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diff --git a/docs/tutorial/assembler.rst b/docs/tutorial/assembler.rst deleted file mode 100644 index 777600fc86..0000000000 --- a/docs/tutorial/assembler.rst +++ /dev/null @@ -1,123 +0,0 @@ -Inline assembler -================ - -Here you will learn how to write inline assembler in Micro Python. - -**Note**: this is an advanced tutorial, intended for those who already -know a bit about microcontrollers and assembly language. - -Micro Python includes an inline assembler. It allows you to write -assembly routines as a Python function, and you can call them as you would -a normal Python function. - -Returning a value ------------------ - -Inline assembler functions are denoted by a special function decorator. -Let's start with the simplest example:: - - @micropython.asm_thumb - def fun(): - movw(r0, 42) - -You can enter this in a script or at the REPL. This function takes no -arguments and returns the number 42. ``r0`` is a register, and the value -in this register when the function returns is the value that is returned. -Micro Python always interprets the ``r0`` as an integer, and converts it to an -integer object for the caller. - -If you run ``print(fun())`` you will see it print out 42. - -Accessing peripherals ---------------------- - -For something a bit more complicated, let's turn on an LED:: - - @micropython.asm_thumb - def led_on(): - movwt(r0, stm.GPIOA) - movw(r1, 1 << 13) - strh(r1, [r0, stm.GPIO_BSRRL]) - -This code uses a few new concepts: - - - ``stm`` is a module which provides a set of constants for easy - access to the registers of the pyboard's microcontroller. Try - running ``import stm`` and then ``help(stm)`` at the REPL. It will - give you a list of all the available constants. - - - ``stm.GPIOA`` is the address in memory of the GPIOA peripheral. - On the pyboard, the red LED is on port A, pin PA13. - - - ``movwt`` moves a 32-bit number into a register. It is a convenience - function that turns into 2 thumb instructions: ``movw`` followed by ``movt``. - The ``movt`` also shifts the immediate value right by 16 bits. - - - ``strh`` stores a half-word (16 bits). The instruction above stores - the lower 16-bits of ``r1`` into the memory location ``r0 + stm.GPIO_BSRRL``. - This has the effect of setting high all those pins on port A for which - the corresponding bit in ``r0`` is set. In our example above, the 13th - bit in ``r0`` is set, so PA13 is pulled high. This turns on the red LED. - -Accepting arguments -------------------- - -Inline assembler functions can accept up to 3 arguments. If they are -used, they must be named ``r0``, ``r1`` and ``r2`` to reflect the registers -and the calling conventions. - -Here is a function that adds its arguments:: - - @micropython.asm_thumb - def asm_add(r0, r1): - add(r0, r0, r1) - -This performs the computation ``r0 = r0 + r1``. Since the result is put -in ``r0``, that is what is returned. Try ``asm_add(1, 2)``, it should return -3. - -Loops ------ - -We can assign labels with ``label(my_label)``, and branch to them using -``b(my_label)``, or a conditional branch like ``bgt(my_label)``. - -The following example flashes the green LED. It flashes it ``r0`` times. :: - - @micropython.asm_thumb - def flash_led(r0): - # get the GPIOA address in r1 - movwt(r1, stm.GPIOA) - - # get the bit mask for PA14 (the pin LED #2 is on) - movw(r2, 1 << 14) - - b(loop_entry) - - label(loop1) - - # turn LED on - strh(r2, [r1, stm.GPIO_BSRRL]) - - # delay for a bit - movwt(r4, 5599900) - label(delay_on) - sub(r4, r4, 1) - cmp(r4, 0) - bgt(delay_on) - - # turn LED off - strh(r2, [r1, stm.GPIO_BSRRH]) - - # delay for a bit - movwt(r4, 5599900) - label(delay_off) - sub(r4, r4, 1) - cmp(r4, 0) - bgt(delay_off) - - # loop r0 times - sub(r0, r0, 1) - label(loop_entry) - cmp(r0, 0) - bgt(loop1) |