Hello, and welcome to this presentation of the STM32 Chrom

Hello, and welcome to this presentation of the STM32 Chrom
Hello, and welcome to this presentation of the STM32
Chrom-ART Accelerator™. It covers the features of this
of this adaptive real-time accelerator block, which is
widely used for graphic computing in the microcontroller.
The Chrom-ART accelerator offers true hardware
acceleration for graphical operations.
The Chrom-ART accelerator is built around a 2D DMA
engine for fast data copy with specific functions to
support pixel format conversion as well as blending
operations between two planes. It also provides specific
modes for managing anti-aliased fonts.
The Chrom-ART accelerator will offload the CPU for
most of the graphical operations with a one pixel per
cycle throughput, integrated pixel format conversion and
The Chrom-ART accelerator is fully integrated in
graphical stacks making its software integration
transparent to the user.
The Chrom-ART accelerator has four operating modes.
- Register-to-memory for rectangle filling operations,
- Memory-to-memory for 2D memory copy operations,
- Memory-to-memory with pixel format conversion for
bitmap drawing with format conversion,
- Memory-to-memory with pixel format conversion and
blending for bitmap or text drawing with transparency.
The user can program independently all the parameters for
the source and the destination:
- The address of the layer including its size and position
- The color format
- The way transparency is managed.
Register-to-memory mode is used to fill a part or whole
destination image with a specific color.
The color value is set in a register of the output PFC.
Memory-to-memory mode is used to copy a part or whole
source image into a part or whole destination image without
changing the color format.
Memory-to-memory mode with pixel format conversion is
used to do the same type of copy as Memory-to memory
mode but with a pixel format conversion. It can copy an
RGB565 image into an RGB888 image without having to
use the CPU.
Memory-to-memory mode with pixel format conversion
and blending is used to blend a part or whole source
image with a part or whole destination image with a
different pixel format. This is widely used to draw bitmap
icons having transparency or fonts.
For each foreground and background layer, the format
can be programmed independently.
Direct mode fetches the RGB or ARGB content directly
from the memory.
Indirect mode uses an intermediate color look-up table to
determine the color to be used during the copy or
blending operation.
All the input color modes are transformed internally into
ARGB8888 format to perform the blending operation.
Specific modes can be used to efficiently manage texts and
Only the transparency value is stored in memory for
rendering anti-aliased fonts.
The color is added during the pixel format conversion
process and can be programmed by the user.
These modes are very efficient for storing high-quality
bitmap fonts.
The output pixel format converter generates the color for the
destination independently from the source.
There is no indirect mode in output as this would imply to
calculate a color look-up table (CLUT).
Nevertheless, memory-to-memory operations without Pixel
Format Conversion (PFC) can copy data independently of
their formats.
The fully hardware blender allows to blend a foreground
image and a background image with transparency.
This can be used to draw bitmap images of any shape
with a perfect rendering.
1 pixel is generated per cycle making this complex operation
much more efficient than if it was done by the CPU.
The resulting pixel can be coded independently from the
source thanks to the output pixel format converter.
The output configuration defines the working area for the
Chrom-ART operation.
The address and the line offset parameters are used to
select which sub-area of the output is concerned.
The background and foreground layers have their own
configuration for address, line offset and color format.
This defines which area of the foreground and background
layers are targeted by the Chrom-ART operations.
The Chrom-ART accelerator has 6 interrupt sources to
- Configuration errors
- CLUT transfer complete
- CLUT access error
- Watermark reached during a transfer
- Transfer complete
- Transfer error
No DMA trigger is used as the Chrom-ART accelerator
embeds its own DMA.
The Chrom-ART accelerator is active in Run and Sleep
modes. A Chrom-ART interrupt can cause the device to
exit Sleep mode. In Stop mode, the Chrom-ART
accelerator is frozen and its registers content is kept. In
Standby mode, the Chrom-ART accelerator is powereddown and it must be reinitialized afterwards.
The Chrom-ART accelerator is widely used in any
graphical application to compute the frame buffer without
any CPU load and with a very efficient throughput.
It can compose the whole scene with transparency and
facilitate the management of animations.
Text rendering is also accelerated, making it easy and
efficient to manage anti-aliased fonts.
You can refer to the trainings related to the RCC and
interrupts for additional information.
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