@
@    Mecrisp-Stellaris - A native code Forth implementation for ARM-Cortex M microcontrollers
@    Copyright (C) 2013  Matthias Koch
@
@    This program is free software: you can redistribute it and/or modify
@    it under the terms of the GNU General Public License as published by
@    the Free Software Foundation, either version 3 of the License, or
@    (at your option) any later version.
@
@    This program is distributed in the hope that it will be useful,
@    but WITHOUT ANY WARRANTY; without even the implied warranty of
@    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
@    GNU General Public License for more details.
@
@    You should have received a copy of the GNU General Public License
@    along with this program.  If not, see <http://www.gnu.org/licenses/>.
@

;------------------------------------------------------------------------------
This is the seventh experimental release of Mecrisp-Stellaris,
a port of Mecrisp to the ARM Cortex M architecture.

It runs out of the box on:
  - TI Stellaris Launchpad       with LM4F120H5QR
  - STM F4 Discovery             with STM32F407VGT6 
  - Freescale Freedom FRDM-KL25Z with KL25Z128VLK4

http://mecrisp.sourceforge.net/

m-atthias@users.sf.net
;------------------------------------------------------------------------------

Mecrisp finally got a younger sister and mastered the jump
to the ARM Cortex M Thumb-2 instruction set.

They share most of the design ideas, so Mecrisp-Stellaris can compile 
directly into Flash, generates native code with constant folding and
inlining of short words. 

Communication is via serial 115200 baud 8N1 over
  - UART0  in LM4F120  (connected to USB-serial bridge on Stellaris Launchpad)
  - USART2 in STM32F4  (TX on PA2, RX on PA3)
  - UART0  in KL25Z128 (connected to USB-serial bridge on Freedom board)

Hardware and configuration for LM4F120:
  Connect your cable to the Debug-USB-Port, 
  set "PWR SELECT" switch to DEBUG and
  close VDD jumper.

  Flashing is possible with lm4flash:
  https://github.com/utzig/lm4tools

  On startup, this runs with internal PIOSC at 16 MHz, 
  which is specified +-3% over whole temperature range.

Hardware and configuration for STM32F4:
  Connect USB cable to ST-Link USB port,
  connect your favourite serial link to PA2 (TX) and PA3 (RX),
  keep logic voltage levels in mind !
  
  Flashing is possible with st-flash:
  https://github.com/texane/stlink

  Flash memory is mirrored in hardware starting from address 0. Mecrisp uses
  the low address range to generate short opcodes for calling core words, but
  for flashing the binary, you have to use the "true address" $08000000.
  st-flash write mecrisp-stellaris-stm32f4.bin 0x08000000

  On startup, this runs with external 8 MHz crystal HSE clock,
  as internal oscillator is specified -8% + 4.5% over whole temp range.

Hardware and configuration for KL25Z128:
  Connect USB cable to SDA-USB-PORT

  Flashing is via mass storage interface -
    the board will appear as Flash Disk, just copy .srec file in.
    Maybe you have to do an OpenSDA firmware update before.

  On startup, this runs with internal FLL at 20.97 MHz. 


Mecrisp-Stellaris itself is sending LF for line ending,
but recognizes both LF and CR. Invoke Picocom with something like
picocom -b 115200 /dev/ttyACM0 --imap lfcrlf,crcrlf --omap delbs,crlf

For changing line ending to CR-LF or whatever else you like,
look at the beginning of mecrisp-stellaris-....s.

Assembling is done with the GCC-Arm-Embedded toolchain:
https://launchpad.net/gcc-arm-embedded/


Differences to stable Mecrisp for MSP430 are:

* Experimental code ! Be brave, but expect monsters around the corner.

* Fetch-Modify-Store operations like +! or bic! are not atomic.

* Comfortable hardware support is done in Forth this time.
   You can contribute your favourite hardware handling routines 
   to be included in upcoming releases !

* Mecrisp-Stellaris for now has no double-number support, if you wish for it,
   feel free to ask me to implement it !

* For design ideas, have a look into Mecrisp for MSP430, too !

* Chip specific source has added English comments and hints included
    for simplify porting to other ARM Cortex-M chips.

;------------------------------------------------------------------------------
; Porting
;------------------------------------------------------------------------------

Mecrisp-Stellaris can assemble without change for M0, M3 and M4 cores.

