Gumstix/Audiostix2 interface to LCD
Posted: June 4, 2006
Gumstix is a very neat, hobbyist-friendly embedded computer which runs Linux. It is about the size of a stick of gum (hence the name) and has a strong community support system. Various breakout and add-on boards are available making the platform versatile. I had intended to use Gumstix in my CarPC project, but I ended up spending most of my time getting the LCD to interface directly with PXA LCD driver. I have listed my findings below for the benefit of others.
Audiostix2 to LQ050Q5DR01 interface
The following table shows the connections between the Audiostix2 board and the LCD. Since the Gumstix outputs a 16-bit color (RGB565) and the LCD expects 18-bit color, we simply ground the least significant bits (LSB) of red and blue. Note that the BIAS signal is not needed for this LCD and has been left open.
GPSstix Sharp LQ050Q5DR01 My understanding -------------------------------------------------------------- LCLK PIN_3 Hsync signals the end of line PCLK PIN_13 CLK pixel clock FCLK PIN_28 Vsync signals the end of a frame LDD15 PIN_29 R5 RED_4 - Most significant bit LDD14 PIN_27 R4 RED_3 LDD13 PIN_25 R3 RED_2 LDD12 PIN_21 R2 RED_1 LDD11 PIN_19 R1 RED_0 LDD10 PIN_8 G5 GREEN_5 - Most significant bit LDD9 PIN_6 G4 GREEN_4 LDD8 PIN_4 G3 GREEN_3 LDD7 PIN_37 G2 GREEN_2 LDD6 PIN_35 G1 GREEN_1 LDD5 PIN_33 G0 GREEN_0 LDD4 PIN_24 B5 BLUE_4 - Most significant bit LDD3 PIN_22 B4 BLUE_3 LDD2 PIN_20 B3 BLUE_2 LDD1 PIN_16 B2 BLUE_1 LDD0 PIN_14 B1 BLUE_0 BIAS - Not used - PIN_1 GND - PIN_2 VCC +3.3V - PIN_5 T0 Leave open (thermistor output) - PIN_7 T1 Leave open (thermistor output) - PIN_9 HVR GND (Horiz. of vertical scan direction) - PIN_10 GND - PIN_11 GND - PIN_12 B0 GND (LSB of blue is unused) - PIN_15 GND - PIN_17 R0 GND (LSB of red is unused) - PIN_18 GND - PIN_23 GND - PIN_26 GND - PIN_30 TEST Leave open - PIN_31 GND - PIN_32 TEST Leave open - PIN_34 TEST Leave open - PIN_36 TEST Leave open - PIN_38 ENAB GND (signal to settle horiz.) - PIN_39 VCC +3.3V - PIN_40 GND
PXA Register Setup for LQ050Q5DR01
LCD Controller Control Register 0 (7-23) LCCR0 0x003008f9 00000000 00110000 00001000 11111001 LCCR0_ENB 1 LCD controller enable LCCR0_CMS 0 LCD monochrome operation enable LCCR0_SDS 0 LCD dual panel display enable LCCR0_LDM 1 LCD disable done IRQ disable LCCR0_SFM 1 LCD start of frame IRQ disable LCCR0_IUM 1 LCD fifo underrun error IRQ disable LCCR0_EFM 1 LCD end of frame IRQ disable LCCR0_PAS 1 LCD active display enable LCCR0_DPD 0 LCD send 8 pixel on L_DD[7:0] at each clock LCCR0_DIS 0 LCD controller disable LCCR0_QDM 1 LCD quick disable IRQ disable LCCR0_PDD 0 LCD palette DMA request delay LCCR0_BM 1 LCD branch start IRQ disable LCCR0_OUM 1 LCD fifo underrun IRQ disable LCD Controller Control Register 1 (7-26) LCCR1 0x46ff2d3f 01000110 11111111 00101101 00111111 LCCR1_PPL 319 LCD pixels per line (+1) LCCR1_HSW 11 LCD horizontal sync pulse width (+1) LCCR1_ELW 255 LCD end of line pixel clock wait count (+1) LCCR1_BLW 70 LCD beginning of line pixel clock wait count (+1) LCD Controller Control Register 2 (7-28) LCCR2 0x0500fcef 00000101 00000000 11111100 11101111 LCCR2_LPP 239 LCD lines per panel (+1) LCCR2_VSW 63 LCD vertical sync pulse width (+1) LCCR2_EFW 0 LCD end of frame line clock wait count (+1) LCCR2_BFW 5 LCD beginning of frame line clock wait count (+1) LCD Controller Control Register 3 (7-31) LCCR3 0x04300007 00000100 00110000 00000000 00000111 LCCR3_PCD 7 LCD pixel clock divisor (+1) LCCR3_ACB 0 LCD AC bias pin frequency (+1) LCCR3_API 0 LCD AC bias pin transitions per interrupt LCCR3_VSP 1 LCD L_FCLK vertical sync polarity active low LCCR3_HSP 1 LCD L_LCLK horizontal sync polarity active low LCCR3_PCP 0 LCD data sampled on falling edge of L_PCLK LCCR3_OEP 0 LCD L_BIAS output enable active low LCCR3_BPP 16 LCD bits per pixel LCCR3_DPC 0 LCD double pixel clock rate at L_PCLK
Sample Framebuffer Code
The C code below can be used to check the dimensions & depth of your framebuffer device. Additionally, it prints a couple of tests patterns to screen. If you happen to have a 16-bit display and have downloaded the following raw image, then you will also see a picture being printed to screen.
