Cartesi's reference off-chain implementation of Cartesi Machines is based on software emulation. The emulator is written in C/C++ with POSIX dependencies restricted to the terminal, process, and memory-mapping facilities. It is written as a C++ library, but can be accessed in a variety of different ways.

When linked to a C++ application, the emulator can be controlled directly via the interface of the cartesi::machine class. The emulator can also be accessed from the Lua programming language, via a cartesi module that exposes a cartesi.machine interface to Lua programs, mirroring the C++ interface. Additionally, Cartesi provides a gRPC server that can be run to control a Cartesi Machine instance remotely. This server exposes a higher-level interface better suited for the verification process, including the ability to create in-memory snapshots of the current machine state so that later modifications can be rolled back. Finally, there is a command-line utility (written in Lua) that can configure and run Cartesi Machines for rapid prototyping. The emulator/ directory in the Emulator SDK can be used to build and install the Cartesi Machine emulator. The emulator can then be used via any of these methods.

The documentation starts from the command-line utility, cartesi-machine. This utility is used for most prototyping tasks. The documentation then covers the Lua interface of cartesi.machine. The C++ interface is very similar, and is covered only within its reference manual. The same is true of the gRPC interface, used to control an emulator remotely.

What's in a machine

Cartesi Machines are separated into a processor and a board. The processor performs the computations, executing the traditional fetch-execute loop while maintaining a variety of registers. The board defines the surrounding environment with an assortment of memories (ROM, RAM, flash drives) and a number of devices. Memories and devices are mapped to the 64-bit physical address space of the Cartesi Machine. The amount of RAM, as well as the number, length, and position of the flash drives in the address space can be chosen according to the needs of each particular application.

In a typical scenario, a Cartesi Machine is initialized and then run until it halts. At a minimum, the initialization process loads a ROM image, a RAM image, and a root file-system (as a flash drive) from regular files in the host file-system. Execution starts from the ROM image, which contains a simple program that creates a description of the machine organization for the Linux kernel. The ROM image rom.bin can be built in the rom/ directory in the Emulator SDK. The Linux kernel itself resides in the RAM image linux.bin, built in the kernel/ directory in the Emulator SDK. After it is done with its own initialization, the Linux kernel cedes control to the /sbin/init program in the root file-system. The root file-system rootfs.ext2 contains all the data files and programs that make up an embedded Linux distribution. It can be built in the fs/ directory in the Emulator SDK. The DApp components can reside in the root file-system itself, or in their own, separate file-system. Additional flash drives can be used as the DApp input and output, either containing file-systems or containing raw data. The emulator can be instructed to execute whatever computation the DApp wishes to perform inside the Cartesi Machine. For a complete description of the Cartesi Machine architecture and the boot process, see the documentation for the target perspective.

Machine playground

The setup of a new development environment is often a time-consuming task. This is particularly true in case of cross-development environments (i.e., when the development happens in a host platform but software runs in a different target platform). With this in mind, the Cartesi team provides the cartesi/playground Docker image, which enables immediate experimentation with Cartesi Machines. This comes with a pre-built emulator and Lua interpreter accessible within the command-line, as well as a pre-built ROM image, RAM image, and root file-system. It also comes with the cross-compiler for the RISC-V architecture on which the Cartesi Machine is based.

To enter the playground, open a terminal, download the Docker image from Cartesi's repository, and run it adequately mapping the current user and group information, as well as making the host's current directory available inside the container:

$ docker pull cartesi/playground:0.3.0
$ docker run -it --rm -h playground \
-e USER=$(id -u -n) \
-e GROUP=$(id -g -n) \
-e UID=$(id -u) \
-e GID=$(id -g) \
-v `pwd`:/home/$(id -u -n) \
-w /home/$(id -u -n) \
cartesi/playground:0.3.0 /bin/bash

Once inside, you can execute the cartesi-machine utility as follows:

playground:~$ cartesi-machine --help
/opt/cartesi/bin/cartesi-machine.lua [options] [command] [arguments]
where options are:
address of the remote cartesi machine server in one of the following
name of file containing RAM image (default: "linux.bin")
forget settings for RAM image
set RAM length
name of file containing ROM image (default: "rom.bin")
clear default bootargs
append <string> to bootargs
clear default root flash drive and associated bootargs parameters
defines a new flash drive, or modify an existing flash drive definition
flash drives appear as /dev/mtdblock[1-7]
<key>:<value> is one of
label (mandatory)
identifies the flash drive and init attempts to mount it as /mnt/<label>
filename (optional)
gives the name of the file containing the image for the flash drive
when omitted or set to the empty string, the drive starts filled with 0
start (optional)
sets the starting physical memory offset for flash drive in bytes
when omitted, drives start at 2 << 63 and are spaced by 2 << 60
if any start offset is set, all of them must be set
length (optional)
gives the length of the flash drive in bytes (must be a multiple of 4Ki)
if omitted, the length is computed from the image in filename
if length and filename are set, the image file size must match length
shared (optional)
target modifications to flash drive modify image file as well
by default, image files are not modified and changes are lost
(an option "--flash-drive=label:root,filename:rootfs.ext2" is implicit)
replaces an existing flash drive right after machine instantiation.
(typically used in conjunction with the --load=<directory> option.)
<key>:<value> is one of
semantics are the same as for the --flash-drive option with the following
difference: start and length are mandatory, and must match those of a
previously existing flash drive.
configures the dehashing device
by default, the device is not present
<key>:<value> is one of
filename (optional)
gives the name of the file containing the initial dehashed data.
when omitted or set to the empty string, the data starts filled with 0
tstart (mandatory when device present)
sets the start of target physical memory range for output data
must be aligned to tlength
tlength (mandatory when device present)
gives the length of target physical memory range for output data
must be a power of 2 greater than 4Ki, or 0 when device not present
server acting as source for dehashed data
stop at a given mcycle (default: 2305843009213693952)
-i or --htif-console-getchar
run in interactive mode
honor yield progress requests by target
honor yield rollup requests by target
dump initial machine config to screen
load prebuilt machine from <directory>
store machine to <directory>
print initial state hash before running machine
print final state hash when done
prints root hash every <number-period> cycles. If <number-start> is given,
the periodic hashing will start at that mcycle. This option implies
--initial-hash and --final-hash.
(default: none)
print step log for 1 additional cycle when done
output json with step logs for all cycles to <filename>
dump all PMA ranges to disk when done
and command and arguments:
the full path to the program inside the target system
(default: /bin/sh)
the given command arguments
<number> can be specified in decimal (e.g., 16) or hexadeximal (e.g., 0x10),
with a suffix multiplier (i.e., Ki, Mi, Gi for 2^10, 2^20, 2^30, respectively),
or a left shift (e.g., 2 << 20).
<host> can be a host name, IPv4 or IPv6 address.

A final check can also be performed to verify if the contents inside the container are as expected:

playground:~$ md5sum /opt/cartesi/share/images/linux.bin
f7b127f9daba80d447df5656f911dfdd /opt/cartesi/share/images/linux.bin
playground:~$ md5sum /opt/cartesi/share/images/rom.bin
ff7df0dc89a60e0da0501b29b3700111 /opt/cartesi/share/images/rom.bin
playground:~$ md5sum /opt/cartesi/share/images/rootfs.ext2
f0d8d44543c78000c8906ed20a79e91f /opt/cartesi/share/images/rootfs.ext2