M0 cores lack conditional execution "ite eq...", which has to be circumvented 
by conditional branches. stmdb psp!, {tos} is missing, which I use to push to 
data stack and they have no division in hardware. 

There is an assembler switch "m0core" to assemble the core with replacement 
code for ARM Cortex-M0 chips. Depending on your flash capabilities, there are
two useful switches: 

  "charkommaavailable" which is self-explaining and 
  "emulated16bitflashwrites" if your particular Flash controller
                             cannot write data in separate 16-Bit chunks.

Core needs about 11 kb flash at the moment, but reserves 16 kb for upcoming
additions, and needs 1.5 kb RAM for stacks and buffers plus variables for 
interrupt handlers plus RAM dictionary space. Bare minimum for ARM to get it 
running will be around 16kb/2kb, but to have fun with it and leave space for 
real applications, go with at least of 32 kb flash and 4 kb RAM. 

Look at the flash specification for your particular chip.

The compiler only depends on 2-aligned 16-Bit flash writes
one time per location, you can remove c, and align, without issues 
from the compiler, but 8-Bit flash writes are nice to have 
for compatibility with standard code. 

For special cases having only 4-aligned 32-bit one-time writes to Flash,
there is a hflash! emulation layer.

Flash erasing is only available for the user, it doesn't need erase cycles 
while compiling. 

Keep these criteria in mind, pick your favourite chip and add it as your 
contribution. It won't be too difficult, start with an UART echo written 
in assembly without libraries, and I will be there for your help.

You have to change memory map, hardware initialisation and interrupt vectors,
write ?key, key, emit for a first reaction and flash write access
for final success. There is a common mimimum set of handlers across 
ARM Cortex CPUs, which will help you to get it running for the first time.

Unfortunately, there is a lot of bit twiddling necessary for peripherial 
modules, as they differ a lot across manufacturers. ARMs seem to only share 
core components like CPU, interrupt controler and a very basic systick timer.

I don't have the time to support a lot of different chips with examples. 

TI ADCs have a sequencer FIFO buffer, ST ADCs need a DMA channel configured. 
TI Flash controller offers 32 bit aligned writes only, but as many as you 
wish per location until all bits are zero; 
ST-M3 have 16 bit aligned Flash write only, 
ST-M4 have 8 bit, 16 bit and 32 bit Flash writes available, 
but only once per location. 

I would like to focus on core development, support porting to other chips and 
families with adaptions in core, but leave writing initialisation code, 
testing and writing Forth examples to "family maintainers" which are deep 
into their chip of choice. 


;------------------------------------------------------------------------------
Here comes a word list,
  with short descriptions of all currently included words:
View it with fixed-width font !
;------------------------------------------------------------------------------

;------------------------------------------------------------------------------
; Terminal-IO
;------------------------------------------------------------------------------

        ?key            ( -- Flag ) Checks if a key is waiting
        key             ( -- Char ) Waits for and fetches the pressed key
        emit            ( Char -- ) Emits a character.

;------------------------------------------------------------------------------
; Stack Jugglers  (exactly ANS, some logical extensions)
;------------------------------------------------------------------------------

Single-Jugglers:

        depth           ( -- +n ) Gives number of single-cell stack items.
        nip             ( x1 x2 -- x2 )
        drop            ( x -- )
        rot             ( x1 x2 x3 -- x2 x3 x1 )
        -rot            ( x1 x2 x3 -- x3 x1 x2 )
        swap            ( x1 x2 -- x2 x1 )
        tuck            ( x1 x2 -- x2 x1 x2 )
        over            ( x1 x2 -- x1 x2 x1 )
        ?dup            ( x -- 0 | x x )
        dup             ( x -- x x )
        pick            ( ... xi+1 xi ... x1 x0 i -- ... x1 x0 xi )
                                  Picks one element from deep below

        >r              ( x -- ) (R: -- x )
        r>              ( -- x ) (R: x -- )
        r@              ( -- x ) (R: x -- x )

