diff --git a/armsrc/appmain.c b/armsrc/appmain.c
index 3c471191f..5908ed855 100644
--- a/armsrc/appmain.c
+++ b/armsrc/appmain.c
@@ -1154,27 +1154,27 @@ static void PacketReceived(PacketCommandNG *packet) {
 
 #ifdef WITH_EM4x50
         case CMD_LF_EM4X50_INFO: {
-            em4x50_info((em4x50_data_t *)packet->data.asBytes, true);
+            em4x50_info((const em4x50_data_t *)packet->data.asBytes, true);
             break;
         }
         case CMD_LF_EM4X50_WRITE: {
-            em4x50_write((em4x50_data_t *)packet->data.asBytes, true);
+            em4x50_write((const em4x50_data_t *)packet->data.asBytes, true);
             break;
         }
         case CMD_LF_EM4X50_WRITEPWD: {
-            em4x50_writepwd((em4x50_data_t *)packet->data.asBytes, true);
+            em4x50_writepwd((const em4x50_data_t *)packet->data.asBytes, true);
             break;
         }
         case CMD_LF_EM4X50_READ: {
-            em4x50_read((em4x50_data_t *)packet->data.asBytes, true);
+            em4x50_read((const em4x50_data_t *)packet->data.asBytes, true);
             break;
         }
         case CMD_LF_EM4X50_BRUTE: {
-            em4x50_brute((em4x50_data_t *)packet->data.asBytes, true);
+            em4x50_brute((const em4x50_data_t *)packet->data.asBytes, true);
             break;
         }
         case CMD_LF_EM4X50_LOGIN: {
-            em4x50_login((uint32_t *)packet->data.asBytes, true);
+            em4x50_login((const uint32_t *)packet->data.asBytes, true);
             break;
         }
         case CMD_LF_EM4X50_SIM: {
@@ -1184,7 +1184,7 @@ static void PacketReceived(PacketCommandNG *packet) {
             // destroy the Emulator Memory.
             //-----------------------------------------------------------------------------
             FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
-            em4x50_sim((uint32_t *)packet->data.asBytes, true);
+            em4x50_sim((const uint32_t *)packet->data.asBytes, true);
             break;
         }
         case CMD_LF_EM4X50_READER: {
@@ -1208,7 +1208,7 @@ static void PacketReceived(PacketCommandNG *packet) {
             // destroy the Emulator Memory.
             //-----------------------------------------------------------------------------
             FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
-            em4x50_chk((uint8_t *)packet->data.asBytes, true);
+            em4x50_chk((const char *)packet->data.asBytes, true);
             break;
         }
 #endif
diff --git a/armsrc/em4x50.c b/armsrc/em4x50.c
index d43a6a15f..4910caa31 100644
--- a/armsrc/em4x50.c
+++ b/armsrc/em4x50.c
@@ -634,7 +634,7 @@ static int login(uint32_t password) {
 }
 
 // searching for password using chosen bruteforce algorithm
-static bool brute(em4x50_data_t *etd, uint32_t *pwd) {
+static bool brute(const em4x50_data_t *etd, uint32_t *pwd) {
 
     generator_context_t ctx;
     bool pwd_found = false;
@@ -694,7 +694,7 @@ static bool brute(em4x50_data_t *etd, uint32_t *pwd) {
 }
 
 // login into EM4x50
-void em4x50_login(uint32_t *password, bool ledcontrol) {
+void em4x50_login(const uint32_t *password, bool ledcontrol) {
     em4x50_setup_read();
 
     int status = PM3_EFAILED;
@@ -713,7 +713,7 @@ void em4x50_login(uint32_t *password, bool ledcontrol) {
 }
 
 // invoke password search
-void em4x50_brute(em4x50_data_t *etd, bool ledcontrol) {
+void em4x50_brute(const em4x50_data_t *etd, bool ledcontrol) {
     em4x50_setup_read();
 
     bool bsuccess = false;
@@ -733,7 +733,7 @@ void em4x50_brute(em4x50_data_t *etd, bool ledcontrol) {
 }
 
