GP2X Writing To The Screen From The 940


Orkie

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I've started writing an application which will run purely on the 940 in the end (I was bored ;)) and I used the main.c/code.c layout and Makefile from Dzz's demo tutorials, with my own loader using rlyeh's minimal library. I have found my way around the registers so far, but writing to the screen seems to be more difficult.

CODE
#include <stdint.h>
#define mem2addr(a) (a-0x2000000)
unsigned short *memregs16;
uint16_t *screen, *fb0, *fb1;

void fb_flip(uint32_t fb_addr)
{
memregs16[0x290E>>1] = (uint16_t)(fb_addr & 0xffff);
memregs16[0x2910>>1] = (uint16_t)(fb_addr >> 16);
fb_addr += 640;
memregs16[0x2912>>1] = (uint16_t)(fb_addr & 0xffff);
memregs16[0x2914>>1] = (uint16_t)(fb_addr >> 16);
}

void flip() {
if(screen == fb0) fb_flip((uint32_t) fb1);
else fb_flip((uint32_t) fb0);
}

void vsync(void) {
while(memregs16[0x1182>>1]&(1<<4)); // waiting for V-sync
}

void Do940Stuff()
{
// Set up registers
memregs16 = (unsigned short*)mem2addr(0xC0000000);
fb0 = (uint16_t*)mem2addr(0x03101000);
fb1 = (uint16_t*)mem2addr(0x03381000);
screen = fb0;
memregs16[0x28DA>>1] = 0x004AB; // 16bpp, only region 1 activated

memregs16[0x290C>>1] = 640; // in 16bpp mode, this means width = 320

unsigned int loop;

while(1) {
vsync();
for(loop = 76800; loop--; ) {
screen[loop] = 0xF800;
}
flip();
}
}



This in code.c finally displays something (took me ages to get anything on-screen) but it looks like pink static. It *should* fill the screen in a solid red colour. Any ideas what I can do to fix this?

Here is a binary so you can see the problem for yourself: http://x11.gp2x.de/tempfiles/940ldr.zip

Thanks
 

notaz

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You don't need to do mem2addr() for addresses you pass to fb_flip(), display controller (or whatever fetches framebuffer from memory) sees the address space the same way as 920, not as 940.
 

Orkie

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I've now got the following, but I still get a static background with horizontal bars of a different kind of static. But now, I get a flickering screen too (possibly I'm blitting at the wrong time).

CODE

#include <stdint.h>
#define mem2addr(a) (a-0x2000000)
volatile uint16_t *memregs16;
#define PHYSICAL_SCREEN0 0x3100000

#define PHYSICAL_SCREEN1 0x3180000
volatile uint16_t *screen;
volatile uint16_t *fb0;
volatile uint16_t *fb1;
int current_screen = 0;

void fb_flip(uint32_t fb_addr)
{
memregs16[0x2912>>1] = (uint16_t)(fb_addr & 0xffff);
memregs16[0x2914>>1] = (uint16_t)(fb_addr >> 16);
}

void flip(void) {
//if(screen == fb0) fb_flip((uint32_t) fb1);
//else fb_flip((uint32_t) fb0);
if(current_screen == 0) {
memregs16[0x290E>>1] = memregs16[0x2912>>1] =

(unsigned short) (PHYSICAL_SCREEN0 & 0xFFFF);

memregs16[0x2910>>1] = memregs16[0x2914>>1] =

(unsigned short) (PHYSICAL_SCREEN0 >> 16);

current_screen = 1;
} else {
memregs16[0x290E>>1] = memregs16[0x2912>>1] =

(unsigned short) (PHYSICAL_SCREEN1 & 0xFFFF);

memregs16[0x2910>>1] = memregs16[0x2914>>1] =

(unsigned short) (PHYSICAL_SCREEN1 >> 16);

current_screen = 0;
}
}

volatile uint16_t *get_screen(void) {
if(current_screen == 0) return fb0;
else return fb1;
}

void vsync(void) {
while(memregs16[0x1182>>1]&(1<<4)); // waiting for V-sync
while(!(memregs16[0x1182>>1]&(1<<4))); // wait for end of vsync
}

void Do940Stuff()
{
// Set up registers
memregs16 = (volatile uint16_t*)mem2addr(0xC0000000);
fb0 = (volatile uint16_t*)mem2addr(PHYSICAL_SCREEN0);
fb1 = (volatile uint16_t*)mem2addr(PHYSICAL_SCREEN1);
screen = fb0;
memregs16[0x28DA>>1] = 0x04AB; // 16bpp, only region 1 activated

memregs16[0x290C>>1] = 640; // in 16bpp mode, this means width = 320

while(1) {
screen = get_screen();
int iy, ix;
for (iy=0; iy<240; iy++) {

for(ix=0; ix<320; ix++) {
screen[iy * 320 + ix] = 0xF800;
}
}
vsync();
flip();
}
}
 

Squidge

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I'm assuming your code is being uploaded to 0x2000000, and your bootstrap is setting the 940 start address properly?
 

