Text
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mruby/c: Running on Less Than
64KB RAM Microcontroller
HASUMI Hitoshi @hasumikin
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Me
HASUMI Hitoshi
@hasumikin
Live in Matsue city,
a holy place of Ruby
Sake 🍶
Soba 🍜
Coffee ☕
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Chapter 1
Introduction
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Terminology
mruby/c
A language implementation I will talk about
today
I say mrubyc since /c [slˈæʃ síː] is hard to
pronounce
Microcontroller
Small computer contains CPU, memory and
programmable I/O peripherals
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Terminology
RTOS
Real-time OS. Usually used for microcontroller
Task
Almost equivalent to `Thread` in Linux. We say
`Task` in microcontroller world
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Terminology
旭日酒造 (Asahi-Shuzo)
Shuzo means `Sake brewery`
One of the best Japanese Sake brewery
FYI, Asahi Breweries (famous for SUPER DRY)
has no concern with Asahi-Shuzo
Asahi-Shuzo and I make an IoT system using
mruby/c
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Why microcontroller?
I don't use single board computer like
Raspberry Pi for production environment.
I use microcontroller, instead
It starts immediately right after plugged in
End-users, brewery workers in my case, can
use it simply like home electical appliance
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Why microcontroller?
Microcontroller can run without OS
So-called `Bare Metal`
You can narrow security issue list
Many a malware aims at Linux or Windows
platform as a target
You don't need to consider unnecessary
deamon
You don't need to do `apt upgrade`
(RasPi can be bare metal device if you want)
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Why microcontroller?
Low energy
Rarely overheated
Many choices of power supply
Mass production
You can choose appropriate chipset (number of
GPIO, memory size, etc.) for your application
Cost advantage for parts supply and
subcontractor manufacturing
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Which microcontroller?
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Which microcontroller?
e.g. CYPRESS PSoC5LP
32 bit Arm Cortex-M3 CPU
Flash: 256KB
SRAM: 64KB (target size of mruby/c)
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Which microcontroller?
e.g. Espressif ESP-WROOM-32 (ESP32)
32 bit dual core LX6 CPU
Flash: 4MB
SRAM: 520KB
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My IoT project
IoT system for Sake brewing
PSoC5LP
Delivered to actual brew work in January
2018
Devices post temperature of Sake ingredient
in brewing, surrounding temperature and
humidity to server
Data is displayed on mobile app
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IoT in field makes you hurry
Imagine,
You have to go back and forth between dark 5℃
(=41°F) storage cellar and humid 35℃ (=95°F)
rice mold room
Brewery workers run around
You have to amend your firmware with your
small laptop in 10 minutes
You will thank Ruby's descriptiveness and
agility
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Demo
CO 2 concentration
400ppm : Atmospheric
1000ppm : Your programming speed decreases
1500ppm : FYI, tomatoes 🍅 may grow well
> 2000ppm : Sleepiness, headache
> 40000ppm : 💀
(Please look at the screen)
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Demo
My device is taking CO 2 concentration
CO 2 may increase because of your breathing
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Demo
My device is taking CO 2 concentration
CO 2 may increase because of your breathing
I will prove that it is due to CO 2 if you fell
asleep while I was speaking
😴
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Bugaboos in IoT 👻
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Bugaboos in IoT 👻
Peripheral equipments ...★
Circuit, wiring and housing
Printed circuit board = PCB
Soldering ...★
Firmware with C, mruby and mruby/c ...★
Network, TCP/IP, Bluetooth, etc.
★...I will cover these topics today
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Peripheral equipments
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Peripheral equipments
Very important to check the part before
writing application code
Do equipments like sensor or communication
module work as its spec sheets?
Whether or not the equipment is broken
(sometimes broken by soldering heat 😭)
Combining parts is unrevertable
We don't have a Git for hardware.
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Peripheral equipments
Raspberry Pi & CRuby are great for pre-
prototyping
Use breadboard or make PCB for experiment
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CRuby and serial port
# Notice: This is CRuby for RasPi
require "rubyserial"
require "timeout"
sp = Serial.new "/dev/serial0", 9600, 8
loop do
puts "[command]"
command = gets
sp.write command.sub("\n", "\r") # replace LF if needed
sleep 0.1
result = ""
begin
Timeout.timeout(10) do
loop do
line = sp.read(128)
break if line == "" && result != ""
result << line
sleep 0.1
end
puts "=> " + result
end
rescue Timeout::Error
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CRuby and serial port
$ serial_communication_test.rb
[command]
AT
# command
=> OK
# response
[command]
AT+CIMI
# command
=> 123456789012 # response
[command]
AT+XXX
# command
=> error
# response
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Soldering
It often works even if you leave a pin
unsoldered on surface mounting
Because the pin touches circuit's plate
Then, it will come not to work one day
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Soldering
Discovering this kind of bug is much more
difficult than software bug
My teacher said "All the cause of failure, it is
impatience"
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Chapter 2
mruby/c
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What is mruby?
github.com/mruby/mruby
Another implemantation of Ruby for general
embedded usage
Easily combined with system programming
like C/C++
e.g. ngx_mruby is a popular product of
mruby
Good for making command line tool as one-
binary executable
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What is mruby/c?
