Working! with print formatting and everything!

usbscale.c

@@ -1,21 +1,36 @@
 #include <stdio.h>
 #include <sys/types.h>
+#include <stdint.h>
+#include <math.h>
 
 #include <libusb-1.0/libusb.h>
 #include "scales.h"
 
-#define DEBUG 1
+//#define DEBUG
 /*
  * These constants are from libhid/include/constants.h
  * and usage based on libhid/src/hid_exchange.c
  * also vvvoutput.txt
  */
-#define HID_REPORT_GET 0x01
-#define HID_RT_INPUT 0x01
-#define WEIGH_REPORT_ID 0x06 // Scale Data Report ID
 #define WEIGH_REPORT_SIZE 0x06
 
 static libusb_device* find_scale(libusb_device**);
+static int print_scale_data(char*);
+const char* UNITS[13] = {
+    "units",        // unknown unit
+    "mg",           // milligram
+    "g",            // gram
+    "kg",           // kilogram
+    "cd",           // carat
+    "taels",        // lian
+    "gr",           // grain
+    "dwt",          // pennyweight
+    "tonnes",       // metric tons
+    "tons",         // avoir ton
+    "ozt",          // troy ounce
+    "oz",           // ounce
+    "lbs"           // pound
+};
 
 int main(void)
 {
@@ -50,15 +65,21 @@ int main(void)
 #endif
     libusb_claim_interface(handle, 0);
 
+
+
     /*
      * Try to transfer data about status
      *
-     * http://www.beyondlogic.org/usbnutshell/usb6.shtml 
+     * http://rowsandcolumns.blogspot.com/2011/02/read-from-magtek-card-swipe-reader-in.html
-     * test_libhid.c
      */
     unsigned char data[WEIGH_REPORT_SIZE];
     unsigned int len;
-    unsigned int res = libusb_interrupt_transfer(
+    unsigned int res;
+    int continue_reading = 0;
+    int scale_result = -1;
+    
+    for(;;) {
+        res= libusb_interrupt_transfer(
             handle,
             //bmRequestType => direction: in, type: class,
                     //    recipient: interface
@@ -69,11 +90,24 @@ int main(void)
             &len,
             10000 //timeout => 10 sec
             );
+
+        if(res == 0) {
+#ifdef DEBUG
             int i;
-    printf("Got %d bytes from control transfer:\n", len);
             for(i = 0; i < WEIGH_REPORT_SIZE; i++) {
                 printf("%x\n", data[i]);
             }
+#endif
+            scale_result = print_scale_data(data);
+            if(scale_result != 1)
+                break;
+        }
+        else {
+            fprintf(stderr, "Error in USB transfer\n");
+            scale_result = -1;
+            break;
+        }
+    }
     
 
     /*
@@ -86,13 +120,87 @@ int main(void)
     libusb_close(handle);
     libusb_free_device_list(devs, 1);
     libusb_exit(NULL);
+
+    return scale_result;
+}
+
+//
+// print_scale_data
+// ----------------
+//
+// **print_scale_data** takes the 6 bytes of binary data sent by the scale and
+// interprets and prints it out.
+//
+// **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(char* dat) {
+
+    static uint8_t lastStatus = 0;
+
+    uint8_t report = dat[0];
+    uint8_t status = dat[1];
+    uint8_t unit   = dat[2];
+    uint8_t expt   = dat[3];
+    long weight = dat[4] + (dat[5] << 8);
+
+    if(expt != 255 && expt != 0) {
+        weight = pow(weight, expt);
+    }
+
+    if(report != 0x03) {
+        fprintf(stderr, "Error reading scale data\n");
+        return -1;
+    }
+
+    switch(status) {
+        case 0x01:
+            fprintf(stderr, "Scale reports Fault\n");
+            return -1;
+        case 0x02:
+            if(status != lastStatus)
+                fprintf(stderr, "Scale is zero'd...\n");
+            break;
+        case 0x03:
+            if(status != lastStatus)
+                fprintf(stderr, "Weighing...\n");
+            break;
+        case 0x04:
+            printf("%ld %s\n", weight, UNITS[unit]);
             return 0;
+        case 0x05:
+            if(status != lastStatus)
+                fprintf(stderr, "Scale reports Under Zero\n");
+            break;
+        case 0x06:
+            if(status != lastStatus)
+                fprintf(stderr, "Scale reports Over Weight\n");
+            break;
+        case 0x07:
+            if(status != lastStatus)
+                fprintf(stderr, "Scale reports Calibration Needed\n");
+            break;
+        case 0x08:
+            if(status != lastStatus)
+                fprintf(stderr, "Scale reports Re-zeroing Needed!\n");
+            break;
+        default:
+            if(status != lastStatus)
+                fprintf(stderr, "Unknown status code: %d\n", status);
+            return -1;
+    }
+    
+    lastStatus = status;
+    return 1;
 }
 
 static libusb_device* find_scale(libusb_device **devs)
 {
-    if(DEBUG)
+#ifdef DEBUG
         libusb_set_debug(NULL, 3);
+#endif
 
     int i = 0;
     libusb_device* dev;
@@ -117,13 +225,15 @@ static libusb_device* find_scale(libusb_device **devs)
                  */
 #ifdef DEBUG
 
-                printf("Found scale %04x:%04x (bus %d, device %d)\n",
+                fprintf(stderr,
+                        "Found scale %04x:%04x (bus %d, device %d)\n",
                         desc.idVendor,
                         desc.idProduct,
                         libusb_get_bus_number(dev),
                         libusb_get_device_address(dev));
 
-                    printf("It has descriptors:\n\tmanufc: %d\n\tprodct: %d\n\tserial: %d\n\tclass: %d\n\tsubclass: %d\n",
+                    fprintf(stderr,
+                            "It has descriptors:\n\tmanufc: %d\n\tprodct: %d\n\tserial: %d\n\tclass: %d\n\tsubclass: %d\n",
                             desc.iManufacturer,
                             desc.iProduct,
                             desc.iSerialNumber,
@@ -139,7 +249,8 @@ static libusb_device* find_scale(libusb_device **devs)
 
                     r = libusb_get_string_descriptor_ascii(hand, desc.iManufacturer,
                             string, 256);
-                    printf("Manufacturer: %s\n", string);
+                    fprintf(stderr,
+                            "Manufacturer: %s\n", string);
                     libusb_close(hand);
 #endif
                     return dev;