;------------------------------------------------------------------------------
; Logic  (exactly ANS, some logical extensions)
;------------------------------------------------------------------------------

        arshift         ( x1 u -- x2 ) Arithmetric right-shift of u bit-places
        rshift          ( x1 u -- x2 ) Logical right-shift of u bit-places
        lshift          ( x1 u -- x2 ) Logical  left-shift of u bit-places
        shr             ( x1 -- x2 )   Logical right-shift of one bit-place
        shl             ( x1 -- x2 )   Logical  left-shift of one bit-place
        bic             ( x1 x2 -- x3 ) Bit clear, identical to "not and"
        not             ( x1 -- x2 )   Invert all bits
        xor             ( x1 x2 -- x3 ) Bitwise Exclusive-OR
        or              ( x1 x2 -- x3 ) Bitwise OR
        and             ( x1 x2 -- x3 ) Bitwise AND
        clz             ( x1 -- u ) Count leading zeros
        false           ( --  0 ) False-Flag
        true            ( -- -1 ) True-Flag

;------------------------------------------------------------------------------
; Calculus for single numbers  (exactly ANS, some logical extensions)
;------------------------------------------------------------------------------
        u/mod           ( u1 u2 -- u3 u4 ) 32/32 = 32 rem 32 Division
                                           u1 / u2 = u4 remainder u3
        /mod            ( n1 n2 -- n3 n4 ) n1 / n2 = n4 rem n3
        /               ( n1 n2 -- n3 ) n1 / n2 = n3
        *               ( u1|n1 u2|n2 -- u3|n3 ) 32*32 = 32 Multiplication
        min             ( n1 n2 -- n1|n2 ) Keeps smaller of top two items
        max             ( n1 n2 -- n1|n2 ) Keeps greater of top two items
        umin            ( u1 u2 -- u1|u2 ) Keeps unsigned smaller
        umax            ( u1 u2 -- u1|u2 ) Keeps unsigned greater
        2-              ( u1|n1 -- u2|n2 ) Subtracts two, optimized
        1-              ( u1|n1 -- u2|n2 ) Subtracts one, optimized
        2+              ( u1|n1 -- u2|n2 ) Adds two, optimized
        1+              ( u1|n1 -- u2|n2 ) Adds one, optimized
        even            ( u1|n1 -- u2|n2 ) Makes even. Adds one if uneven.
        2*              ( n1 -- n2 ) Arithmetric  left-shift
        2/              ( n1 -- n2 ) Arithmetric right-shift
        abs             ( n -- u ) Absolute value
        negate          ( n1 -- n2 ) Negate
        -               ( u1|n1 u2|n2 -- u3|n3 ) Subtraction
        +               ( u1|n1 u2|n2 -- u3|n3 ) Addition

;------------------------------------------------------------------------------
; Comparisions  (exactly ANS, some logical extensions)
;------------------------------------------------------------------------------

        u<=             ( u1 u2 -- flag )  Unsigned comparisions
        u>=             ( u1 u2 -- flag )
        u>              ( u1 u2 -- flag )
        u<              ( u1 u2 -- flag )
        <=              ( n1 n2 -- flag )    Signed comparisions
        >=              ( n1 n2 -- flag )
        >               ( n1 n2 -- flag )
        <               ( n1 n2 -- flag )
        0<              ( n - flag )         Negative ?
        0<>             ( x -- flag )
        0=              ( x -- flag )
        <>              ( x1 x2 -- flag )
        =               ( x1 x2 -- flag )

;------------------------------------------------------------------------------
; Number base  (exactly ANS)
;------------------------------------------------------------------------------

        binary          ( -- ) Sets base to 2
        decimal         ( -- ) Sets base to 10
        hex             ( -- ) Sets base to 16
        base            ( -- a-addr ) Base variable address

;------------------------------------------------------------------------------
; Memory access  (subtle differences to ANS, special cpu-specific extensions)
;------------------------------------------------------------------------------

        move            ( c-addr1 c-addr2 u -- ) Moves u Bytes in Memory
                        Caution with overlapping areas, as for now it moves
                        in forward direction only.

