NeoPixel Data Transfer Internals

Macros
#define	NPDATA_FRAME_IDX_DEFAULT   (0U)
	Default value for npdata_frame_idx.
#define	NPDATA_COLOR_BIT_DEFAULT   (NPDATA_SHIFT_REG_MASK)
	Default value for npdata_color_bit.
#define	NPDATA_SHIFT_REG_MASK   (UINT32_C(1) << (NEOPIXEL_COLOR_BITS - 1))
	Mask for selecting the current data bit when converting color bytes to timing data.

Functions
static void	push_data_to_buffer (uint32_t *const p_block)
	Push new data to the secondary (or primary) buffer. More...
static volatile uint32_t npdata_gpt_buffer[2][(8U)]	__attribute__ ((aligned(4)))
	GPT compare ping-pong buffer for generating NeoPixel timing waveforms.
volatile color_rgb_t *	npdata_frame_buffer_get (void)
	Gets a pointer to the frame buffer. More...
void	npdata_frame_send (void)
	Kicks off a frame transmission to the attached NeoPixels.
void	npdata_open (void)
	Opens the peripherals needed for data transmission to the NeoPixels.
void	npdata_color_set (uint32_t index, color_rgb_t const *const p_color)
	Copies a color to the specified index of the frame buffer. More...
transfer_status_t	npdata_status_get (void)
	Gets the current status of the NeoPixel data transfer. More...

Variables
volatile color_rgb_t	g_npdata_frame [(4U)] = {0}
	NeoPixel frame buffer.
static uint32_t	npdata_frame_cnt = 0
static uint32_t	npdata_frame_idx = (0U)
	Current NeoPixel index to write to the buffers.
static uint32_t	npdata_color_bit = ( (UINT32_C(1) << (NEOPIXEL_COLOR_BITS - 1)) )
	Current bit to write to the buffers.
static uint32_t	npdata_color_word = 0U
	Current full shift-register word for the color being written.
static uint32_t	npdata_b0_counts = 0
	Timer counts for the high period of a 0-bit.
static uint32_t	npdata_b1_counts = 0
	Timer counts for the high period of a 1-bit.

ISR functions and callbacks
void	dmac0_repeat_isr (void)
	DMAC_INT ISR handler. More...
void	npdata_transfer_callback (dmac_callback_args_t *p_args)
	DMAC interrupt callback; unused. More...

Detailed Description

Operation

A pulse-code waveform is transmitted at 800 kHz. To achieve this, the Capture Compare B channel is utilized. The DMAC is configured to ping-pong between two buffers and set the timing data to the capture compare of the GPT. Using ping-pong buffering allows an overall smaller buffer footprint since the timing data can be calculated on the fly for each NeoPixel. Otherwise a buffer would be needed that is 24 uint32 words for each NeoPixel.

Function Documentation

dmac0_repeat_isr()

void dmac0_repeat_isr

(

void

)

DMAC_INT ISR handler.

Note

This overrides the built-in FSP DMAC ISR.

This is setup to trigger on each repeat size completion.

npdata_color_set()

void npdata_color_set	(	uint32_t	index,
		color_rgb_t const *const	p_color
	)

Copies a color to the specified index of the frame buffer.

Parameters

	index	The index to write.
[in]	p_color	Pointer to the color to copy.

npdata_frame_buffer_get()

volatile color_rgb_t * npdata_frame_buffer_get

(

void

)

Gets a pointer to the frame buffer.

Warning

Do not write to the frame buffer while npdata_status_get() returns TRANSFER_STATUS_WORKING.

npdata_status_get()

transfer_status_t npdata_status_get

(

void

)

Gets the current status of the NeoPixel data transfer.

Return values

TRANSFER_STATUS_IDLE	No transfers are active.
TRANSFER_STATUS_WORKING	Data is currently being transferred.

npdata_transfer_callback()

void npdata_transfer_callback

(

dmac_callback_args_t *

p_args

)

DMAC interrupt callback; unused.

Parameters

p_args

Pointer to callback arguments.

Note

This is unused and is present as a formality to enable the FSP driver to configure the interrupt; see dmac_repeat_isr.

push_data_to_buffer()

static void push_data_to_buffer ( uint32_t *const  p_block )

inlinestatic

Push new data to the secondary (or primary) buffer.

Parameters

[in]

p_block

Pointer to the block to write the data to.