 // check passwords from dictionary content in flash memory
-void em4x50_chk(uint8_t *filename, bool ledcontrol) {
+void em4x50_chk(const char *filename, bool ledcontrol) {
     int status = PM3_EFAILED;
     uint32_t pwd = 0x0;
 
@@ -743,11 +743,11 @@ void em4x50_chk(uint8_t *filename, bool ledcontrol) {
 
     int changed = rdv40_spiffs_lazy_mount();
     uint16_t pwd_count = 0;
-    uint32_t size = size_in_spiffs((char *)filename);
+    uint32_t size = size_in_spiffs(filename);
     pwd_count = size / 4;
     uint8_t *pwds = BigBuf_malloc(size);
 
-    rdv40_spiffs_read_as_filetype((char *)filename, pwds, size, RDV40_SPIFFS_SAFETY_SAFE);
+    rdv40_spiffs_read_as_filetype(filename, pwds, size, RDV40_SPIFFS_SAFETY_SAFE);
 
     if (changed)
         rdv40_spiffs_lazy_unmount();
@@ -873,7 +873,7 @@ static int selective_read(uint32_t addresses, uint32_t *words) {
 }
 
 // reads by using "selective read mode" -> bidirectional communication
-void em4x50_read(em4x50_data_t *etd, bool ledcontrol) {
+void em4x50_read(const em4x50_data_t *etd, bool ledcontrol) {
     int status = PM3_EFAILED;
     uint32_t words[EM4X50_NO_WORDS] = {0x0};
 
@@ -906,7 +906,7 @@ void em4x50_read(em4x50_data_t *etd, bool ledcontrol) {
 }
 
 // collects as much information as possible via selective read mode
-void em4x50_info(em4x50_data_t *etd, bool ledcontrol) {
+void em4x50_info(const em4x50_data_t *etd, bool ledcontrol) {
     int status = PM3_EFAILED;
     uint32_t words[EM4X50_NO_WORDS] = {0x0};
 
@@ -1053,7 +1053,7 @@ static int write_password(uint32_t password, uint32_t new_password) {
 // write operation process for EM4x50 tag,
 // single word is written to given address, verified by selective read operation
 // wrong password -> return with PM3_EFAILED
-void em4x50_write(em4x50_data_t *etd, bool ledcontrol) {
+void em4x50_write(const em4x50_data_t *etd, bool ledcontrol) {
     int status = PM3_EFAILED;
     uint32_t words[EM4X50_NO_WORDS] = {0x0};
 
@@ -1113,7 +1113,7 @@ void em4x50_write(em4x50_data_t *etd, bool ledcontrol) {
 }
 
 // simple change of password
-void em4x50_writepwd(em4x50_data_t *etd, bool ledcontrol) {
+void em4x50_writepwd(const em4x50_data_t *etd, bool ledcontrol) {
     int status = PM3_EFAILED;
 
     em4x50_setup_read();
@@ -1358,7 +1358,7 @@ static bool em4x50_sim_read_word(uint32_t *word) {
 }
 
 // check if reader requests receive mode (rm) by sending two zeros
-static int check_rm_request(uint32_t *tag, bool ledcontrol) {
+static int check_rm_request(const uint32_t *tag, bool ledcontrol) {
 
     // look for first zero
     int bit = em4x50_sim_read_bit();
@@ -1387,7 +1387,7 @@ static int check_rm_request(uint32_t *tag, bool ledcontrol) {
 }
 
 // send single listen window in simulation mode
-static int em4x50_sim_send_listen_window(uint32_t *tag, bool ledcontrol) {
+static int em4x50_sim_send_listen_window(const uint32_t *tag, bool ledcontrol) {
 
     SHORT_COIL();
     wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
@@ -1460,7 +1460,7 @@ static void em4x50_sim_send_nak(void) {
 }
 