        cbit@           ( mask c-addr -- flag ) Test BIts in byte-location
        hbit@           ( mask a-addr -- flag ) Test BIts in halfword-location
        bit@            ( mask a-addr -- flag ) Test BIts in word-location

        cxor!           ( mask c-addr -- ) Toggle bits in byte-location
        hxor!           ( mask a-addr -- ) Toggle bits in halfword-location
        xor!            ( mask a-addr -- ) Toggle bits in word-location

        cbic!           ( mask c-addr -- ) Clear BIts in byte-location
        hbic!           ( mask a-addr -- ) Clear BIts in halfword-location
        bic!            ( mask a-addr -- ) Clear BIts in word-location

        cbis!           ( mask c-addr -- ) Set BIts in byte-location
        hbis!           ( mask a-addr -- ) Set BIts in halfword-location
        bis!            ( mask a-addr -- ) Set BIts in word-location

        constant  name  ( u|n -- )  Makes a single constant.
        variable  name  ( n|n -- )  Makes an initialized single variable


        @               ( a-addr -- u|n ) Fetches single number from memory
        !               ( u|n a-addr -- ) Stores single number in memory
        +!              ( u|n a-addr -- ) Add to memory location

        h@              ( c-addr -- char ) Fetches halfword from memory
        h+!             ( u|n a-addr -- ) Add to halfword memory location
        h!              ( char c-addr ) Stores halfword in memory

        c@              ( c-addr -- char ) Fetches byte from memory
        c!              ( char c-addr ) Stores byte in memory
        c+!             ( u|n a-addr -- ) Add to byte memory location

;------------------------------------------------------------------------------
; Strings and beautiful output (subtle differences to ANS)
;------------------------------------------------------------------------------

String routines:
        compare         ( cstr-addr-1 cstr-addr-2 -- flag )
                        Compares two counted strings

        type            ( cstr-addr -- )
                        Prints a counted string.

        s" Hello"       Compiles a string and
                        ( -- cstr-addr )
                        gives back its address when executed.

        ." Hello"       Compiles a string and
                        ( -- )
                        prints it when executed.

        bl              ( -- 32 ) ASCII code for Space
        space           ( -- ) Emits space
        cr              ( -- ) Emits line feed

Pictured numerical output:
        .digit          ( u -- char ) Converts a digit to a char
        digit           ( char -- u ) Converts a char to a digit

        number          ( Counted-String-Address -- 0 )
                          cstr-addr              -- n 1 )
                        Tries to convert a string to a number.

        [char] *        Compiles code of following char
                        ( -- char ) when executed

        char *          ( -- char ) gives code of following char
        hold            ( char -- ) Adds character to pictured number
                                    output buffer from the front.

        sign            ( n -- ) Add a minus sign to pictured number
                                 output buffer, if n is negative

        #S              ( u1|n1 -- 0 0 ) Add all remaining digits
                        from the single length number to output buffer
        #               ( u1|n1 -- u2|n2 ) Add one digit from the
                        single length number to output buffer
        #>              ( u|n -- cstr-addr )
                        Drops number and finishes
                        pictured numeric output ready for type
        <#              ( -- ) Prepare pictured number output buffer
        u.              ( u -- ) Print unsigned single number
        .               ( n -- ) Print single number

Deep insights:
        words           ( -- ) Prints list of defined words.
        .s              ( many -- many ) Prints stack contents
        dump            ( addr -- ) Dumps a bit of memory
        hex.            ( u -- ) Prints 32 bit unsigned in hex base,
                                 needs emit only.
                                 This is independent of number subsystem.

;------------------------------------------------------------------------------
; User input and its interpretation (more FIG style, speciality!)
;------------------------------------------------------------------------------

        query           ( -- ) Fetches user input to input buffer
        token           ( -- cstr-addr ) Cuts one token out of input buffer
        parse           ( char -- cstr-addr )
                        Cuts anything delimited by char out of input buffer

        interpret       ( any -- any ) Execute, compile, fold, optimize...
        quit            ( many -- ) (R: many -- ) Resets Stacks

;------------------------------------------------------------------------------
; Dictionary expansion  (speciality!)
;------------------------------------------------------------------------------