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What is mruby/c?
github.com/mrubyc/mrubyc
Yet another implementation of mruby
`/c` symbolizes compact, concurrent and
capability
Especially dedicated to one-chip
microcontroller
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Bytecode is a common stuff
They are compiled by `mrbc` (mruby compiler)
and each VM execute bytecode
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Bytecode?
A kind of intermediate representation
mruby bytecode is designed for mruby VM
mruby VM dynamically interprets the
bytecode and processes the application
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HEX dump of bytecode
Looks like this if you compile
`puts "Hello World!"`
5249
545a
3032
1001
0000
0000
0008
5445
3030
0000
4f02
0c48
0100
3030
3030
0060
002e
656c
0470
3036
4952
0001
0100
6c6f
7574
9a78
4550
0004
0137
2057
7300
0000
0000
0000
0167
6f72
454e
0062
0044
0000
0000
6c64
4400
4d41
3030
000c
0001
2100
0000
RITE0006.x...bMA
TZ0000IREP...D00
02...`..........
..O......7.g....
...Hello World!.
.....puts.END...
..
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mruby on microcontroller
RTOS (Real-Time OS) manages mruby VMs in
order to realize multi tasking
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mruby/c on microcontroller
mruby/c has its own mechanism to manage
multi tasks: rrt0
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mruby and mruby/c
mruby
mruby/c
v1.0.0 in Jan 2014 v1.0 in Jan 2017
for general
embedded software for one-chip
microcontroller
mrbgems no package manager
RAM < 200KB ...(*) RAM < 40KB ...(*)
(*)...It depends on the situation
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mruby/c's Virtual Machine
Much smaller than mruby's one
That's why mruby/c runs on smaller RAM
Accordingly, mruby/c has less functionality
than mruby and CRuby
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How less? - For example
mruby/c doesn't have module, hence there
is no Kernel module
Then you must wonder how can you `#puts`?
In mruby/c, `#puts` is implemented in Object
class
mruby/c doesn't have #send, #eval, and
#method_missing, etc.
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How less? - For example
The full list of mruby/c's classes
Array, FalseClass, Fixnum, Float, Hash,
Math, Mutex, NilClass, Numeric, Object,
Proc, Range, String, Symbol, TrueClass, VM
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Despite the fact,
No problem in practical usage of
microcontroller
As far as IoT goes, mruby/c is enough Ruby
We can fully develop firmwares with these
features of mruby/c
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How does mruby/c work
~/project/sample_project
├─ main.c
├─ mrblib
│ ├─ task_1.rb
│ └─ task_2.rb
└─ src
├─ task_1.c
└─ task_2.c
task_*.c is compliled bytecode from
task_*.rb
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How does mruby/c work
/* main.c */
#include "src/task_1.c"
#include "src/task_2.c"
// using 40KB RAM for VM heap in this case
#define MEMORY_SIZE (1024 * 40)
static uint8_t memory_pool[MEMORY_SIZE];
int main(void) {
mrbc_init(memory_pool, MEMORY_SIZE);
mrbc_create_task(task_1, 0);
mrbc_create_task(task_2, 0);
mrbc_run(); // 2 tasks run concurrently!
return 0;
}
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How does mruby/c work
We can run easily multiple VMs with
concurrency feature of rrt0
You might be disappointed to know you
have to write C
Yes, we have to write main.c
Don't worry, it's almost boilerplate code
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Chapter 3
Application code
and tools
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Application code
github.com/hasumikin/co2_demo
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Application code
~/project/co2_demo
├─ main.c
└─ mrblib
├─ loops
│ ├─ primary.rb
│ └─ secondary.rb
└─ models
├─ co2.rb
├─ led.rb
└─ thermistor.rb
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Application code
# loops/primary.rb
$co2 = Co2.new
# Makes it global so that secondary task can use it
$thermistor = $thermistor.new
led = Led.new(19) # 19 is a pin number which LED connects
while true
co2 = $co2.concentrate
if co2 > 2000
# When CO2 reaches fatal level
5.times do
# Turning LED on and off
led.turn_on
sleep 0.1
led.turn_off
sleep 0.1
end
else
# Safe level
led.turn_off # Turns off
sleep 1
end
end
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Application code
How does Led#trun_on work?
