This document summarizes the agenda for Metasepi team meeting #7. The meeting will include a demo of an RSS reader running on ARM hardware. It will discuss Ajhc, a Haskell compiler, and Metasepi, a Unix-like OS designed with strong typing. It aims to show how to use Ajhc to build an OS and "Snatch" an LED blinking application from a tiny OS to run as Haskell code using the forkOS API. The goal is to port the LED blinking thread from C to a Haskell program running on the OS.

1. Metasepi team meeting #7:
#7:
Snatch application on tiny OS
Kiwamu Okabe

2. Who am I?
☆ http://www.masterq.net/
☆ Twitter: @master_q
☆ Organizer of Metasepi project
☆ A developer of Ajhc Haskell compiler
☆ A Debian Maintainer
☆ 10 years' experience in developing
OS using NetBSD.

3. Agenda
☆ [1] Demo
☆ [2] What is Ajhc?
☆ [3] What is Metasepi?
☆ [4] What is compiler to build OS
☆ [5] How to use Ajhc
☆ [6] Snatch application on tiny OS
☆ [7] Let's Snatch it!

4. [1] Demo
☆ RSS reader running on mbed (ARM).
☆ Show reddit articles on LCD display.
☆ You can watch the movie following.
http://bit.ly/mbedmov

5. Demo hardware
Architecture: ARM Cortex-M3
RAM size: 64kB
IO: Ethernet, LED, LCD, SD Card, USB
host/device, Serial

6. Demo software
github.com/ajhc/demo-cortex-m3

7. [2] What is Ajhc?
http://ajhc.metasepi.org/
☆ Ajhc := A fork of jhc
☆ jhc := John's Haskell Compiler
☆ http://repetae.net/computer/jhc/
☆ Jhc outputs binary that has lowmemory-footprint and runs fast.
☆ Good for embedded software.

8. Why need Ajhc?
☆ GHC is de facto standard on Haskell.
☆ GHC := Glasgow Haskell Compiler
☆ http://www.haskell.org/ghc/
☆ Why need another Haskell compiler?
☆ To develop kernel named "Metasepi".

9. [3] What is Metasepi?
http://metasepi.org/
☆ Unix-like OS designed by strong type.
☆ Using ML or more strong type lang.
Haskell http://www.haskell.org/
OCaml http://caml.inria.fr/
MLton http://mlton.org/
. . . and suchlike.

10. Why need Metasepi?
☆ We have already Linux or Windows.
☆ But the developers are suffering.
☆ If use the kernel changed by you,
☆ you will get many runtime error.
☆ Difficult even to reproduce it.

11. Doesn't OSS have good quality?
☆ "The Cathedral and the Bazaar"
☆ "Given enough eyeballs, all bugs are
shallow."
http://cruel.org/freeware/cathedral.html
☆ But if you develop your own product
reusing OSS...

12. Low quality out of OSS umbrella

13. Type safety
☆ Less runtime errors.
☆ "数理科学的バグ撲滅方法論のすすめ"
http://itpro.nikkeibp.co.jp/article/COLUMN/20060915/248230/

14. Kernel desperately wants type
☆ Kernels are developed with C lang.
☆ Error on user space => SEGV
☆ Error on kernel space => halt!
☆ Should design kernel with the
greatest care.
☆ C language is safe?

15. [4] What is compiler to build OS
☆ Need strong type.
☆ Need flexibility such as C language.
☆ Create it if there are not!
☆ From scratch? No thank you...
☆ Look for our compiler base.

16. Want POSIX free compiler
Programs to print "hoge" on terminal.
The lesser depends on POSIX, the
smaller values.

17. Jhc output has only 20 undef
$ nm hs.out | grep
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
"U "
_IO_putc@@GLIBC_2.2.5
__libc_start_main@@GLIBC_2.2.5
_setjmp@@GLIBC_2.2.5
abort@@GLIBC_2.2.5
ctime@@GLIBC_2.2.5
exit@@GLIBC_2.2.5
fflush@@GLIBC_2.2.5
fprintf@@GLIBC_2.2.5
fputc@@GLIBC_2.2.5
fputs@@GLIBC_2.2.5
free@@GLIBC_2.2.5
fwrite@@GLIBC_2.2.5
getenv@@GLIBC_2.2.5
malloc@@GLIBC_2.2.5
memset@@GLIBC_2.2.5
posix_memalign@@GLIBC_2.2.5
realloc@@GLIBC_2.2.5
setlocale@@GLIBC_2.2.5
sysconf@@GLIBC_2.2.5
times@@GLIBC_2.2.5

18. Jhc is translator to C language

19. Easy to cross build

20. Survive burning out
Let's develop in dogfooding style. (The
method is called "Snatch".)

21. [5] How to use Ajhc
Case of Ubuntu 12.04 amd64.
$ sudo apt-get install haskell-platform libncurses5-dev gcc m4
$ cabal update
$ export PATH=$HOME/.cabal/bin/:$PATH
$ cabal install ajhc
$ which ajhc
/home/USER/.cabal/bin/ajhc
$ echo 'main = print "hoge"' > Hoge.hs
$ ajhc Hoge.hs
$ ./hs.out
"hoge"
You can use on Windows or Mac OS X.

