NXP¶

NXP has integrated LVGL into the MCUXpresso SDK packages for general purpose and crossover microcontrollers, allowing easy evaluation and migration into your product design. Download an SDK for a supported board today and get started with your next GUI application.

Creating new project with LVGL¶

Downloading the MCU SDK example project is recommended as a starting point. It comes fully configured with LVGL (and with PXP/VGLite support if the modules are present), no additional integration work is required.

HW acceleration for NXP iMX RT platforms¶

Depending on the RT platform used, the acceleration can be done by NXP PXP (PiXel Pipeline) and/or the Verisilicon GPU through an API named VGLite. Each accelerator has its own context that allows them to be used individually as well simultaneously (in LVGL multithreading mode).

PXP accelerator¶

Several drawing features in LVGL can be offloaded to the PXP engine. The CPU is available for other operations while the PXP is running. RTOS is required to block the LVGL drawing thread and switch to another task or suspend the CPU for power savings.

Supported draw callbacks are available in "src/draw/nxp/pxp/lv_draw_pxp.c":

    pxp_draw_ctx->base_draw.draw_img_decoded = lv_draw_pxp_img_decoded;
    pxp_draw_ctx->blend = lv_draw_pxp_blend;
    pxp_draw_ctx->base_draw.wait_for_finish = lv_draw_pxp_wait_for_finish;
    pxp_draw_ctx->base_draw.buffer_copy = lv_draw_pxp_buffer_copy;

Features supported:¶

All operations can be used in conjunction with optional transparency.

RGB565 and ARGB8888 color formats
Area fill with color
BLIT (BLock Image Transfer)
Screen Rotation (90, 180, 270 degree)
Color keying
Recoloring (color tint)
Image Rotation (90, 180, 270 degree)
Buffer copy
RTOS integration layer
Default FreeRTOS and bare metal code provided
Combination of recolor and/or rotation + color key/alpha blend/transparency is supported. That is achieved by PXP in two steps:
- First step is to recolor/rotate the image to a temporary buffer (statically allocated)
- Second step is required to handle color keying, alpha channel or to apply transparency

Known limitations:¶

Rotation is not supported for images unaligned to blocks of 16x16 pixels. PXP is set to process 16x16 blocks to optimize the system for memory bandwidth and image processing time. The output engine essentially truncates any output pixels after the desired number of pixels has been written. When rotating a source image and the output is not divisible by the block size, the incorrect pixels could be truncated and the final output image can look shifted.

Basic configuration:¶

Select NXP PXP engine in lv_conf.h: Set LV_USE_GPU_NXP_PXP to 1
Enable default implementation for interrupt handling, PXP start function and automatic initialization: Set LV_USE_GPU_NXP_PXP_AUTO_INIT to 1
If SDK_OS_FREE_RTOS symbol is defined, FreeRTOS implementation will be used, otherwise bare metal code will be included

Basic initialization:¶

If LV_USE_GPU_NXP_PXP_AUTO_INIT is enabled, no user code is required; PXP is initialized automatically in lv_init()
For manual PXP initialization, default configuration structure for callbacks can be used. Initialize PXP before calling lv_init()

      #if LV_USE_GPU_NXP_PXP
        #include "src/draw/nxp/pxp/lv_gpu_nxp_pxp.h"
      #endif
      . . .
      #if LV_USE_GPU_NXP_PXP
        PXP_COND_STOP(!lv_gpu_nxp_pxp_init(), "PXP init failed.");
      #endif

Project setup:¶

Add PXP related files to project:
- src/draw/nxp/pxp/lv_draw_pxp.c[.h]: draw context callbacks
- src/draw/nxp/pxp/lv_draw_pxp_blend.c[.h]: fill and blit (with optional transformation)
- src/draw/nxp/pxp/lv_gpu_nxp_pxp.c[.h]: init, uninit, run/wait PXP device
- src/draw/nxp/pxp/lv_gpu_nxp_pxp_osa.c[.h]: OS abstraction (FreeRTOS or bare metal)
  - optional, required only if LV_USE_GPU_NXP_PXP_AUTO_INIT is set to 1
PXP related code depends on two drivers provided by MCU SDK. These drivers need to be added to project:
- fsl_pxp.c[.h]: PXP driver
- fsl_cache.c[.h]: CPU cache handling functions

Logging:¶

By default, LV_GPU_NXP_PXP_LOG_ERRORS is enabled so that any PXP error will be seen on SDK debug console
By default, LV_GPU_NXP_PXP_LOG_TRACES is disabled. Enable it for tracing logs (like PXP limitations)

Advanced configuration:¶

Implementation depends on multiple OS-specific functions. The struct lv_nxp_pxp_cfg_t with callback pointers is used as a parameter for the lv_gpu_nxp_pxp_init() function. Default implementation for FreeRTOS and bare metal is provided in lv_gpu_nxp_pxp_osa.c
- pxp_interrupt_init(): Initialize PXP interrupt (HW setup, OS setup)
- pxp_interrupt_deinit(): Deinitialize PXP interrupt (HW setup, OS setup)
- pxp_run(): Start PXP job. Use OS-specific mechanism to block drawing thread. PXP must finish drawing before leaving this function.
Area threshold (size limit) is configurable and used to decide whether the area will be processed by PXP or not. Areas smaller than the defined value will be processed by CPU and those bigger than the threshold will be processed by PXP. The threshold is defined as a macro in lv_draw_pxp.c
- LV_GPU_NXP_PXP_SIZE_LIMIT: size threshold for fill/blit (with optional transformation)

VGLite accelerator¶

Extra drawing features in LVGL can be handled by the VGLite engine. The CPU is available for other operations while the VGLite is running. An RTOS is required to block the LVGL drawing thread and switch to another task or suspend the CPU for power savings.

Supported draw callbacks are available in "src/draw/nxp/vglite/lv_draw_vglite.c":

    vglite_draw_ctx->base_draw.init_buf = lv_draw_vglite_init_buf;
    vglite_draw_ctx->base_draw.draw_line = lv_draw_vglite_line;
    vglite_draw_ctx->base_draw.draw_arc = lv_draw_vglite_arc;
    vglite_draw_ctx->base_draw.draw_rect = lv_draw_vglite_rect;
    vglite_draw_ctx->base_draw.draw_img_decoded = lv_draw_vglite_img_decoded;
    vglite_draw_ctx->blend = lv_draw_vglite_blend;
    vglite_draw_ctx->base_draw.wait_for_finish = lv_draw_vglite_wait_for_finish;
    vglite_draw_ctx->base_draw.buffer_copy = lv_draw_vglite_buffer_copy;