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------------------------------------------------------------------------------
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-- --
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-- Copyright (C) 2019-2020, AdaCore --
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-- --
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-- Redistribution and use in source and binary forms, with or without --
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-- modification, are permitted provided that the following conditions are --
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-- met: --
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-- 1. Redistributions of source code must retain the above copyright --
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-- notice, this list of conditions and the following disclaimer. --
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-- 2. Redistributions in binary form must reproduce the above copyright --
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-- notice, this list of conditions and the following disclaimer in --
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-- the documentation and/or other materials provided with the --
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-- distribution. --
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-- 3. Neither the name of the copyright holder nor the names of its --
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-- contributors may be used to endorse or promote products derived --
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-- from this software without specific prior written permission. --
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-- --
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-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS --
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-- "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT --
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-- LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR --
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-- A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT --
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-- HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, --
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-- SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT --
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-- LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, --
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-- DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY --
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-- THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT --
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-- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE --
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-- OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. --
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-- --
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------------------------------------------------------------------------------
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-- Bit-bang a sequence of color LED values to a one-pin LED strip (WS2812B
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-- or similar).
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with System.Machine_Code; use System, System.Machine_Code;
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with NRF_SVD.GPIO; use NRF_SVD.GPIO;
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with MicroBit.Time;
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package body MicroBit.IOs.NeoPixel is
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-----------
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-- Write --
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-----------
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procedure Write (Pin : Pin_Id; Values : UInt8_Array) is
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Point : constant GPIO_Point := Points (Pin);
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Mask : constant UInt32 := 2 ** Point.Pin;
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EOL : constant String := ASCII.LF & ASCII.HT;
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begin
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-- Set pin to digital out mode and reset strip
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Set (Pin, False);
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MicroBit.Time.Delay_Ms (1);
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-- The following loop is very time-sensitive. The bit frame is 1.25 <EFBFBD>s,
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-- i.e. 20 cycles of the 16 MHz clock. So, we run it with IRQs disabled,
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-- and carefully account for every cycle.
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-- Code taken from:
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-- https://github.com/Microsoft/pxt-ws2812b/blob/master/sendBuffer.asm
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Asm (" cpsid i @ disable irq" & EOL &
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" b .start" & EOL &
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".nextbit: @ c0" & EOL &
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" str %2, [%1, #0] @ pin := hi c2" & EOL &
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" tst r6, r0 @ c3" & EOL &
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" bne .islate @ c4" & EOL &
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" str %2, [%0, #0] @ pin := lo c6" & EOL &
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".islate:" & EOL &
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" lsr r6, r6, #1 @ r6 >>= 1 c7" & EOL &
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" bne .justbit @ c8" & EOL &
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"@ not just a bit - need new byte" & EOL &
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" add %3, #1 @ buf++ c9" & EOL &
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" sub %4, #1 @ len-- c10" & EOL &
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" bcc .stop @ if (len<0) goto .stop c11" & EOL &
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".start:" & EOL &
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" movs r6, #0x80 @ reset mask c12" & EOL &
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" nop @ c13" & EOL &
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".common: @ c13" & EOL &
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" str %2, [%0, #0] @ pin := lo c15" & EOL &
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" @ always re-load byte - it just fits with the" & EOL &
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" @ cycles better this way." & EOL &
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" ldrb r0, [%3, #0] @ r0 := *buf c17" & EOL &
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" b .nextbit @ c20" & EOL &
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".justbit: @ c10" & EOL &
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" @ no nops, branch taken is already 3 cycles" & EOL &
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" b .common @ c13" & EOL &
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".stop:" & EOL &
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" str %2, [%0, #0] @ pin := lo" & EOL &
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" cpsie i @ enable irq",
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Inputs => (Address'Asm_Input ("l", GPIO_Periph_0.OUTCLR'Address), -- %0
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Address'Asm_Input ("l", GPIO_Periph_0.OUTSET'Address), -- %1
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UInt32'Asm_Input ("l", Mask), -- %2
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Address'Asm_Input ("l", Values'Address), -- %3
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Natural'Asm_Input ("l", Values'Length)), -- %4
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Volatile => True,
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Clobber => "r0,r6");
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end Write;
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end MicroBit.IOs.NeoPixel;
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