mruby can be more lightweight(en)

1. mruby can be more
lightweight
2018-06-01 RubyKaigi 2018
Yurie Yamane
Team Yamanekko

2. About me
• yurie yamane
• Team yamanekko
• GitHub: https://github.com/yamanekko
• Qiita: https://qiita.com/yamanekko
• a member of Toppers project
• a staff of SWEST
(Summer Workshop on Embedded System Technologies)
https://swest.toppers.jp/
TOPAME
matz

3. About me
• smaller mruby
• low cost microcomputer
• IDE for mruby(VS Code)
• porting nomitory to VS Code
• DEMO
• mruby for ET robot contest
sponsors
wanted!

4. Today's topic
• how to make mruby smaller
• why?
• how?

5. Why?

6. price RAM ROM mruby
LEGO
MindStorms
60,000yen 64MB 16MB OK
GR-PEACH 10,000yen 10MB 8MB OK
nucleo
F412ZG
3,000yen 256KB 1024KB OK
nucleo
F411RE
2,000yen 128KB 512KB OK
Arduino uno 3,000yen 2KB 32KB NG
porting microcomputers
ref)

7. F411RE or F401RE
F411RE F401RE
RAM:96KB
ROM:512KB
RAM:128KB
ROM:512KB

8. How?

9. how to reduce
A
B
C
reduce RAM
use ROM
tuning by #define
change
implementation

10. RAM size
0
40000
80000
120000
160000
default A B and C
66919
82783
152829

11. • DEMO

12. Assigned symbols to ROM

13. • why method definition in RAM?

14. RAM
Assigned symbols to ROM
predefined
method RAM
ROM
predefined
method
method
method

15. RAM
Assigned symbols to ROM
symbol
symbol
RAM
ROM
predefined
method
method
symbol
symbol
predefined
method
method

16. RAM
RAM
ROM
Assigned symbols to ROM
khash
method
khash
method
method

17. method table
struct RClass {
MRB_OBJECT_HEADER;
struct iv_tbl *iv;
struct kh_mt *mt;
struct RClass *super;
};
RClass

18. RAM
method table
keys
vals
typedef struct kh_mt{
khint_t n_buckets;
khint_t size;
khint_t n_occupied;
uint8_t *ed_flags;
mrb_sym *keys;
mrb_method_t *vals;
} kh_mt_t;
ed_flags
buckets
https://tatsu-zine.com/books/ruby-under-a-microscope-ja
"Ruby Under a Microscope"

19. method table
RClass
mt2
struct RClass {
MRB_OBJECT_HEADER;
struct iv_tbl *iv;
struct kh_mt *mt;
#ifdef USE_PRESYM
struct method_table *mt2;
#endif
struct RClass *super;
};

20. hash vs array
keys
vals
Array
RAM
ROM struct method_table{
mrb_sym sym;
mrb_method_t method;
};
typedef struct kh_mt{
khint_t n_buckets;
khint_t size;
khint_t n_occupied;
uint8_t *ed_flags;
mrb_sym *keys;
mrb_method_t *vals;
} kh_mt_t;
ed_flags
buckets
sym
method

21. Ruby method to C function
• Ex.String class
String class
to_i mrb_str_to_i
upcase mrb_str_upcase
length mrb_str_size
reverse mrb_str_reverse
size mrb_str_size
mrb_define_method(mrb, a, "size",mrb_str_size, MRB_ARGS_NONE());

22. Ruby method to C function
• perf
method name id
to_i 290
upcase 298
length 212
reverse 259
size 271
id function name
290 mrb_str_to_i
298 mrb_str_upcase
212 mrb_str_size
259 mrb_str_reverse
271 mrb_str_size

23. extract symbols
• *.c
• intern literal
• method
• const
• global const
• class
• module
• class method
• *.rb
• def
• class
mrb_intern_lit(mrb, "to_a")
mrb_define_class(mrb, "Array", mrb->object_class);
mrb_define_method(mrb, a, "+", mrb_ary_plus, MRB_ARGS_REQ(1));
mrb_define_method(mrb, a, "size",mrb_ary_size, MRB_ARGS_NONE());
class Foo
def foo
(...)
end
end

24. ROM
mrb_method_search_vm
Dynamically added methods
are defined here
method
RAM
khash
method

25. irep_remove_lv

26. remove local variable's names
• make bytecode without irep->lv
static void
irep_remove_lv(mrb_state *mrb, mrb_irep *irep)
{
int i;
if (irep->lv) {
mrb_free(mrb, irep->lv);
irep->lv = NULL;
}
for (i = 0; i < irep->rlen; ++i) {
irep_remove_lv(mrb, irep->reps[i]);
}
}

27. khash size
• KHASH_DEFAULT_SIZE 4
• KHASH_MIN_SIZE
#ifndef KHASH_DEFAULT_SIZE
# define KHASH_DEFAULT_SIZE 32
#endif
#define KHASH_MIN_SIZE 8
# define KHASH_DEFAULT_SIZE 4
#ifndef KHASH_DEFAULT_SIZE
# define KHASH_DEFAULT_SIZE 32
#endif
#define KHASH_MIN_SIZE 4

28. others

29. delete -g option
• mrbc.compile_options = "-g -B%{funcname} -o-"

30. • MRB_USE_ETEXT_EDATA
mrbconf.md
. = ALIGN(4);
_etext = .; /* define a global symbols at end of code
*/
} >FLASH
{
. = ALIGN(4);
_sdata = .; /* create a global symbol at data start */
*(.data) /* .data sections */
*(.data*) /* .data* sections */
. = ALIGN(4);
_edata = .; /* define a global symbol at data end */
} >RAM AT> FLASH

31. • MRB_HEAP_PAGE_SIZE
• Specifies number of `RBasic` per each heap
page.
• MRB_WORD_BOXING
• If defined represent `mrb_value` as a word.
• If defined `Float` will be a mruby object with
`RBasic`.
• MRB_STR_BUF_MIN_SIZE
• Specifies initial capacity of `RString` created
by `mrb_str_buf_new` function. mrbconf.md

32. Future works

33. RClass
mt2 to iv
RClass
struct RClass {
MRB_OBJECT_HEADER;
struct iv_tbl *iv;
struct kh_mt *mt;
#ifdef USE_PRESYM
struct method_table *mt2;
#endif
struct RClass *super;
};
iv
mt2
iv
mt2

34. • Implementation to unsupported class
• known bug
• "remove_method" can't remove method on
ROM
🙀

35. Thanks