Contributor: Rick Bronson

The R36S is a very powerful little handheld computer, that comes with the Ubuntu Linux based ArkOS Open Source operating system preinstalled. The system is built with emulation in mind, but as it is a standard Linux based system, it is quite straightforward to write native programs and games for it.

The hardware make up of the R36S is:

- Rockchip RK3326 Quad-core ARM Cortex-A35 CPU with GPU

- One Gigabyte Micron DDR RAM

- RK817 PMIC with RTC and CODEC

- TCS7191A Class-D audio power amplifier

- ME4057 Lithium Ion Battery Linear Charger

- 3.5-inch LCD panel (640 x 480) is Sitronix ST7703 or Elida KD35T133 or clone of

- One or two SD Card slots, headphone output, one charging USB-C, one USB-C OTG

Here is a photo of the main PCB:


1. Connect Wifi dongle to the right hand USB-C port. Not all WiFi dongles work, especially newer ones. Your best bet is Realtek or Ralink, the units that come with an internal WiFi module use a RTL8188.

To fix this we can exit emulator system by Menu→Quit→Quit Emulationstation. This will turn the EmulationStation off, until next time you reboot the R36S. If you want to permanently disable ES, then do:

You can always bring it back by doing:

This example is a simple C++ program to put fonts using standard installable fonts on the screen:

We get some TTF fonts on the screen:


alsamixer # set volume, ESC to exit

aplay /usr/share/sounds/alsa/Rear_Right.wav

cd ~/git/r36s-programming/cprog/devmem

make

sudo ./devmem2 0xff040000; sudo ./devmem2 0xff250000; sudo ./devmem2 0xff260000; sudo ./devmem2 0xff270000

You can also turn on/off the green led (GPIO2 PB5 = 77) via:

pin=77

echo 0 > /sys/class/gpio/gpio$pin/value

echo 1 > /sys/class/gpio/gpio$pin/value

CFLAGS=-c -Wall -O2

LIBS = -lm

PROG = devmem2

INCLUDES = -I. -I/usr/include

devmem2: devmem2.c

gcc devmem2.c -o devmem2

clean:

rm -rf *o $(PROG)

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <string.h>

#include <errno.h>

#include <signal.h>

#include <fcntl.h>

#include <ctype.h>

#include <termios.h>

#include <sys/types.h>

#include <sys/mman.h>

#define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \

__LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0)

#define MAP_SIZE 4096UL

#define MAP_MASK (MAP_SIZE - 1)

int main(int argc, char **argv) {

int fd;

void *map_base, *virt_addr;

unsigned int read_result, writeval;

off_t target;

int access_type = 'w';

if(argc < 2) {

fprintf(stderr, "\nUsage:\t%s { address } [ type [ data ] ]\n"

"\taddress : memory address to act upon\n"

"\ttype : access operation type : [b]yte, [h]alfword, [w]ord\n"

"\tdata : data to be written\n\n",

argv[0]);

exit(1);

}

target = strtoul(argv[1], 0, 0);

if(argc > 2)

access_type = tolower(argv[2][0]);

if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;

fflush(stdout);

/* Map one page */

map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~MAP_MASK);

if(map_base == (void *) -1) FATAL;

fflush(stdout);

virt_addr = map_base + (target & MAP_MASK);

switch(access_type) {

case 'b':

read_result = *((unsigned char *) virt_addr);

break;

case 'h':

read_result = *((unsigned short *) virt_addr);

break;

case 'w':

read_result = *((unsigned long *) virt_addr);

break;

default:

fprintf(stderr, "Illegal data type '%c'.\n", access_type);

exit(2);

}

printf("Value at address 0x%X (%p): 0x%X\n", (int) target, virt_addr, (int) read_result);

fflush(stdout);

if(argc > 3) {

writeval = strtoul(argv[3], 0, 0);

switch(access_type) {

case 'b':

*((unsigned char *) virt_addr) = writeval;

read_result = *((unsigned char *) virt_addr);

break;

case 'h':

*((unsigned short *) virt_addr) = writeval;

read_result = *((unsigned short *) virt_addr);

break;

case 'w':

*((unsigned long *) virt_addr) = writeval;

read_result = *((unsigned long *) virt_addr);

break;

}

printf("Written 0x%X; readback 0x%X\n", writeval, read_result);

fflush(stdout);

}

if(munmap(map_base, MAP_SIZE) == -1) FATAL;

close(fd);

return 0;

}