AP_HAL_Linux: RCInput_RPI: fix using Util class on constructor

Program received signal SIGSEGV, Segmentation fault.
0x000b8760 in Linux::UtilRPI::get_rpi_version() const ()
(gdb) bt
 #0  0x000b8760 in Linux::UtilRPI::get_rpi_version() const ()
 #1  0x000b57ac in Linux::RCInput_RPI::RCInput_RPI() ()
 #2  0x0000acfc in _GLOBAL__sub_I__ZN9HAL_LinuxC2Ev ()
 #3  0x000e1600 in __libc_csu_init ()
 #4  0x76cad228 in __libc_start_main (main=0x7efff774, argc=1994186752,
     argv=0x76cad228 <__libc_start_main+168>, init=0xe15b4 <__libc_csu_init>,
     fini=0xe1614 <__libc_csu_fini>, rtld_fini=0x76fdf464 <_dl_fini>,
     stack_end=0x7efff774) at libc-start.c:246
 #5  0x0000afa4 in _start ()

libraries/AP_HAL_Linux/RCInput_RPI.cpp

@@ -395,6 +395,8 @@ void RCInput_RPI::set_sigaction()
 
 //Initial setup of variables
 RCInput_RPI::RCInput_RPI():
+    circle_buffer{nullptr},
+    con_blocks{nullptr},
     prev_tick(0),
     delta_time(0),
     curr_tick_inc(1000/RCIN_RPI_SAMPLE_FREQ),
@@ -405,16 +407,6 @@ RCInput_RPI::RCInput_RPI():
     last_signal(228),
     state(RCIN_RPI_INITIAL_STATE)
 {
-#if CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_ERLEBRAIN2
-    int version = 2;    
-#else
-    int version = UtilRPI::from(hal.util)->get_rpi_version();
-#endif
-    set_physical_addresses(version);
-
-    //Init memory for buffer and for DMA control blocks. See comments in "init_ctrl_data()" to understand values "2" and "113"
-    circle_buffer = new Memory_table(RCIN_RPI_BUFFER_LENGTH * 2, version);
-    con_blocks = new Memory_table(RCIN_RPI_BUFFER_LENGTH * 113, version);
 }
 
 RCInput_RPI::~RCInput_RPI()
@@ -438,6 +430,14 @@ void RCInput_RPI::init_registers()
 
 void RCInput_RPI::init()
 {
+#if CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_ERLEBRAIN2
+    int version = 2;
+#else
+    int version = UtilRPI::from(hal.util)->get_rpi_version();
+#endif
+    set_physical_addresses(version);
+    circle_buffer = new Memory_table(RCIN_RPI_BUFFER_LENGTH * 2, version);
+    con_blocks = new Memory_table(RCIN_RPI_BUFFER_LENGTH * 113, version);
 
     init_registers();
     
@@ -461,6 +461,8 @@ void RCInput_RPI::init()
     curr_signal = *((uint8_t*) circle_buffer->get_page(circle_buffer->_virt_pages, curr_pointer)) & 0x10 ? 1 : 0;
     last_signal = curr_signal;
     curr_pointer++;
+
+    _initialized = true;
 }
 
 
@@ -470,6 +472,10 @@ void RCInput_RPI::_timer_tick()
     int j;
     void* x;
 
+    if (!_initialized) {
+        return;
+    }
+
     //Now we are getting address in which DMAC is writing at current moment
     dma_cb_t* ad = (dma_cb_t*) con_blocks->get_virt_addr(dma_reg[RCIN_RPI_DMA_CONBLK_AD | RCIN_RPI_DMA_CHANNEL << 8]);
     for(j = 1; j >= -1; j--){

libraries/AP_HAL_Linux/RCInput_RPI.h

@@ -112,6 +112,8 @@ private:
     uint8_t curr_signal;
     uint8_t last_signal;
 
+    bool _initialized = false;
+
     state_t state;
 
     AP_HAL::DigitalSource *enable_pin;