Very simple but enough accuracy "Frequency Counter". Using GPS 1PPS signal for 1sec gate. CPU is F746, F446 and F411.

Dependencies:   fc_GPS1PPS_f746_f4xx iSerial mbed

Please refer following.
/users/kenjiArai/notebook/frequency-counters/

Concept block are follows.
F746
/media/uploads/kenjiArai/block_diagram_fc_f746_wo_oven.pdf
F411&F446
/media/uploads/kenjiArai/block_diagram_fc_f411_wo_oven.pdf
Hardware Circuit(common F746,F446 and F411)
/media/uploads/kenjiArai/fc_f746ng_circuit.pdf
/media/uploads/kenjiArai/f746_fc_1.jpg

Revision:
0:da29cdc50643
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/GPS_rcvr/GPSrcvr.h	Wed Nov 16 13:22:00 2016 +0000
@@ -0,0 +1,75 @@
+/*
+ * mbed Application program / GPS receiver control and 1PPS output
+ *
+ * Copyright (c) 2004,'09,'10,'16 Kenji Arai / JH1PJL
+ *  http://www.page.sannet.ne.jp/kenjia/index.html
+ *  http://mbed.org/users/kenjiArai/
+ *      Created: March     28th, 2004   Kenji Arai
+ *      updated: July      25th, 2009   for PIC24USB
+ *      updated: January   16th, 2010   change to GPS-GM318
+ *      updated: April     24th, 2010   for mbed / NXP LPC1768
+ *      Revised: Nomeber   14th, 2016
+ */
+
+//  Definition -----------------------------------------------------------------
+//  GPS data selection & buffer size
+/* $GPGAA,hhmmss.sss,ddmm.mmmmmm,N,dddmm.mmmmmm,
+        E,1,xx,xx.xx,xx.xxx,M,xx.xxx,M,s.ss,xxxx*sum<CR><LF>
+    ex. $GPGGA,060306.00,4344.77894,N,14223.38857,
+        E,2,11,0.9,128.4,M,28.8,M,5.0,0129*4C<CR><LF>
+    # of data (ex.) = 81
+*/
+#define     SIZE_BUF_GGA    96
+/*
+ $GPGSA,A,3,xx,xx,,,xx,xx,,,,,xx.x,xx.x,xx.x*sum<CR><LF>
+    ex. $GPGSA,A,3,03,06,13,16,21,23,24,25,29,31,42,50,1.9,0.9,1.7*3C
+    # of data (ex.) = 63
+*/
+#define     SIZE_BUF_GSA    80
+/*
+ $GPGSV,x,x,xx*sum<CR><LF>
+    ex. $GPGSV,3,1,12,03,39,225,47,06,55,217,48,13,21,314,48,16,74,342,50*76
+        $GPGSV,3,2,12,21,33,095,50,23,32,280,50,24,18,049,42,25,12,315,43*7E
+        $GPGSV,3,3,12,29,12,047,45,31,49,146,49,42,39,183,46,50,39,176,42*7C
+    # of data (ex.) = 70
+*/
+#define     SIZE_BUF_GSV    80
+/*
+ $GPRMC,hhmmss.sss,V,ddmm.mmmm,N,dddmm.mmmm,E,k.kkk,x.xx,ddmmyy,,,N*sum<CR><LF>
+    ex. $GPRMC,060309.00,A,4344.77571,N,14223.38879,
+            E,0.03,210.32,190808,06.2,W,D*51
+    # of data (ex.) = 84
+*/
+#define     SIZE_BUF_RMC    96
+/*
+ $GPVTG,xx.xx,T,,M,x.xx,N,x.xx,K,A*sum<CR><LF>
+    ex. $GPVTG,210.32,T,204.30,M,0.03,N,0.06,K,D*3F
+    # of data (ex.) = 43
+*/
+#define     SIZE_BUF_VTG    64
+/*
+ $GPZDA,hhmmss.sss,dd,mmm,yyyy,hh,mm*sum<CR><LF>
+    ex. $GPZDA,060307.00,19,08,2008,13,26*6E
+    # of data (ex.) = 36
+*/
+#define     SIZE_BUF_ZDA    48
+/*
+ $GPGLL,ddmm.mmmmmm,N,dddmm.mmmmmm,E,hhmmss.sss,V,D*sum<CR><LF>
+    ex. $GPGLL,4344.77956,N,14223.38863,E,060305.00,A,D*61
+    # of data (ex.) = 52
+*/
+#define     SIZE_BUF_GLL    64
+
+#define     ERR             0xff
+
+//------------------------------------------------------------------------------
+
+#ifndef _IGPSRCV_H
+#define _IGPSRCV_H
+
+void gps_data_rcv(void);    // make sure !! infinit loop on RTOS
+bool check_gps_is_okay(void);
+uint8_t check_gps_3d(void);
+
+#endif    /* _IGPSRCV_H */
+