[cru] Add 5ms sleep after triggering the Serial read

Author: kostorr

src/Cru/CruBar.cxx

@@ -30,6 +30,8 @@
 #include "boost/format.hpp"
 #include "Utilities/Util.h"
 
+using namespace std::literals;
+
 namespace AliceO2
 {
 namespace roc
@@ -269,6 +271,7 @@ boost::optional<int32_t> CruBar::getSerialNumber()
   uint32_t serial = readRegister(Cru::Registers::SERIAL_NUMBER.index);
   if (serial == 0x0) { // Try to populate the serial register in case it's empty
     writeRegister(Cru::Registers::SERIAL_NUMBER_CTRL.index, Cru::Registers::SERIAL_NUMBER_TRG);
+    std::this_thread::sleep_for(5ms); // Wait some time for the I2C calls
     serial = readRegister(Cru::Registers::SERIAL_NUMBER.index);
   }