset to zero (not supported by all scales).\n";
 static char args_doc[] = "[zero]";
 static struct argp_option options[] = {
     { "index", 'i', "INDEX", 0, "Index of scale to read (default: 1)" },
+    { "human", 'h', 0, 0, "Print weight in lbs and oz when units are oz" },
     { 0 }
 };
 
@@ -121,6 +122,7 @@ static struct argp_option options[] = {
 struct arguments {
     int index;
     bool tare;
+    bool human;
 };
 
 static error_t parse_opt(int key, char *arg, struct argp_state *state) {
@@ -133,6 +135,9 @@ static error_t parse_opt(int key, char *arg, struct argp_state *state) {
                 argp_usage(state);
             }
             break;
+        case 'h':
+            arguments->human = true;
+            break;
         case ARGP_KEY_ARG:
             if (strcmp(arg, "zero") == 0) {
                 arguments->tare = true;
@@ -162,6 +167,7 @@ int main(int argc, char **argv)
     // By default, get the first scale's weight
     arguments.index = 1;
     arguments.tare = false;
+    arguments.human = false;
     argp_parse(&argp, argc, argv, 0, 0, &arguments);
 
     libusb_device **devs;
@@ -314,7 +320,7 @@ int main(int argc, char **argv)
             }
 #endif
             if (weigh_count < 1) {
-                scale_result = print_scale_data(data);
+                scale_result = print_scale_data(data, arguments.human);
                 if(scale_result != 1)
                    break;
             }
@@ -351,14 +357,15 @@ int main(int argc, char **argv)
 // ----------------
 //
 // **print_scale_data** takes the 6 bytes of binary data sent by the scale and
-// interprets and prints it out.
+// interprets and prints it out. If `human` is true and the units are ounces,
+// it will output the weight as pounds and ounces.
 //
 // **Returns:** `0` if weight data was successfully read, `1` if the data
 // indicates that more data needs to be read (i.e. keep looping), and `-1` if
 // the scale data indicates that some error occurred and that the program
 // should terminate.
 //
-static int print_scale_data(unsigned char* dat) {
+static int print_scale_data(unsigned char* dat, bool human) {
 
     //
     // We keep around `lastStatus` so that we're not constantly printing the
@@ -376,8 +383,10 @@ static int print_scale_data(unsigned char* dat) {
     uint8_t unit   = dat[2];
     // According to the docs, scaling applied to the data as a base ten exponent
     int8_t  expt   = dat[3];
-    // convert to machine order at all times
-    double weight = (double) le16toh(dat[5] << 8 | dat[4]);
+    // combine the little-endian weight bytes without relying on system
+    // endianness. dat[4] is the low byte and dat[5] is the high byte.
+    uint16_t raw_weight = (uint16_t)dat[4] | ((uint16_t)dat[5] << 8);
+    double weight = (double)raw_weight;
     // since the expt is signed, we do not need no trickery
     weight = weight * pow(10, expt);
 
@@ -412,7 +421,13 @@ static int print_scale_data(unsigned char* dat) {
         // the `UNITS` lookup table for unit names.
         //
         case 0x04:
-            printf("%g %s\n", weight, UNITS[unit]);
+            if (human && unit == 11) {
+                int lbs = (int)floor(weight / 16.0);
+                double oz = weight - (lbs * 16.0);
+                printf("%d lbs %g oz\n", lbs, oz);
+            } else {
+                printf("%g %s\n", weight, UNITS[unit]);
+            }
             return 0;
         case 0x05:
             if(status != lastStatus)
@@ -463,8 +478,8 @@ static libusb_device* find_nth_scale(libusb_device **devs, int index)
     uint16_t last_device_address = 0;
 
     //
-    // Loop through each USB device, and for each device, loop through the
-    // scales list to see if it's one of our listed scales.
+    // Loop through each USB device and check if it's one of the
+    // supported scales listed in scales.h.
     //
     while ((dev = devs[i++]) != NULL) {
 
@@ -474,9 +489,7 @@ static libusb_device* find_nth_scale(libusb_device **devs, int index)
             fprintf(stderr, "failed to get device descriptor");
             return NULL;
         }
-        int i;
-        for (i = 0; i < NSCALES; i++) {
-            if (is_scale(desc.idVendor, desc.idProduct)) {
+        if (is_scale(desc.idVendor, desc.idProduct)) {
 
                 // Skip this device if it's the same as the last one.
                 uint16_t this_device_address = (libusb_get_bus_number(dev) << 8) + libusb_get_device_address(dev);
@@ -520,7 +533,6 @@ static libusb_device* find_nth_scale(libusb_device **devs, int index)
                 if (curr_index == index) {
                     return dev;
                 }
-            }
         }
     }
     return NULL;