        ,               ( u|n -- ) Appends a single number to dictionary
        ><,             ( u|n -- ) Reverses high and low-halfword, then 
                                     appends it to dictionary
        h,              ( u|n -- ) Appends a halfword to dictionary
        string,         ( cstr-addr -- ) Inserts a string without runtime
        literal,        ( u|n -- ) Compiles a literal with runtime
        inline,         ( a-addr -- ) Inlines the choosen subroutine
        call,           ( a-addr -- ) Compiles a call to a subroutine
        jump,           ( Hole-for-Opcode Destination ) 
                        Writes an unconditional Jump
                        to a-addr-Destination with the given Bitmask as
                        Opcode into the halfword sized a-addr-Hole
        cjump,          ( Hole-for-Opcode Destination Bitmask ) 
                        Writes a conditional Jump
                        to a-addr-Destination with the given Bitmask as
                        Opcode into the halfword sized a-addr-Hole
        ret,            ( -- ) Compiles a ret opcode
        allot           ( n -- ) Tries to advance Dictionary Pointer by n bytes
                                 Aborts, if not enough space available
        here            ( -- a-addr|c-addr )
                        Gives current position in Dictionary
        dictionarystart ( -- a-addr ) Current entry point for dictionary search

        compiletoram    ( -- ) Makes ram   the target for compiling
        compiletoflash  ( -- ) Makes flash the target for compiling

  
    Available depending on chip capabilities:

        c,              ( char -- ) Appends a byte to dictionary
        align,          ( -- ) Makes Dictionary Pointer even, if uneven.
        align4,         ( -- ) Aligns on 4. M0 only

        movwmovt,       ( x Register -- ) Generate a movw/movt-Sequence to
                                          get x into given Register. M3/M4 only
       registerliteral, ( x Register -- ) Generate a movs-lsls-adds... sequence 
                                          to get x into given Register. M0 only

;------------------------------------------------------------------------------
; Flags and inventory  (speciality!)
;------------------------------------------------------------------------------

        smudge          ( -- ) Makes current definition visible, burns
                               collected flags to flash and
                               takes care of proper ending
        inline          ( -- ) Makes current definition inlineable.
                               For flash, place it inside your definition !
        immediate       ( -- ) Makes current definition immediate.
                               For flash, place it inside your definition !
        setflags        ( char -- ) Sets Flags with a mask. This isn't immediate,
                               but for flash, place it inside your definition !
        create name     ( -- ) Creates and links a new invisible dictionary
                               header that does nothing.
                               Use FIG-style <builds .. does> !
        find            ( cstr-addr -- a-addr flags )
                               Searches for a String in Dictionary.
                               Gives back flags, which are different to ANS !

        0-foldable      ( -- ) Current word becomes foldable with zero constants
        1-foldable      ( -- ) Current word becomes foldable with one constants
        2-foldable      ( -- ) Current word becomes foldable with two constants
        3-foldable      ( -- ) Current word becomes foldable with 3   constants

;------------------------------------------------------------------------------
; Compiler essentials  (subtle differences to ANS)
;------------------------------------------------------------------------------

        execute         ( a-addr -- ) Calls subroutine
        recurse         ( -- ) Lets the current definition call itself
        ' name          ( -- a-addr ) Tries to find name in dictionary
                                      gives back executable address
        ['] name        ( -- a-addr)  Tick that compiles the executable address
                                      of found word as literal
        postpone name   ( -- ) Helps compiling immediate words.
        does>           ( -- ) executes: ( -- a-addr )
                               Gives address to where you have stored data.
        <builds         ( -- ) Makes Dictionary header and reserves space
                               for special call.
        state           ( -- a-addr ) Address of state variable
        ]               ( -- ) Switch to compile state
        [               ( -- ) Switch to execute state
        ;               ( -- ) Finishes new definition
        : name          ( -- ) Opens new definition

;------------------------------------------------------------------------------
; Control structures (exactly ANS)
;------------------------------------------------------------------------------
Internally, they have complicated compile-time stack effects.

Decisions:

flag if ... then
flag if ... else ... then

        then            ( -- )           This is the common
        else            ( -- )           flag if ... [else ...] then
        if              ( flag -- )      structure.

Case:

n case
     m1   of ... endof
     m2   .. ... .....
   flag  ?of ... endof
    all others
  endcase

        case            ( n -- n )       Begins case structure
        of              ( m -- )         Compares m with n, choose this if n=m
        ?of             ( flag -- )      Flag-of, for custom comparisions
        endof           ( -- )           End of one possibility
        endcase         ( n -- )         Ends case structure, discards n

Indefinite Loops:

begin ... again
begin ... flag until
begin ... flag while ... repeat

        repeat          ( -- ) Finish of a middle-flag-checking loop.

        while           ( flag -- ) Check a flag in the middle of a loop

        until           ( flag -- ) begin ... flag until
                                    loops as long flag is true
        again           ( -- )  begin ... again
                                is an endless loop
        begin           ( -- )


