Rockchip Android BOX display framework configuration

Source:RK-SM-YF-504 V1.0.1,Chinese. This covers user resolution,scaling,color and BCSH settings plus framebuffer resolution and primary/secondary display configuration for the documented BOX SDK. Product scope:RK3328/RK3368/RK3229,Linux4.4/Linux4.19,Android8.1+. No ArmSoM validation or confirmation for every later SDK is implied;no source commands executed. All six figures are CN originals,no EN source supplied.

1 Display settings

1.1 Display settings flow

The documented Android8.1+ RK platform uses DRM (Direct Rendering Manager). Upper interfaces configure DRM parameters;HWC ultimately applies them through libdrm. The diagram shows TVSetting → rkdisplay → HWC → libdrm → kernel.

Display settings flow - Original source figure; PDF page 5 (CN).

1.2 Resolution filtering

The initial list can contain many unwanted modes. HWC filters hot-pluggable HDMI/DP display modes with device/rockchip/common/resolution_white.xml before passing them upward. Each <resolution> block specifies one allowed mode. Timing items refer to the original diagram below.

DRM_MODE_FLAG_PHSYNC (1<<0)
DRM_MODE_FLAG_NHSYNC (1<<1)
DRM_MODE_FLAG_PVSYNC (1<<2)
DRM_MODE_FLAG_NVSYNC (1<<3)
DRM_MODE_FLAG_INTERLACE (1<<4)

Resolution timing definitions - Original source figure; PDF page 6 (CN).

2 Baseparameter partition

2.1 Baseparameter image

Display settings are stored in the1MB Baseparameter partition,initialized by flashing baseparameter.img. The SDK default is device/rockchip/common/baseparameter/baseparameter_fb1080.img. Generate a replacement using saveBaseParameter and set TARGET_BASE_PARAMETER_IMAGE in BoardConfig.mk,for example:

TARGET_BASE_PARAMETER_IMAGE := device/rockchip/rk3328/baseparameter.img

2.2 saveBaseParameter

This tool inspects,sets and exports the partition. Source:device/rockchip/common/baseparameter/saveBaseParameter. eng/userdebug builds include it by default;run it on the device. -h prints help,-p prints partition data,-t <path> exports an image that can be pulled to the host and flashed. The original help lists these additional options:

saveBaseParameter help - Original source figure; PDF page 7 (CN).

Partition data example - Original source figure; PDF page 8 (CN).

The basic area receives user settings. Factory reset erases that area and copies the backup area into it. Both areas contain primary and auxiliary display data:resolution,color,fbinfo (framebuffer resolution),device,bcsh (Brightness,Contrast,Saturation,Hue),overscan (left,top,right,bottom order) and feature (special flags). Note the CLI overscan order differs from the struct member order below.

2.3 Partition data structures

2.3.1 Partition layout

struct disp_info{
struct drm_display_mode resolution;
struct overscan scan;
enum output_format format;
enum output_depth depthc;
unsigned int feature;
struct hwc_inital_info hwc_info;
struct bcsh_info bcsh;
unsigned int reserve[128];
struct lut_data mlutdata;
};

struct disp_info main;
struct disp_info aux;

main occupies the first8KB address range;aux starts at offset8KB. sizeof(disp_info) is not8KB,so read/write the records separately and seek8KB before auxiliary access. The diagram labels drm_display_mode52B,overscan12B,format4B,depth4B,feature4B,hwc_inital_info140B,bcsh8B,reserve512B,lut_data6KB+4. These are source-diagram labels,not a verified ABI:the shown lut_data has a16-bit size and three1024-entry16-bit arrays,so confirm alignment/layout against actual SDK headers.

Main/aux partition layout - Original source figure; PDF page 9 (CN).

