[gnea/grbl-Mega Issue#165] Timeout while uploading for Ramps 1.4

Hello,
I’m trying to compile GRBL-MEGA for my CNC based on a RAMPS 1.4 board (arduino Mega 2560);
When I try to compile the normal version (not for ramps), it compile and upload correctly, but when I modify the lines for ramps :

“// Define CPU pin map and default settings.
// NOTE: OEMs can avoid the need to maintain/update the defaults.h and cpu_map.h files and use only
// one configuration file by placing their specific defaults and pin map at the bottom of this file.
// If doing so, simply comment out these two defines and see instructions below.
// #define DEFAULTS_GENERIC
// #define CPUMAP2560_INITIAL

// To use with RAMPS 1.4 Board, comment out the above defines and uncomment the next two defines
#define DEFAULTSRAMPSBOARD
#define CPUMAP2560RAMPSBOARD
“

it compile, but it stop uploading at 50% with the message “avrdude: stk500v2_ReceiveMessage(): timeout”

I tried using arduino 2 and arduino_CLI with the same results, so the problem is with the code, but I don’t know where to look…
Can you help me ?
Thanks,
D.