 // standard read mode process (simulation mode)
-static int em4x50_sim_handle_standard_read_command(uint32_t *tag, bool ledcontrol) {
+static int em4x50_sim_handle_standard_read_command(const uint32_t *tag, bool ledcontrol) {
 
     // extract control data
     int fwr = reflect32(tag[EM4X50_CONTROL]) & 0xFF;        // first word read
@@ -1500,7 +1500,7 @@ static int em4x50_sim_handle_standard_read_command(uint32_t *tag, bool ledcontro
 }
 
 // selective read mode process (simulation mode)
-static int em4x50_sim_handle_selective_read_command(uint32_t *tag, bool ledcontrol) {
+static int em4x50_sim_handle_selective_read_command(const uint32_t *tag, bool ledcontrol) {
 
     // read password
     uint32_t address = 0;
@@ -1555,7 +1555,7 @@ static int em4x50_sim_handle_selective_read_command(uint32_t *tag, bool ledcontr
 }
 
 // login process (simulation mode)
-static int em4x50_sim_handle_login_command(uint32_t *tag, bool ledcontrol) {
+static int em4x50_sim_handle_login_command(const uint32_t *tag, bool ledcontrol) {
 
     // read password
     uint32_t password = 0;
@@ -1581,7 +1581,7 @@ static int em4x50_sim_handle_login_command(uint32_t *tag, bool ledcontrol) {
 }
 
 // reset process (simulation mode)
-static int em4x50_sim_handle_reset_command(uint32_t *tag, bool ledcontrol) {
+static int em4x50_sim_handle_reset_command(const uint32_t *tag, bool ledcontrol) {
 
     // processing pause time (corresponds to a "1" bit)
     em4x50_sim_send_bit(1);
@@ -1806,7 +1806,7 @@ void em4x50_handle_commands(int *command, uint32_t *tag, bool ledcontrol) {
 // simulate uploaded data in emulator memory
 // LED C -> reader command has been detected
 // LED D -> operations that require authentication are possible
-void em4x50_sim(uint32_t *password, bool ledcontrol) {
+void em4x50_sim(const uint32_t *password, bool ledcontrol) {
 
     int command = PM3_ENODATA;
 
diff --git a/armsrc/em4x50.h b/armsrc/em4x50.h
index af3a7a8db..eb52c36e5 100644
--- a/armsrc/em4x50.h
+++ b/armsrc/em4x50.h
@@ -21,20 +21,21 @@
 
 #include "../include/em4x50.h"
 
+// used by standalone mode
 void em4x50_setup_read(void);
 int standard_read(int *now, uint32_t *words);
-
 void em4x50_setup_sim(void);
 void em4x50_handle_commands(int *command, uint32_t *tag, bool ledcontrol);
 
-void em4x50_info(em4x50_data_t *etd, bool ledcontrol);
-void em4x50_write(em4x50_data_t *etd, bool ledcontrol);
-void em4x50_writepwd(em4x50_data_t *etd, bool ledcontrol);
-void em4x50_read(em4x50_data_t *etd, bool ledcontrol);
-void em4x50_brute(em4x50_data_t *etd, bool ledcontrol);
-void em4x50_login(uint32_t *password, bool ledcontrol);
-void em4x50_sim(uint32_t *password, bool ledcontrol);
+// dispatch functions (appmain.c)
+void em4x50_info(const em4x50_data_t *etd, bool ledcontrol);
+void em4x50_write(const em4x50_data_t *etd, bool ledcontrol);
+void em4x50_writepwd(const em4x50_data_t *etd, bool ledcontrol);
+void em4x50_read(const em4x50_data_t *etd, bool ledcontrol);
+void em4x50_brute(const em4x50_data_t *etd, bool ledcontrol);
+void em4x50_login(const uint32_t *password, bool ledcontrol);
+void em4x50_sim(const uint32_t *password, bool ledcontrol);
 void em4x50_reader(bool ledcontrol);
-void em4x50_chk(uint8_t *filename, bool ledcontrol);
+void em4x50_chk(const char *filename, bool ledcontrol);
 
 #endif /* EM4X50_H */