Configuring Emu68
Since Emu68 JIT is not aware of surrounding hardware or peripherals attached to the machine (with only few exceptions) the configuration can be done only through the command line parameters. These can be set through the cmdline.txt
file placed on the boot FAT32 partition together with Emu68.img file.
Options in cmdline.txt
The cmdline.txt is a one-line file which is passed directly into the device tree available on the M68k through a resource. It can be found in the bootargs
property of the /chosen
node like in the following example:
// The prototypes for devicetree.resource
#include <proto/devicetree.h>
APTR DeviceTreeBase = OpenResource("devicetree.resource");
/* Open /chosen node */
APTR key = DT_OpenKey("/chosen");
if (key)
{
APTR property = DT_FindProperty(key, "bootargs");
if (property)
{
CONST_STRPTR bootargs = DT_GetPropValue(property);
ULONG bootargs_len = DT_GetPropLen(property);
/*
Now bootargs points to a **NOT** terminated character sequence which can be
searched for any necessary parameter.
*/
[...]
}
DT_CloseKey(key);
}
Below are currently implemented options, grouped by the affected modules and/or functionalities.
brcm-sdhc.device
sd.verbose=0 | 1 | 2
Adjust verbosity of the driver. Value0
is default one and it shuts off debug nearly completely. Value1
gives some more details from the driver, whereas value2
should be used only for debugging purposes since it reports every single BeginIO call.sd.unit0=off | ro | rw
Change the behaviour of sdhc-brcm.device unit 0. Default value isro
which means the unit is not hidden, but cannot be written to. Changing the value tooff
disables the unit 0 completely whereasrw
allows one to write data to it. Use with care, as Unit 0 of the device represents the entire card, including partition table and FAT32 boot partition.sd.low_speed
Disables 50 MHz clock even if the microSD card reports that the clock is supported. Setting this option disables SD card overclocking (see subsequent option).sd.clock=num
Selects the clock speed in MHz which will be switched on instead of default 50 MHz if the card supports the high-speed mode. The option has no effect ifsd.low_speed
was also applied.
68040.library
vbr_move
Moves VBR (base address for exception vector table) from CHIP to FAST ram. This setting improves the performance slightly, since the FAST ram on Emu68 is at least 500 times faster than CHIP, but reduces compatibility with old games and demos started from floppy drive drastically. However, system-friendly software as well as demos and games started through WHDLoad should not be affected.
emu68-vc4.card
vc4.mem=num
Sets size of VC4 memory reported to P96 subsystem tonum
MB. Default is 16 in case of PiStorm build and 0 in all other Emu68 variants. Please note this is not the same asgpu_mem
setting in config.txt file. The latter is used to assign general purpose memory to the VPU.
Debugging
debug
Enables debugging of the JIT engine. Every portion of m68k code translated to AArch64 will be shown in form of short statistics and binary dump of ARM code. Statistics include number of m68k instructions translated, resulting number of ARM instructions, mean ARM instruction number per m68k opcode and CRC32 checksum of translated memory block.disassemble
Shows disassembled blocks in two columns. The left column contains m68k code disassembly whereas the right column is the AArch64 code. The two are aligned vertically so that the translated code can be assigned to every single m68k opcode properly.async_log
Use asynchronous log on separate ARM core with a 8 MB large ring buffer. Improves performance of m68k when debug is enabled.fast_serial
Use synchronous serial port running at a speed varying between 10 and 50 MBit instead of regular serial protocol at 921.6 kBit. Requires proper hardware such as e.g. FT232H.
Memory
limit_2g
Limit the mapped ARM memory to two gigabytes. Useful on machines which offer more RAM and, because of that, confuse e.g. AmigaOS.enable_c0_slow
Enables “slow” memory in0xc00000...0xc7ffff
range.enable_c8_slow
Enables “slow” memory in0xc80000...0xcfffff
range. Requiresenable_c0_slow
.enable_d0_slow
Enables “slow” memory in0xd00000...0xd7ffff
range. Requiresenable_c0_slow
andenable_c8_slow
activated.move_slow_to_chip
Maps 512K memory expansion of A500 to the CHIP ram range.z2_ram_size=0 | 1 | 2 | 4 | 8
Set size of Zorro II RAM expansion to 0 to 8 MB. Default is 8, but eventually has to be lowered if other Zorro II devices are installed in the system.
Miscellaneous
enable_cache
Turns on JIT cache inCACR
register on startup. Useful in case of bare metal software started instead of AROS or AmigaOS ROM.nofpu
Disables the FPU unit of Emu68. All LineF opcodes related to FPU will trigger the exception.swap_df0_with_df1
Swaps DF0 with DF1 floppy drive.swap_df0_with_df2
Swaps DF0 with DF2 floppy drive.swap_df0_with_df3
Swaps DF0 with DF3 floppy drive.