Definite Loops:

limit index   do ... [one or more leave(s)] ... loop
             ?do ... [one or more leave(s)] ... loop
              do ... [one or more leave(s)] ... n +loop
             ?do ... [one or more leave(s)] ... n +loop


        k               ( -- u|n ) Gives third  loop index
        j               ( -- u|n ) Gives second loop index
        i               ( -- u|n ) Gives innermost loop index


        unloop          (R: old-limit old-index -- )
                        Drops innermost loop structure,
                        pops back old loop structures to loop registers

        exit            ( -- ) Returns from current definition.
                               Compiles a ret opcode.

        leave           ( -- ) (R: old-limit old-index -- )
                        Leaves current innermost loop promptly

        +loop           ( u|n -- )
                        (R: unchanged | old-limit old-index -- )
                        Adds number to current loop index register
                        and checks whether to continue or not

        loop            ( -- )
                        (R: unchanged | old-limit old-index -- )
                        Increments current loop index register by one
                        and checks whether to continue or not.

        ?do             ( Limit Index -- )
                        (R: unchanged | -- old-limit old-index )
                        Begins a loop if limit and index are not equal

        do              ( Limit Index -- )
                        (R: -- old-limit old-index )
                        Begins a loop

;------------------------------------------------------------------------------
; Common Hardware access
;------------------------------------------------------------------------------
        dint            ( -- ) Disables Interrupts
        eint            ( -- ) Enables  Interrupts
        nop             ( -- ) No Operation. Hook for unused IRQs !

        irq-systick     ( -- a-addr ) Memory locations for IRQ-Hooks

;------------------------------------------------------------------------------
; Specials for LM4F120:
;------------------------------------------------------------------------------

Flash:
        eraseflash      ( -- ) Erases everything. Clears Ram. Restarts Forth.

        eraseflashfrom  ( a-addr -- ) Starts erasing at this address.
                                      Clears Ram. Restarts Forth.

        flashpageerase  ( a-addr -- ) Erase one 1k flash page only. Take care:
                                      No Reset, no dictionary reinitialisation.

        cflash!         ( char c-addr -- )  Writes byte to flash
        hflash!         ( u|n a-addr -- )   Writes halfword to flash
        flash!          ( u|n 4-a-addr -- ) Writes single number to flash, 
                                              4 aligned !
Interrupts:

        irq-porta       ( -- a-addr ) Memory locations for IRQ-Hooks
        irq-portb
        irq-portc
        irq-portd
        irq-porte
        irq-portf
        irq-timer0a
        irq-timer0b
        irq-timer1a
        irq-timer1b
        irq-timer2a
        irq-timer2b
        irq-adc0seq0
        irq-adc0seq1
        irq-adc0seq2
        irq-adc0seq3

  Look into vectors.s and interrupts.s to add more interrupts.
  
;------------------------------------------------------------------------------
; Specials for STM32F4:
;------------------------------------------------------------------------------

Flash:
        eraseflash       ( -- ) Erases everything. Clears Ram. Restarts Forth.
        eraseflashsector ( u -- ) Erases one sector of Flash

        cflash!         ( char c-addr -- )  Writes byte to flash
        hflash!         ( u|n a-addr -- )   Writes halfword to flash

Interrupts:

        irq-adc         ( -- a-addr ) Memory locations for IRQ-Hooks
        irq-exti4
        irq-exti3
        irq-exti2
        irq-exti1
        irq-exti0

  Look into vectors.s and interrupts.s to add more interrupts.

;------------------------------------------------------------------------------
; Specials for KL25Z128:
;------------------------------------------------------------------------------

Flash:
        eraseflash      ( -- ) Erases everything. Clears Ram. Restarts Forth.

        eraseflashfrom  ( a-addr -- ) Starts erasing at this address.
                                      Clears Ram. Restarts Forth.

        flashpageerase  ( a-addr -- ) Erase one 1k flash page only. Take care:
                                      No Reset, no dictionary reinitialisation.

        hflash!         ( u|n a-addr -- )   Writes halfword to flash - emulated
        flash!          ( u|n 4-a-addr -- ) Writes single number to flash, 
                                              4 aligned !

Interrupts are coming soon...

Matthias Koch, Summer 2013
