12. System performance measurements

For the whole system evaluation, a test application was created that run for different physical connection LCD interfaces, various color formats using one or two LCDC HW layer and different number of frame buffers. The test application splits the display vertically into half and draws a bitmap, stored at the external Flash, using 0x80 as alpha value for transparency, at the first half and a rectangle, filled with color, at the second half. As the System Performance Metrics table denotes, with regards to the measured FPS, the system has high performance for Bands and Low end watches. The FPS in most of those cases is larger than 40. For the high end watches, where the output color should be high enough for better image quality, the size of the FB is almost 800kB and the FPS drops below 20. The FPS, could be increased, almost doubled, by lowering the output color format and make use of 1 Layer with 2 FB but the required size of the FBs, should be taken into significant account.

Variable	Value
Resolution	120 x 240
	150 x 480
	320 x 320
	550 x 450
Layers Number	1
	2
Layer Location	SRAM Layer0 when using 1 Layer, and Layer1 when using 2 Layers
	Storage FLASH Layer0 ONLY when using 2 Layers
FB Number	1
	2
FB Color Format	16 bit (when output color format is 16 bit)
	32 bit (when output color format is 24 bit)
FB Location	System RAM
Output Color Format	16 bit
	24 bit
Resources Format	32 bit
Resources Location	Storage Flash
Display refresh period (msec)	1
LCDC Interface	SPI4
	DSPI
	QSPI
LCDC Prefetch Level	LVL3 (Wait until at least 116 bytes have been inserted at the LCDC FIFO)
LCDC burst length	16
LCDC blend mode	HW_LCDC_BL_SIMPLE
GPU burst length	8 beat

Table 17 Test Application Configuration Parameters

Layers	FBs	Layers in	FB1	FB2	Resolution 150 x 480 (Band)		Resolution 320 x 320 (Low End Watch)		Resolution 320 x 320 (Low End Watch)		Resolution 450 x 450 (High End Watch)		Resolution 450 x 450 (High End Watch)
Output Color Format (bit)					24		16		24		16		24
System Clock (MHz)					96	160	96	160	96	160	96	160	96	160
1	2	SRAM	SRAM	SRAM	59.2	60.8	57.1	55.5	49.3	51.7	38.2	37.4	RAM overflow	RAM overflow
1	1	SRAM	SRAM	N/A	40.5	38.5	39.0	36.5	31.9	29.9	23.7	21.9	18.7	17.3
2	2	SRAM & FLASH	SRAM	SRAM	48.8	43.8	N/A	N/A	37.2	31.2	N/A	N/A	RAM overflow	RAM overflow
2	1	SRAM & FLASH	SRAM	N/A	39.9	37.7	N/A	N/A	31.6	29.6	N/A	N/A	18.6	17.5

Table 18 System Performance Metrics for QSPI interface

Note

When using 16-bit as output color, the input color format of the FB is 16-bit also. In those cases, no alpha value exists so there is not point of using 2 HW Layers for blending purposes. As a result, the scenarios with 16-bit output color format and 2 LCDC Layers are marked as Not Applicable.