/images/taj.raw
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>
#define RGB565(r,g,b) (((r >> 3) & 31) << 11) | (((g >> 2) & 63) << 5) | ((b >> 3) & 31)
/* structures for retrieving framebuffer information */
struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;
/* size of video memory in bytes */
long int screensize;
/* pointer to memory mapped framebuffer */
char *fbp;
/*
* Function to set a pixel in framebuffer with the specified
* (r,g,b). Works only with 32bpp and 16bpp modes.
*/
void set_pixel(int x, int y, unsigned char r, unsigned char g, unsigned char b)
{
long int location;
location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
(y+vinfo.yoffset) * finfo.line_length;
if ( vinfo.bits_per_pixel == 32 ) {
*(fbp + location) = b;
*(fbp + location + 1) = g;
*(fbp + location + 2) = r;
*(fbp + location + 3) = 0;
} else { //assume 16bpp
*((unsigned short int*)(fbp + location)) = RGB565(r,g,b);
}
}
/*
* Program entry point. Opens /dev/fb0 and prints two patterns
* to it.
*/
int main()
{
int fd, fbfd, x, y;
unsigned char r, g, b;
/* Open the file for reading and writing */
fbfd = open("/dev/fb0", O_RDWR);
if (fbfd == -1) {
perror("/dev/fb0");
exit(1);
}
/* Get fixed screen information */
if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
perror("FBIOGET_FSCREENINFO");
exit(2);
}
/* Get variable screen information */
if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
perror("FBIOGET_VSCREENINFO");;
exit(3);
}
printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel );
/* Figure out the size of the video memory in bytes */
screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
/* Map the device to memory */
fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
fbfd, 0);
if ((int)fbp == -1) {
perror("mmap()");
exit(4);
}
printf("Turning screen red...\n");
for ( y = 20; y < vinfo.yres-20; y++ )
for ( x = 20; x < vinfo.xres-20; x++ )
set_pixel(x, y, 255, 0, 0);
sleep(2);
printf("Turning screen green...\n");
for ( y = 20; y < vinfo.yres-20; y++ )
for ( x = 20; x < vinfo.xres-20; x++ )
set_pixel(x, y, 0, 255, 0);
sleep(2);
printf("Turning screen blue...\n");
for ( y = 20; y < vinfo.yres-20; y++ )
for ( x = 20; x < vinfo.xres-20; x++ )
set_pixel(x, y, 0, 0, 255);
/* PATTERN #1: something funky */
sleep(2);
printf("Printing pattern #1...\n");
for ( y = 0; y < vinfo.yres; y++ )
for ( x = 0; x < vinfo.xres; x++ )
set_pixel(x, y, 31-(y-100)/16, (x-100)/6, 10);
sleep(2);
/* Blank the screen */
memset(fbp, '\0', screensize);
/* PATTERN #2: vertical and horizontal lines at 1/3 and 2/3 */
printf("Printing pattern #2...\n");
for ( y = 0; y < vinfo.yres; y++ ) {
set_pixel(2*vinfo.xres/3, y, 255, 255, 255);
set_pixel(vinfo.xres/3, y, 255, 255, 255);
}
for ( x = 0; x < vinfo.xres; x++ ) {
set_pixel(x, 2*vinfo.yres/3, 255, 255, 255);
set_pixel(x, vinfo.yres/3, 255, 255, 255);
}
sleep(2);
printf("Printing pictures...\n");
fd = open("taj.raw", O_RDONLY);
if (fd == -1)
perror("taj.raw");
else
{
for ( y = 0; y < 213; y++ )
for ( x = 0; x < 320; x++ )
{
read(fd, &r, 1);
read(fd, &g, 1);
read(fd, &b, 1);
set_pixel(x, y, r, g, b);
}
close(fd);
}
printf("Done\n");
munmap(fbp, screensize);
close(fbfd);
return 0;
}