diff --git a/toolbox/r.c b/toolbox/r.c
index 5a82e20..eb8ea0b 100644
--- a/toolbox/r.c
+++ b/toolbox/r.c
@@ -13,8 +13,10 @@
 int r_main(int argc, char *argv[])
 {
     int width = 4, set = 0, fd;
-    unsigned addr, value;
+    unsigned addr, value, endaddr = 0;
+    unsigned long mmap_start, mmap_size;
     void *page;
+    char *end;
     
     if(argc < 2) return usage();
 
@@ -31,6 +33,18 @@
     if(argc < 2) return usage();
     addr = strtoul(argv[1], 0, 16);
 
+    end = strchr(argv[1], '-');
+    if (end)
+        endaddr = strtoul(end + 1, 0, 16);
+
+    if (!endaddr)
+        endaddr = addr + width - 1;
+
+    if (endaddr <= addr) {
+        fprintf(stderr, "invalid end address\n");
+        return -1;
+    }
+
     if(argc > 2) {
         set = 1;
         value = strtoul(argv[2], 0, 16);
@@ -42,33 +56,40 @@
         return -1;
     }
     
-    page = mmap(0, 8192, PROT_READ | PROT_WRITE,
-                MAP_SHARED, fd, addr & (~4095));
+    mmap_start = addr & ~(PAGE_SIZE - 1);
+    mmap_size = endaddr - mmap_start + 1;
+    mmap_size = (mmap_size + PAGE_SIZE - 1) & ~(PAGE_SIZE - 1);
+
+    page = mmap(0, mmap_size, PROT_READ | PROT_WRITE,
+                MAP_SHARED, fd, mmap_start);
 
     if(page == MAP_FAILED){
         fprintf(stderr,"cannot mmap region\n");
         return -1;
     }
 
-    switch(width){
-    case 4: {
-        unsigned *x = (unsigned*) (((unsigned) page) + (addr & 4095));
-        if(set) *x = value;
-        fprintf(stderr,"%08x: %08x\n", addr, *x);
-        break;
+    while (addr <= endaddr) {
+        switch(width){
+        case 4: {
+            unsigned *x = (unsigned*) (((unsigned) page) + (addr & 4095));
+            if(set) *x = value;
+            fprintf(stderr,"%08x: %08x\n", addr, *x);
+            break;
+        }
+        case 2: {
+            unsigned short *x = (unsigned short*) (((unsigned) page) + (addr & 4095));
+            if(set) *x = value;
+            fprintf(stderr,"%08x: %04x\n", addr, *x);
+            break;
+        }
+        case 1: {
+            unsigned char *x = (unsigned char*) (((unsigned) page) + (addr & 4095));
+            if(set) *x = value;
+            fprintf(stderr,"%08x: %02x\n", addr, *x);
+            break;
+        }
+        }
+        addr += width;
     }
-    case 2: {
-        unsigned short *x = (unsigned short*) (((unsigned) page) + (addr & 4095));
-        if(set) *x = value;
-        fprintf(stderr,"%08x: %04x\n", addr, *x);
-        break;
-    }
-    case 1: {
-        unsigned char *x = (unsigned char*) (((unsigned) page) + (addr & 4095));
-        if(set) *x = value;
-        fprintf(stderr,"%08x: %02x\n", addr, *x);
-        break;
-    }
-    }    
     return 0;
 }