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+How to use SIS with GDB
+-----------------------
+
+1. Building GDB with SIS
+
+To build GDB with the SIS/ERC32 simulator, configure with option
+'--target sparc-erc32-aout' and build as usual.
+
+2. Attaching the simulator
+
+To attach GDB to the simulator, use:
+
+target sim [options] [files]
+
+The following options are supported:
+
+ -nfp		Disable FPU. FPops will cause an FPU disabled trap.
+
+ -freq <f>	Set the simulated "system clock" to <f> MHz.
+
+ -v		Verbose mode.
+
+ -nogdb		Disable GDB breakpoint handling (see below)
+
+The listed [files] are expected to be in aout format and will be
+loaded in the simulator memory prior. This could be used to load
+a boot block at address 0x0 if the application is linked to run
+from RAM (0x2000000).
+
+To start debugging a program type 'load <program>' and debug as
+usual. 
+
+The native simulator commands can be reached using the GDB 'sim'
+command:
+
+sim <sis_command>
+
+Direct simulator commands during a GDB session must be issued
+with care not to disturb GDB's operation ... 
+
+For info on supported ERC32 functionality, see README.sis.
+
+
+3. Loading aout files
+
+The GDB load command loads an aout file into the simulator
+memory with the data section starting directly after the text
+section regardless of wich start address was specified for the data
+at link time! This means that your applications either has to include
+a routine that initialise the data segment at the proper address or
+link with the data placed directly after the text section.
+
+A copying routine is fairly simple, just copy all data between
+_etext and _data to a memory loaction starting at _environ. This
+should be done at the same time as the bss is cleared (in srt0.s).
+
+
+4. GDB breakpoint handling
+
+GDB inserts breakpoint in the form of the 'ta 1' instruction. The
+GDB-integrated simulator will therefore recognize the breakpoint
+instruction and return control to GDB. If the application uses
+'ta 1', the breakpoint detection can be disabled with the -nogdb
+switch. In this case however, GDB breakpoints will not work.
+
+
+Report problems to Jiri Gaisler ESA/ESTEC (jgais@wd.estec.esa.nl)