22. Detail of usage
Please read "Ajhc User's Manual".
☆ ajhc.metasepi.org/manual.html
Also you can read in Japanese.
☆ ajhc.metasepi.org/manual_ja.html

23. [6] Snatch application on tiny OS
Snatch only the LED blinker thread.
☆ Board: STM32F4 Discovery
http://www.st.com/stm32f4-discovery
☆ OS: ChibiOS/RT
http://www.chibios.org/

24. Application code before Snatch
// File: main.c
#include "ch.h"
#include "hal.h"
#include "test.h"
static adcsample_t samples[ADC_GRP1_NUM_CHANNELS
ADC_GRP1_BUF_DEPTH];
static const ADCConversionGroup adcgrpcfg = {
// --snip-static PWMConfig pwmcfg = {
// --snip-static const SPIConfig spi2cfg = {
// --snip-static void pwmpcb(PWMDriver *pwmp) {
// --snip-void adccb(ADCDriver *adcp, adcsample_t *buffer,
// --snip-static void spicb(SPIDriver *spip) {
// --snip-static WORKING_AREA(waThread1, 128);
static msg_t Thread1(void *arg) {
// --snip-int main(void) {
// --snip--
*
size_t n) {

25. LED blinker thread
// File: main.c
static WORKING_AREA(waThread1, 128);
static msg_t Thread1(void *arg) {
(void)arg;
chRegSetThreadName("blinker");
while (TRUE) {
palSetPad(GPIOD, GPIOD_LED3);
chThdSleepMilliseconds(500);
palClearPad(GPIOD, GPIOD_LED3);
chThdSleepMilliseconds(500);
}
}
/* Orange. */
/* Orange. */
int main(void) {
// --snip-chThdCreateStatic(waThread1, sizeof(waThread1), NORMALPRIO,
Thread1, NULL);

26. Application design

27. [7] Let's Snatch it!
The source code at the following.
github.com/metasepi/chibios-arafura

28. Run simple Haskell code #1
-- File: hs_src/Main.hs
main :: IO ()
main = return ()
// File: main.c
static char malloc_heapstart[(2*1024)];
static MemoryHeap heap_desc;
void malloc_init(void) {
chHeapInit(&heap_desc, (void *)malloc_heapstart, (2*1024));
}
int main(void) {
// --snip-{ /* Init Ajhc RTS (Haskell) */
int hsargc = 1;
char *hsargv = "q";
char **hsargvp = &hsargv;
malloc_init();
hs_init(&hsargc, &hsargvp);
_amain();
}
chThdCreateStatic(waThread1, sizeof(waThread1), NORMALPRIO,
Thread1, NULL);

29. Run simple Haskell code #2

30. Blink LED only once #1
-- File: hs_src/Main.hs
foreign export ccall "blinkOrange" blinkOrange :: IO ()
blinkOrange :: IO ()
blinkOrange = do
c_palSetPad c_GPIOD c_GPIOD_LED3
c_chThdSleepMilliseconds 500
c_palClearPad c_GPIOD c_GPIOD_LED3
c_chThdSleepMilliseconds 500
// File: main.c
static WORKING_AREA(waThread1, 128);
static msg_t Thread1(void *arg) {
(void)arg;
chRegSetThreadName("blinker");
while (TRUE) {
blinkOrange(); // Haskell
}
}

31. Blink LED only once #2

32. Snatch blink thread code #1
-- File: hs_src/Main.hs
foreign export ccall "threadBlinkOrange" threadBlinkOrange :: IO ()
threadBlinkOrange :: IO ()
threadBlinkOrange = forever blinkOrange
// File: main.c
static WORKING_AREA(waThread1, 128);
static msg_t Thread1(void *arg) {
(void)arg;
threadBlinkOrange();
}

33. Snatch blink thread code #2

34. Use forkOS API #1
-- File: hs_src/Main.hs
main :: IO ()
main = void $ forkOS threadBlinkOrange
// File: conc_custom.c
void
forkOS_createThread_init()
{
chPoolInit(&pooldesc, THD_WA_SIZE(STACKSIZE), NULL);
chPoolLoadArray(&pooldesc, (void *) pool_buf, NTHREADS);
}
jhc_threadid_t
forkOS_createThread(void *(*wrapper) (void *),void *entry,int *err)
{
Thread *tid;
tid = chThdCreateFromMemoryPool(&pooldesc, NORMALPRIO,
(tfunc_t) wrapper, entry);
if (NULL == tid) { abort(); }
return tid;
}

35. Use forkOS API #2

36. GOAL !

37. PR: Call For Articles
☆ http://www.paraiso-lang.org/ikmsm/
☆ Fanzine of functional programming.
☆ About Haskell or OCaml or . . .
☆ Article about Ajhc in C84 book.
☆ Call me if you read it!
http://www.paraiso-lang.org/ikmsm/books/c85.html