AM3352 24-bit mode LCD

N Luna

Hi,

In the AM335x silicon errata (http://www.ti.com/lit/er/sprz360f/sprz360f.pdf), the 16 bit mode LCD is RGB and in 24 bit mode the LCD is BGR. Is it correct ?

I adapted board-am335xevm.c to support my new screen (I'm using beaglebone black with custom CAPE) and the red and blue colors are swapped.

Here's what I added in the board specific file:

static const struct display_panel disp_panel = {
WVGA,
24,
24,
COLOR_ACTIVE,
};

static struct lcd_ctrl_config lcd_cape_cfg = {
&disp_panel,
.ac_bias = 255,
.ac_bias_intrpt = 0,
.dma_burst_sz = 16,
.bpp = 24,
.fdd = 0x80,
.tft_alt_mode = 1,
.stn_565_mode = 0,
.mono_8bit_mode = 0,
.invert_line_clock = 1,
.invert_frm_clock = 1,
.sync_edge = 0,
.sync_ctrl = 0,
.raster_order = 0,
};

Our custom CAPE is routed as stated in the errata..

Am I missing something ?

Thank you !

Best regards,

over 11 years ago

0 Biser Gatchev-XID over 11 years ago

TI__Guru**** 393215 points

How many bits is your LCD? 16 or 24? BB Black has only 16 bits pinned out. You probably need to switch your LCD mode from RGB888 to RGB565 or vice versa.

0 N Luna over 11 years ago in reply to Biser Gatchev-XID

Intellectual 740 points

It is 18 bits. On the AM335x we used 6 bits (MSB) of each color.

On the BB Black you can you LCD16 to LCD23, but they are not named that way on the connector (J1 and J2). I changed the pinmux in my board specific file so I think that should be OK ?

I'm trying to use the LCD mode RGB888.

Regards,

0 Biser Gatchev-XID over 11 years ago in reply to N Luna

TI__Guru**** 393215 points

The net names on the BB Black are:

EHRPWM2A - corresponds to LCD_DATA23

EHRPWM2B - corresponds to LCD_DATA22

GPIO0_26 - corresponds to LCD_DATA21

GPIO0_27 - corresponds to LCD_DATA20

GPIO1_12 - corresponds to LCD_DATA19

GPIO1_13 - corresponds to LCD_DATA18

GPIO1_14 - corresponds to LCD_DATA17

GPIO1_15 - corresponds to LCD_DATA16

If you changed the pinmux you should be OK. Colors will correspond to Errata figure 2. For 18-bit display you should leave LCD_DATA[23:18] not connected.

0 N Luna over 11 years ago in reply to Biser Gatchev-XID

Intellectual 740 points

Hi,

Yes we are using those nets and LCD_DATA[23:18] are not connected. Blue and Red are swapped.

I wonder if:

1- The code I added in the board specific file is good and if I correctly configured the LCD unit in 24 bpp. (see code in first post)

2- The pinout for 24 bpp mode LCD is good in the errata ?

Regards,

0 Biser Gatchev-XID over 11 years ago in reply to N Luna

TI__Guru**** 393215 points

1. I can't say about code, but bit 25 (tft24) in the RASTER_CTRL Register should be set to 1.

2. Yes, the errata is correct.

0 N Luna over 11 years ago in reply to Biser Gatchev-XID

Intellectual 740 points

Hi,

bit 25 (tft24) in the RASTER_CTRL is set to one:

./mem_io -4 -l 4 -r 0x4830e028
4830e028: 02a80081

Do you think I need to swap anything in the driver (da8xx-fb.c) ?

Thank you

0 N Luna over 11 years ago in reply to N Luna

Intellectual 740 points

Here's the pinout used.

Do you see anything wrong ?

Thank you !

Regards,

0 N Luna over 11 years ago in reply to N Luna

Intellectual 740 points

I solved the problem, but I still don't understand why I needed to change something in the driver.

In da8xx-fb.c function fb_check_var I changed

case 24:
/*
var->red.offset = 16;
var->red.length = 8;
var->green.offset = 8;
var->green.length = 8;
var->blue.offset = 0;
var->blue.length = 8; */

var->red.offset = 0;
var->red.length = 8;
var->green.offset = 8;
var->green.length = 8;
var->blue.offset = 16;
var->blue.length = 8;

break;

The colors on the LCD are now OK, but I'm interested to know if this is a known issue ?

Regards.

0 ozgur ozer over 8 years ago in reply to N Luna

Prodigy 10 points

no, this is not. Red and Blue colors is OK but SGX driver is not working correctly. red and blue offset 16 - 0 OK but
0 - 16 ; "omaplfb: OMAPLFBInitFBDev: Device 0: Unknown FB format" and OpenGL not working.

Processors

Processors forum

AM3352 24-bit mode LCD