You can now measure the rotation speed from the interval between index pulses.

FluxEngine.cydsn/FluxEngine.cyprj

@@ -1998,6 +1998,32 @@
 </CyGuid_2f73275c-45bf-46ba-b3b1-00a2fe0c8dd8>
 <filters />
 </CyGuid_ebc4f06d-207f-49c2-a540-72acf4adabc0>
+<CyGuid_ebc4f06d-207f-49c2-a540-72acf4adabc0 type_name="CyDesigner.Common.ProjMgmt.Model.CyPrjMgmtFolderSerialize" version="3">
+<CyGuid_2f73275c-45bf-46ba-b3b1-00a2fe0c8dd8 type_name="CyDesigner.Common.ProjMgmt.Model.CyPrjMgmtBaseContainerSerialize" version="1">
+<CyGuid_31768f72-0253-412b-af77-e7dba74d1330 type_name="CyDesigner.Common.ProjMgmt.Model.CyPrjMgmtItemSerialize" version="2" name="INDEX_IRQ" persistent="">
+<Hidden v="False" />
+</CyGuid_31768f72-0253-412b-af77-e7dba74d1330>
+<CyGuid_0820c2e7-528d-4137-9a08-97257b946089 type_name="CyDesigner.Common.ProjMgmt.Model.CyPrjMgmtItemListSerialize" version="2">
+<dependencies>
+<CyGuid_8b8ab257-35d3-4473-b57b-36315200b38b type_name="CyDesigner.Common.ProjMgmt.Model.CyPrjMgmtFileSerialize" version="3" xml_contents_version="1">
+<CyGuid_31768f72-0253-412b-af77-e7dba74d1330 type_name="CyDesigner.Common.ProjMgmt.Model.CyPrjMgmtItemSerialize" version="2" name="INDEX_IRQ.c" persistent="Generated_Source\PSoC5\INDEX_IRQ.c">
+<Hidden v="False" />
+</CyGuid_31768f72-0253-412b-af77-e7dba74d1330>
+<build_action v="SOURCE_C;CortexM3;;;" />
+<PropertyDeltas />
+</CyGuid_8b8ab257-35d3-4473-b57b-36315200b38b>
+<CyGuid_8b8ab257-35d3-4473-b57b-36315200b38b type_name="CyDesigner.Common.ProjMgmt.Model.CyPrjMgmtFileSerialize" version="3" xml_contents_version="1">
+<CyGuid_31768f72-0253-412b-af77-e7dba74d1330 type_name="CyDesigner.Common.ProjMgmt.Model.CyPrjMgmtItemSerialize" version="2" name="INDEX_IRQ.h" persistent="Generated_Source\PSoC5\INDEX_IRQ.h">
+<Hidden v="False" />
+</CyGuid_31768f72-0253-412b-af77-e7dba74d1330>
+<build_action v="HEADER;;;;" />
+<PropertyDeltas />
+</CyGuid_8b8ab257-35d3-4473-b57b-36315200b38b>
+</dependencies>
+</CyGuid_0820c2e7-528d-4137-9a08-97257b946089>
+</CyGuid_2f73275c-45bf-46ba-b3b1-00a2fe0c8dd8>
+<filters />
+</CyGuid_ebc4f06d-207f-49c2-a540-72acf4adabc0>
 </dependencies>
 </CyGuid_0820c2e7-528d-4137-9a08-97257b946089>
 </CyGuid_2f73275c-45bf-46ba-b3b1-00a2fe0c8dd8>

FluxEngine.cydsn/main.c

@@ -19,6 +19,7 @@ static bool motor_on = false;
 static uint32_t motor_on_time = 0;
 static bool homed = false;
 static int current_track = 0;
+static volatile bool index_irq = false;
 
 #if 0
 static uint8_t td[BUFFER_COUNT];
@@ -36,6 +37,11 @@ static void system_timer_cb(void)
     CyGlobalIntEnable;
 }
 
