esp8266/makeimg.py: Print out info about RAM segments when building fw.

ports/esp8266/makeimg.py

@@ -2,6 +2,11 @@ import sys
 import struct
 import hashlib
 
+# This region at the start of flash contains a small header and then segments
+# containing .text, .data and .rodata, and so must be large enough to hold all
+# of this.  This data is loaded to the appropriate places in RAM by the ROM
+# bootloader at boot.  After this in flash comes .irom0.text, which must begin
+# on a flash erase-page boundary.
 SEGS_MAX_SIZE = 0x9000
 
 assert len(sys.argv) == 4
@@ -18,6 +23,15 @@ with open(sys.argv[3], "wb") as fout:
         md5.update(data_flash[4:])
         print("flash    ", len(data_flash))
 
+        # Print info about segments in this first part of flash
+        num_segs = struct.unpack_from("<BBBBI", data_flash, 0)[1]
+        offset = 8
+        for seg_num in range(num_segs):
+            seg_name = [".text", ".data", ".rodata"][seg_num]
+            seg_offset, seg_size = struct.unpack_from("<II", data_flash, offset)
+            print(" {:7}  {} at 0x{:x}".format(seg_name, seg_size, seg_offset))
+            offset += 8 + seg_size
+
     with open(sys.argv[2], "rb") as f:
         data_rom = f.read()