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Application code
# models/led.rb
class Led
def initialize(pin)
@pin = pin
gpio_init_output(@pin)
turn_off
end
def turn_on
gpio_set_level(@pin, 1) # high
end
def turn_off
gpio_set_level(@pin, 0) # low
end
end
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Application code
/* a part of main.c */
#include "models/led.c"
static void c_gpio_init_output(mrbc_vm *vm, mrbc_value *v, int argc) {
int pin = GET_INT_ARG(1);
// Function of microcontroller's library
gpio_set_direction(pin, GPIO_MODE_OUTPUT);
}
static void c_gpio_set_level(mrbc_vm *vm, mrbc_value *v, int argc){
int pin = GET_INT_ARG(1);
int level = GET_INT_ARG(2);
gpio_set_level(pin, level); // Function of microcontroller's library
}
int main(void){
...
mrbc_define_method(0, mrbc_class_object, "gpio_init_output",
c_gpio_init_output);
mrbc_define_method(0, mrbc_class_object, "gpio_set_level",
c_gpio_set_level);
...
}
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Application code
/* a part of main.c */
#include "models/co2.c"
static void c_get_co2(struct VM *vm, mrbc_value v[], int argc){
uint8_t command[] = { // Command to take CO2
0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79
};
uart_write_bytes(uart_num, (const char*)command, 9);
// ↑Write then ↓Read data
uint8_t data[10];
int length = 0;
length = uart_read_bytes(uart_num, data, length, 10);
mrbc_value array = mrbc_array_new( vm, 9 ); // mrubyc's variable
for( int i = 0; i < 9; i++ ) {
mrbc_value value = mrbc_fixnum_value(data[i]);
mrbc_array_set( &array, i, &value ); // Adding a value to array
}
SET_RETURN(array); // Returning the array object to mruby
}
int main(void){
...
mrbc_define_method(0, mrbc_class_object, "get_co2", c_get_co2);
...
}
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Application code
# models/co2.rb
class Co2
def concentrate
res = get_co2
# checks if the sensor works
if res[0] == 255 && res[1] == 134
res[2] * 256 + res[3]
else
0
end
end
end
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Application code
Trivial tip to reduce memory usage
C function can return String instead of Array
`mrbc_array_new` will allocate larger memory
than `mrbc_string_new`
So, you can use String instead of Array if
memory becomes short
Remember STRING of C is just an array of char
and '\0'
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Application code
# loops/secondary.rb
http_client = HttpClient.new("http://data.server")
while true
co2 = $co2.concentrate
temperature = $thermistor.temperature
if co2 > 0 # No trouble
data = "co2=#{co2}&temperature=#{temperature}"
http_client.post(data)
sleep 180
else
# A trouble happens?
sleep 3 # Or you can retry
end
end
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Dev tools for mruby/c
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Dev tools for mruby/c
mrubyc-utils
mrubyc-test
mrubyc-debugger
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Dev tools for mruby/c
I am trying to make mruby/c development
Rubyish
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Rubyish? - IMHO
Unix/Linux
Command line
No-IDE (as far as possible)
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Rubyish? - IMHO
Unix/Linux
Command line
No-IDE (as far as possible)
Taking full advantage of
our Laptop and Ruby World
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mrubyc-utils
github.com/hasumikin/mrubyc-utils
One-binary tool made with mruby
Helps to install boilerplate of application
Utility subcommands like...
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mrubyc-utils
$
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
mrubyc-utils classes
Array
FalseClass
Fixnum
Float
Hash
Math
Mutex
NilClass
Numeric
Object
Proc
Range
String
Symbol
TrueClass
VM
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mrubyc-utils
$ mrubyc-utils methods
Array
- +
- <<
- []
- []=
- at
- clear
- collect
- collect!
- count
- delete_at
- dup
- each
- each_index
- each_with_index
- empty?
- first
- index
--class=array
-
-
-
-
-
-
-
-
-
-
-
-
-
-
inspect
join
last
length
max
min
minmax
new
pop
push
shift
size
to_s
unshift
< Object
- !
...
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mrubyc-test
github.com/mrubyc/mrubyc-test
Unit testing framework
A RubyGem implemented with CRuby
Supports stub and mock
Official test tool of mruby/c dev team
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mrubyc-test
Gathers information from app and test code
Internally generates stub and mock methods
Makes all-in-one script: test.rb
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mrubyc-debugger
github.com/hasumikin/mrubyc-debugger
Debugger for mutiple infinite loops
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DEMO
github.com/hasumikin/
mrubyc-debugger
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DEMO
How is CO 2 going?
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DEMO (added after the Conf)
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Conclusion
You should
refresh air 💨
