diff --git a/src/Makefile b/src/Makefile
index 7e5c748..61b5f90 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -75,7 +75,7 @@ ASRC = startup.S crc.S
 #     (Note: 3 is not always the best optimization level. See avr-libc FAQ.)
 # Use s -mcall-prologues when you really need size...
 #OPT = 2
-OPT = 2
+OPT = s
 
 # Debugging format.
 DEBUG = dwarf-2
diff --git a/src/cli.c b/src/cli.c
index d5d6852..7e8d78c 100644
--- a/src/cli.c
+++ b/src/cli.c
@@ -138,7 +138,7 @@ static int8_t parse_wordlist(char *wordlist) {
         return -1;
       }
 
-      if (tolower(c) != tolower(*cur)) {
+      if (tolower((int)c) != tolower((int)*cur)) {
         // Check for end-of-word
         if (cur != curchar && (*cur == ' ' || *cur == 0)) {
           // Partial match found, return that
diff --git a/src/filetypes.c b/src/filetypes.c
index c691427..6df3d5a 100644
--- a/src/filetypes.c
+++ b/src/filetypes.c
@@ -65,7 +65,7 @@ uint32_t scan_dir(char* path, FILINFO* fno_param, char mkdb, uint32_t this_dir_t
   static uint32_t next_subdir_tgt;
   static uint32_t parent_tgt;
   static uint32_t dir_end = 0;
-  static uint8_t was_empty = 0;
+/*  static uint8_t was_empty = 0;*/
   static uint16_t num_files_total = 0;
   static uint16_t num_dirs_total = 0;
   uint32_t dir_tgt;
@@ -147,7 +147,7 @@ uint32_t scan_dir(char* path, FILINFO* fno_param, char mkdb, uint32_t this_dir_t
         res = f_readdir(&dir, &fno);
         if (res != FR_OK || fno.fname[0] == 0) {
           if(pass) {
-            if(!numentries) was_empty=1;
+/*            if(!numentries) was_empty=1;*/
           }
           break;
         }
@@ -194,7 +194,7 @@ uint32_t scan_dir(char* path, FILINFO* fno_param, char mkdb, uint32_t this_dir_t
                 sram_writeblock("/\0", old_db_tgt + sizeof(next_subdir_tgt) + sizeof(len) + pathlen, 2);
               }
               dir_tgt += 4;
-              was_empty = 0;
+/*              was_empty = 0;*/
             } else if(!mkdb) {
               path[len]='/';
               strncpy(path+len+1, (char*)fn, sizeof(fs_path)-len);
diff --git a/src/memory.c b/src/memory.c
index 8dd2049..5530b3f 100644
--- a/src/memory.c
+++ b/src/memory.c
@@ -473,7 +473,6 @@ uint32_t load_bootrle(uint32_t base_addr) {
 
 void save_sram(uint8_t* filename, uint32_t sram_size, uint32_t base_addr) {
   uint32_t count = 0;
-  uint32_t num = 0;
 
   FPGA_DESELECT();
   file_open(filename, FA_CREATE_ALWAYS | FA_WRITE);
@@ -490,7 +489,7 @@ void save_sram(uint8_t* filename, uint32_t sram_size, uint32_t base_addr) {
       count++;
     }
     FPGA_DESELECT();
-    num = file_write();
+    file_write();
     if(file_res) {
       uart_putc(0x30+file_res);
     }
@@ -594,7 +593,6 @@ uint64_t sram_gettime(uint32_t base_addr) {
 
 void load_dspx(const uint8_t *filename, uint8_t coretype) {
   UINT bytes_read;
-  DWORD filesize;
   uint16_t word_cnt;
   uint8_t wordsize_cnt = 0;
   uint16_t sector_remaining = 0;
@@ -618,7 +616,6 @@ void load_dspx(const uint8_t *filename, uint8_t coretype) {
   }
 
   file_open((uint8_t*)filename, FA_READ);
-  filesize = file_handle.fsize;
   if(file_res) {
     printf("Could not read %s: error %d\n", filename, file_res);
     return;
diff --git a/src/msu1.c b/src/msu1.c
index 3207b62..5e663a3 100644
--- a/src/msu1.c
+++ b/src/msu1.c
@@ -204,15 +204,12 @@ int msu1_loop() {
     /* Data buffer refill */
     if((fpga_status_now & 0x2000) != (fpga_status_prev & 0x2000)) {
       DBG_MSU1 printf("data\n");
-      uint8_t pageno = 0;
       if(fpga_status_now & 0x2000) {
         msu_addr = 0x0;
         msu_page1_start = msu_page2_start + msu_page_size;
-        pageno = 1;
       } else {
         msu_addr = 0x2000;
         msu_page2_start = msu_page1_start + msu_page_size;
-        pageno = 2;
       }
       set_msu_addr(msu_addr);
       sd_offload_tgt=2;
diff --git a/src/xmodem.c b/src/xmodem.c
index 979f8d4..83f2398 100644
--- a/src/xmodem.c
+++ b/src/xmodem.c
@@ -6,8 +6,8 @@
 #include "xmodem.h"
 
 void xmodem_rxfile(FIL* fil) {
-  uint8_t rxbuf[XMODEM_BLKSIZE], sum=0, sender_sum;
-  uint8_t blknum, blknum2;
+  uint8_t rxbuf[XMODEM_BLKSIZE], sum=0/*, sender_sum*/;
+/*  uint8_t blknum, blknum2;*/
   uint8_t count;
   uint32_t totalbytes = 0;
   uint32_t totalwritten = 0;
@@ -19,13 +19,13 @@ void xmodem_rxfile(FIL* fil) {
     uart_putc(ASC_NAK);
   } while (uart_getc() != ASC_SOH);
   do {
-    blknum=uart_getc();
-    blknum2=uart_getc();
+    /*blknum=*/uart_getc();
+    /*blknum2=*/uart_getc();
     for(count=0; count<XMODEM_BLKSIZE; count++) {
       sum += rxbuf[count] = uart_getc();
       totalbytes++;
     }
-    sender_sum = uart_getc();
+    /*sender_sum =*/ uart_getc();
     res=f_write(fil, rxbuf, XMODEM_BLKSIZE, &written);
     totalwritten += written;
     uart_putc(ASC_ACK);