Runtime (crt0)

By default, when using my link scripts, the standard runtime is initialised by crt0 as follows:

Address	Size	Variable Name	Comment
`0x03fffe`	~256k	`_STACK_SIZE`	Stack (SSP). Grows towards 0. At round about 0x0000400 it would start stomping all over the memory area used by the monitor
`0x040000`	n/a	`_RUN_ADDRESS`	Start of user program (.text), followed by initialised data (.data) and then unititialised data (.bss).

You can override the values at link time by using the linker option:

--defsym=<Variable Name>=<value>

You can use this option as many times as needed.

Before calling main()

If the code is running in ROM, a banner message will be printed, similar to the following:

Mega-680x0 Computer System
Code is running in ROM
68030 Processor running at ~40MHz

All free memory from the end of the .bss area to the end of ram to the heap (malloc/free).

crt0 sets the following global variables:

Variable	Comment
uint8_t cpu_speed_mhz.	This uses the counter in the PI/T to figure out roughly how fast the CPU is being clocked at. Within a MHz or so.
uint8_t cpu_type.	Figures out what CPU is installed: 0 - 68000/68008, 1 - 68010, 2 - 68020, 3 - 68030
uint8_t running_in_rom.	When non-zero, indicates that the code is running in ROM. 0 indicates it's running in RAM.

To access any of these variables, simply #include <machine.h.>

When main() returns or when exit() is called, a non-zero exit code will be displayed as follows:

exited with status: <value>

No message is printed if the exit code was zero. Control will then be passed back to the monitor