+CY_ISR(index_irq_cb)
+{
+    index_irq = true;
+}
+
 static void start_motor(void)
 {
     if (!motor_on)
@@ -162,6 +168,27 @@ static void cmd_seek(struct seek_frame* f)
     send_reply(&r);    
 }
 
+static void cmd_measure_speed(struct any_frame* f)
+{
+    start_motor();
+    
+    UART_PutString("wait for index\n");
+    index_irq = false;
+    while (!index_irq)
+        ;
+    index_irq = false;
+    int start_clock = clock;
+    UART_PutString("wait for another index\n");
+    while (!index_irq)
+        ;
+    int end_clock = clock;
+    UART_PutString("done\n");
+    
+    DECLARE_REPLY_FRAME(struct speed_frame, F_FRAME_MEASURE_SPEED_REPLY);
+    r.period_ms = end_clock - start_clock;
+    send_reply((struct any_frame*) &r);    
+}
+
 static void handle_command(void)
 {
     static uint8_t input_buffer[FRAME_SIZE];
@@ -178,6 +205,10 @@ static void handle_command(void)
         case F_FRAME_SEEK_CMD:
             cmd_seek((struct seek_frame*) f);
             break;
+        
+        case F_FRAME_MEASURE_SPEED_CMD:
+            cmd_measure_speed(f);
+            break;
             
         default:
             send_error(F_ERROR_BAD_COMMAND);
@@ -189,6 +220,7 @@ int main(void)
     CyGlobalIntEnable;
     CySysTickStart();
     CySysTickSetCallback(4, system_timer_cb);
+    INDEX_IRQ_StartEx(&index_irq_cb);
     UART_Start();
     USBFS_Start(0, USBFS_DWR_VDDD_OPERATION);
     //USBFS_CDC_Init();

globals.h

@@ -20,5 +20,6 @@ extern void usb_cmd_recv(void* ptr, int len);
 
 extern int usb_get_version(void);
 extern void usb_seek(int track);
+extern int usb_measure_speed(void);
 
 #endif

main.c

@@ -47,7 +47,9 @@ int main(int argc, char* const* argv)
 
 	int v = usb_get_version();
 	printf("FluxEngine version %d\n", v);
-	usb_seek(40);
+
+	int period_ms = usb_measure_speed();
+	printf("Rotational period is %d ms (%f rpm)\n", period_ms, 60000.0/period_ms);
 
 	#if 0
 	parse_options(argc, argv);

protocol.h

@@ -25,11 +25,13 @@ enum
 
 enum
 {
-    F_FRAME_ERROR = 0,
-    F_FRAME_GET_VERSION_CMD,
-    F_FRAME_GET_VERSION_REPLY,
-    F_FRAME_SEEK_CMD,
-    F_FRAME_SEEK_REPLY,
+    F_FRAME_ERROR = 0,            /* any_frame */
+    F_FRAME_GET_VERSION_CMD,      /* any_frame */
+    F_FRAME_GET_VERSION_REPLY,    /* version_frame */
+    F_FRAME_SEEK_CMD,             /* seek_frame */
+    F_FRAME_SEEK_REPLY,           /* any_frame */
+    F_FRAME_MEASURE_SPEED_CMD,    /* any_frame */
+    F_FRAME_MEASURE_SPEED_REPLY,  /* speed_frame */
 };
 
 enum
@@ -67,4 +69,10 @@ struct seek_frame
     uint8_t track;
 };
 
+struct speed_frame
+{
+    struct frame_header f;
+    uint16_t period_ms;
+};
+
 #endif

usb.c

@@ -88,3 +88,12 @@ void usb_seek(int track)
     usb_cmd_send(&f, f.f.size);
     await_reply(F_FRAME_SEEK_REPLY);
 }
+
+int usb_measure_speed(void)
+{
+    struct any_frame f = { .f = {.type = F_FRAME_MEASURE_SPEED_CMD, .size = sizeof(f)} };
+    usb_cmd_send(&f, f.f.size);
+    struct speed_frame* r = await_reply(F_FRAME_MEASURE_SPEED_REPLY);
+    return r->period_ms;
+}
+