Orkie

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Yes, the code is definitely working, I can toggle the backlight etc. I'm using rlyeh's minimal lib to load it:
CODE
#include <stdio.h>
#include "minimal.h"
#include "binsize.h"


int main() {
gp2x_init(1000, 16, 11025,16,1,60, 1);
printf("running code940.bin...\n");
gp2x_dualcore_launch_program_from_disk("code940.bin", 0, SIZE_BIN);
printf("code940.bin has been launched...\n");

while(1) {
}
gp2x_deinit();
return 0;
}

void gp2x_sound_frame(void *blah, void *buff, int samples) {}


Could this be the cause (i.e. is it setting up the hardware in a strange way)?

main.c is just copied straight from the tutorial:
CODE
extern void Do940Stuff();

void code940(void) __attribute__((naked));
void code940(void)
{
asm volatile (
"b .CodeEntryPoint @ have all the entry points jump to start of the code\n"
"b .CodeEntryPoint\n"
"b .CodeEntryPoint\n"
"b .CodeEntryPoint\n"
"b .CodeEntryPoint\n"
"b .CodeEntryPoint\n"
"b .CodeEntryPoint\n"
"b .CodeEntryPoint\n"
".CodeEntryPoint:\n"
"mov sp, #0x100000 @ set the stack top (1M)\n"
"sub sp, sp, #4 @ minus 4, just to be tidy\n"
"@ set up memory region 0 -- the whole 4GB address space, uncached\n"
"@ bit 0 = enable\n"
"@ bits 1-5: 5-bit region size (N). Size = 2^(N+1). For this\n"
"@ partition, set all bits for maximum size\n"
"@ bits 12:31: base address. Both regions in this example have a\n"
"@ base address of zero\n"
"mov r0, #0x3F @ region data\n"
"mcr p15, 0, r0, c6, c0, 0 @ data region 0\n"
"mcr p15, 0, r0, c6, c0, 1 @ code region 0\n"
"@ set up region 1 which is the first 16 megabytes.\n"
"@ bit 0 = enable\n"
"@ bits 1-5: as above. 16 MB is 2^24 so N is 23. In hex, 23==0x17.\n"
"@ (0x17<<1) | 1 = 0x2F\n"
"mov r0, #0x2F @ region data\n"
"mcr p15, 0, r0, c6, c1, 0 @ data region 1\n"
"mcr p15, 0, r0, c6, c1, 1 @ code region 1\n"
"@ set region 1 to be cacheable (so the first 16M will be cacheable)\n"
"mov r0, #2 @ 2 means region 1 (1 would have meant region 0, 4 would mean region 2, etc)\n"
"mcr p15, 0, r0, c2, c0, 0 @ turn on data cache\n"
"mcr p15, 0, r0, c2, c0, 1 @ turn on instruction cache\n"
"@ set region 1 to be bufferable too (only data)\n"
"mcr p15, 0, r0, c3, c0, 0 @ turn on write buffer\n"
"@ set protection on for all regions\n"
"mov r0, #15 @ more than we actually need\n"
"mcr p15, 0, r0, c5, c0, 0 @ set full data permission\n"
"mcr p15, 0, r0, c5, c0, 1 @ set full code permission\n"
"mrc p15, 0, r0, c1, c0, 0 @ fetch current control reg\n"
"orr r0, r0, #1 @ 0x00000001: enable protection unit\n"
"orr r0, r0, #4 @ 0x00000004: enable D cache\n"
"orr r0, r0, #0x1000 @ 0x00001000: enable I cache\n"
"orr r0, r0, #0xC0000000 @ 0xC0000000: async+fastbus\n"
"mcr p15, 0, r0, c1, c0, 0 @ set control reg\n"
// ok, now we're ready to rock
);
Do940Stuff();
}
 

Squidge

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check your minimal lib - rlyeh has used both 0x03000000 and 0x02000000 in his library for the 940 launch address. If it's 0x03000000, then you'll get the exact result you described.
 

skeezix

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If his code is working (toggling backlight etc), then isn't the address irrelevent at that point?

I fiddled and never noticed much diff between 0x02 and 0x03, but I'm not doing much on the 940 beyond pure calculations. *shrug*

jeff
 

Squidge

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I'm just going from what he's posted here, and that code can work at any address by default as gcc generates pretty good PIC unless you have stuff like some 'switch/case' statements. The only problem you'll get is that you'll give the wrong address to the frame buffer pointer registers and then write to a completely different address, causing garbage to be displayed.
 

Orkie

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Well what I've posted is the complete code. I looked through minimal.c and found that it did seem to be using 0x03000000 (CODE
gp2x_dualcore_ram=(unsigned long *)mmap(0, 0x1000000-0x4B000*8-0x4000, PROT_READ|PROT_WRITE, MAP_SHARED, gp2x_dev[2], 0x03000000);
), so I changed it to 0x02000000 and now I get a black screen.

EDIT: I'm using minimal library 0.B preview.
 

Squidge

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isn't 0x02000000 already used in that library? In which case I'd change it back and then change your code to suit, rather than hacking up the library.
 

Orkie

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What do I need to change in my code? It can't be mem2addr, because that works for getting the addresses of other registers :S.
 
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