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SAMA5D4-EK LCDC: Adding a delay after enabling the LCD solves lots of start-up timing issues

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This commit is contained in:
Gregory Nutt 2014-07-12 08:05:22 -06:00
parent 58ab6ec03f
commit 253110bbf1
2 changed files with 24 additions and 1 deletions
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14
arch/arm/src/sama5/sam_lcd.c
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@ -1,7 +1,7 @@
/****************************************************************************
* arch/arm/src/sama5/sam_lcd.c
*
* Copyright (C) 2013 Gregory Nutt. All rights reserved.
* Copyright (C) 2013-2014 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* References:
@ -2973,6 +2973,18 @@ int up_fbinitialize(void)
sam_show_hcr();
#endif
#if defined(BOARD_LCDC_ENABLE_DELAY) && BOARD_LCDC_ENABLE_DELAY > 0
/* Delay a bit after enabling the LDC. I presume that a delay of a few
* frame times allows some unstable clocking to synchronize before we
* tart thrashing the framebuffer? But I am not sure why this is
* necessary and, in fact, is certainly not necessary in most LCDC
* configurations. Perhaps this delay would not be necessary if timings
* were more precise?
*/
usleep(BOARD_LCDC_ENABLE_DELAY);
#endif
/* Enable the backlight.
*
* REVISIT: Backlight level could be dynamically adjustable

11
configs/sama5d4-ek/include/board.h
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@ -203,6 +203,17 @@
#define BOARD_LCDC_PIXELCLOCK \
(BOARD_LCDC_HSPERIOD * BOARD_LCDC_VSPERIOD * BOARD_LCDC_FRAMERATE)
/* This specifies a delay after enabling the LCDC. This was found
* experimentally and is very much a kludge. I presume that a delay of a
* couple of frame times allows some unstable clocking to synchronize before
* we start thrashing the framebuffer? But I am not sure why this is
* necessary and, in fact, is certainly not necessary in other LCDC
* configurations. Perhaps the delay would not be necessary if timings were
* more precise?
*/
#define BOARD_LCDC_ENABLE_DELAY (50*1000)
/* Backlight prescaler value and PWM output polarity */
#define BOARD_LCDC_PWMPS LCDC_LCDCFG6_PWMPS_DIV1