2.3.2 disp_info fields

drm_display_mode stores resolution timing;clock is in kHz. overscan stores scaling limits and edge values.

struct drm_display_mode {
/* Proposed mode values */
int clock; /* in kHz */
int hdisplay;
int hsync_start;
int hsync_end;
int htotal;
int vdisplay;
int vsync_start;
int vsync_end;
int vtotal;
int vrefresh;
int vscan;
unsigned int flags;
int picture_aspect_ratio;
};

struct overscan {
unsigned int maxvalue;
unsigned short leftscale;
unsigned short rightscale;
unsigned short topscale;
unsigned short bottomscale;
};

output_format selects color format. Property string Auto selects output_ycbcr_high_subsampling. The high preference is YCbCr444 > YCbCr422 > YCbCr420 > RGB;low preference reverses that order. output_depth selects bit depth;Auto selects Automatic.

enum output_format {
output_rgb=0,
output_ycbcr444=1,
output_ycbcr422=2,
output_ycbcr420=3,
output_ycbcr_high_subsampling=4, // (YCbCr444 > YCbCr422 > YCbCr420 > RGB)
output_ycbcr_low_subsampling=5 , // (RGB > YCbCr420 > YCbCr422 > YCbCr444)
invalid_output=6,
};

enum output_depth{
Automatic=0,
depth_24bit=8,
depth_30bit=10,
};

feature controls automatic resolution/color,HDCP1.x and resolution whitelist filtering. hwc_inital_info configures framebuffer width/height,fps and attached primary/auxiliary devices. device example:HDMI-A,TV;fps can limit frame rate.

#define RESOLUTION_AUTO (1<<0)
#define COLOR_AUTO (1<<1)
#define HDCP1X_EN (1<<2)
#define RESOLUTION_WHITE_EN (1<<3)

struct hwc_inital_info{
char device[128];
unsigned int framebuffer_width;
unsigned int framebuffer_height;
float fps;
};

bcsh_info values range0–100,all default50. reserve[128] is reserved for future use. lut_data stores RGB lookup tables;size is the number of values in each table,maximum1024.

struct bcsh_info {
unsigned short brightness;
unsigned short contrast;
unsigned short saturation;
unsigned short hue;
};

unsigned int reserve[128];

struct lut_data{
uint16_t size;
uint16_t lred[1024];
uint16_t lgreen[1024];
uint16_t lblue[1024];
};

2.3.3 Backup area

The second half starts at512KB and preserves initial settings for factory reset. The diagram places main_backup and AUX_backup in the first16KB of that half,with the same8KB separation.

Backup layout - Original source figure; PDF page 11 (CN).

2.4 Debug information

Use logcat | grep BP to check whether HWC read Baseparameter correctly at boot.

logcat | grep BP

2.5 FAQ:1280×720 framebuffer

Source procedure:a)get root;b)reset partition;c)write settings;d)print and confirm;e)export image and pull it to the host. Warning:-R2 resets the partition including backup;back up the existing data before applying this example. The following commands are documentary,not executed here.

su
saveBaseParameter -R 2
saveBaseParameter -d 0 -f 1280x720@60 -D "HDMI-A,TV" -c Auto -u 2 -o "100,100,100,100" -b "50,50,50,50"
saveBaseParameter -p
saveBaseParameter -t /sdcard/baseparameter.img
adb pull /sdcard/baseparameter.img

f)Flash the generated baseparameter.img,reboot and inspect logcat | grep BP to confirm HWC values. g)Place the image in the SDK,for example device/rockchip/rk3328/baseparameter.img,apply the following BoardConfig change and rebuild. The source wrapped the added assignment over two printed lines;it is joined below as one Make assignment.

diff --git a/rk3328_box/BoardConfig.mk b/rk3328_box/BoardConfig.mk
index 3831ce8..f151fe7 100755
--- a/rk3328_box/BoardConfig.mk
+++ b/rk3328_box/BoardConfig.mk
@@ -16,6 +16,8 @@
TARGET_BOARD_PLATFORM_PRODUCT := box
+TARGET_BASE_PARAMETER_IMAGE := device/rockchip/rk3328/baseparameter.img
+
# Use the non-open-source parts, if they're present
-include vendor/rockchip/rk3328/BoardConfigVendor.mk
-include device/rockchip/common/BoardConfig.mk