Update README.

[fw/stlink] / README

diff --git a/README b/README
index 77697c89b50864c19b9a2669f1ef42215c1567d9..c94177bac1714011fc1926386e9254c94260c4fb 100644 (file)
--- a/README
+++ b/README
@@ -1,8 +1,8 @@
 HOWTO
 =====
 
-To run the gdb server, do (you do not need sudo if you have
-set up permissions correctly):
+To run the gdb server, do (you do not need sudo if you have set up
+permissions correctly):
 $ make -C build && sudo ./build/st-util 1234 /dev/sg1
 
 Then, in gdb:
@@ -10,9 +10,38 @@ Then, in gdb:
 
 Have fun!
 
-Caveats
-=======
+Running programs from SRAM
+==========================
 
-`continue' GDB command does not work: target does not step at
-all or steps with a turtle speed. Looks like there's something
-wrong with SCSI requests.
+You can run your firmware directly from SRAM if you want to. Just link
+it at 0x20000000 and do
+(gdb) load firmware.elf
+
+It will be loaded, and pc will be adjusted to point to start of the
+code, if it is linked correctly (i.e. ELF has correct entry point).
+
+Writing to flash
+================
+
+The GDB stub ships with a correct memory map, including the flash area.
+If you would link your executable to 0x08000000 and then do
+(gdb) load firmware.elf
+then it would be written to the memory.
+
+FAQ
+===
+
+Q: My breakpoints do not work at all or only work once.
+
+A: Optimizations can cause severe instruction reordering. For example,
+if you are doing something like `REG = 0x100;' in a loop, the code may
+be split into two parts: loading 0x100 into some intermediate register
+and moving that value to REG. When you set up a breakpoint, GDB will
+hook to the first instruction, which may be called only once if there are
+enough unused registers. In my experience, -O3 causes that frequently.
+
+Q: At some point I use GDB command `next', and it hangs.
+
+A: Sometimes when you will try to use GDB `next' command to skip a loop,
+it will use a rather inefficient single-stepping way of doing that.
+Set up a breakpoint manually in that case and do `continue'.