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echoplayer: add shadow framebuffer to avoid tearing

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Using a simple memcpy to a separate framebuffer prevents
objectionable levels of flickering caused by scanning out
the main framebuffer while it's modified between updates.

With optimized memcpy, copying the whole framebuffer takes
about 260us at maximum CPU+bus frequency. Using DMA would
likely be a bit faster and more power-efficient, but that
can be left as a future optimization.

Change-Id: Ia6dc36d797cdb7a5f6663078c0ecce661267bedf
This commit is contained in:
Aidan MacDonald 2026-01-24 21:26:00 +00:00 • committed by Solomon Peachy
parent 7adb9cd1b4
commit ad9471be3b
1 changed files with 12 additions and 3 deletions
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15
firmware/target/arm/stm32/echoplayer/lcd-echoplayer.c
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@ -30,6 +30,7 @@
#include "regs/stm32h743/rcc.h"
#include "regs/stm32h743/spi.h"
#include "regs/stm32h743/ltdc.h"
#include <string.h>
#define MS_TO_TICKS(x) \
(((x) + (1000 / HZ - 1)) / (1000 / HZ))
@ -60,7 +61,8 @@ struct stm_spi_config spi_cfg = {
.hw_cs_output = true,
};
struct stm_spi spi;
static struct stm_spi spi;
static fb_data shadowfb[LCD_WIDTH*LCD_HEIGHT] IRAM_LCDFRAMEBUFFER;
enum lcd_controller_state
{
@ -101,7 +103,7 @@ static void enable_ltdc(void)
reg_assignf(LTDC_LAYER_WHPCR(0), WHSPPOS(ahbp + LCD_HAW), WHSTPOS(ahbp + 1));
reg_assignf(LTDC_LAYER_WVPCR(0), WVSPPOS(avbp + LCD_VAH), WVSTPOS(avbp + 1));
reg_assignf(LTDC_LAYER_PFCR(0), PF(BV_LTDC_LAYER_PFCR_PF_RGB565));
reg_var(LTDC_LAYER_CFBAR(0)) = (uintptr_t)FBADDR(0, 0);
reg_var(LTDC_LAYER_CFBAR(0)) = (uintptr_t)&shadowfb[0];
reg_assignf(LTDC_LAYER_CFBLR(0), CFBP(row_bytes), CFBLL(row_bytes + 7));
reg_assignf(LTDC_LAYER_CFBLNR(0), CFBLNBR(LCD_HEIGHT));
reg_assignf(LTDC_LAYER_CR(0), LEN(1));
@ -244,6 +246,8 @@ void lcd_update(void)
if (!lcd_active())
return;
/* TODO: optimize using DMA2D */
memcpy(shadowfb, FBADDR(0, 0), sizeof(shadowfb));
commit_dcache();
}
@ -268,8 +272,13 @@ void lcd_update_rect(int x, int y, int width, int height)
if (height > LCD_HEIGHT - y)
height = LCD_HEIGHT - y;
/* TODO: optimize using DMA2D */
for (int dy = 0; dy < height; ++dy)
commit_dcache_range(FBADDR(x, y+dy), FB_DATA_SZ * width);
{
fb_data *shaddr = &shadowfb[(y+dy)*LCD_WIDTH + x];
memcpy(shaddr, FBADDR(x, y+dy), FB_DATA_SZ * width);
commit_dcache_range(shaddr, FB_DATA_SZ * width);
}
}
void spi5_irq_handler(void)