Let's query a number from the (undocumented) hardware random number generator. You can use this to implement a simple, but accurate dice throw in any game. It is important as without hardware support you can only generate pseudo-random numbers.
#define MMIO_BASE 0x3F000000
#define GPFSEL0 ((volatile unsigned int*)(MMIO_BASE+0x00200000))
#define GPFSEL1 ((volatile unsigned int*)(MMIO_BASE+0x00200004))
#define GPFSEL2 ((volatile unsigned int*)(MMIO_BASE+0x00200008))
#define GPFSEL3 ((volatile unsigned int*)(MMIO_BASE+0x0020000C))
#define GPFSEL4 ((volatile unsigned int*)(MMIO_BASE+0x00200010))
#define GPFSEL5 ((volatile unsigned int*)(MMIO_BASE+0x00200014))
#define GPSET0 ((volatile unsigned int*)(MMIO_BASE+0x0020001C))
#define GPSET1 ((volatile unsigned int*)(MMIO_BASE+0x00200020))
#define GPCLR0 ((volatile unsigned int*)(MMIO_BASE+0x00200028))
#define GPLEV0 ((volatile unsigned int*)(MMIO_BASE+0x00200034))
#define GPLEV1 ((volatile unsigned int*)(MMIO_BASE+0x00200038))
#define GPEDS0 ((volatile unsigned int*)(MMIO_BASE+0x00200040))
#define GPEDS1 ((volatile unsigned int*)(MMIO_BASE+0x00200044))
#define GPHEN0 ((volatile unsigned int*)(MMIO_BASE+0x00200064))
#define GPHEN1 ((volatile unsigned int*)(MMIO_BASE+0x00200068))
#define GPPUD ((volatile unsigned int*)(MMIO_BASE+0x00200094))
#define GPPUDCLK0 ((volatile unsigned int*)(MMIO_BASE+0x00200098))
#define GPPUDCLK1 ((volatile unsigned int*)(MMIO_BASE+0x0020009C))
#include "gpio.h"
/* Auxilary mini UART registers */
#define AUX_ENABLE ((volatile unsigned int*)(MMIO_BASE+0x00215004))
#define AUX_MU_IO ((volatile unsigned int*)(MMIO_BASE+0x00215040))
#define AUX_MU_IER ((volatile unsigned int*)(MMIO_BASE+0x00215044))
#define AUX_MU_IIR ((volatile unsigned int*)(MMIO_BASE+0x00215048))
#define AUX_MU_LCR ((volatile unsigned int*)(MMIO_BASE+0x0021504C))
#define AUX_MU_MCR ((volatile unsigned int*)(MMIO_BASE+0x00215050))
#define AUX_MU_LSR ((volatile unsigned int*)(MMIO_BASE+0x00215054))
#define AUX_MU_MSR ((volatile unsigned int*)(MMIO_BASE+0x00215058))
#define AUX_MU_SCRATCH ((volatile unsigned int*)(MMIO_BASE+0x0021505C))
#define AUX_MU_CNTL ((volatile unsigned int*)(MMIO_BASE+0x00215060))
#define AUX_MU_STAT ((volatile unsigned int*)(MMIO_BASE+0x00215064))
#define AUX_MU_BAUD ((volatile unsigned int*)(MMIO_BASE+0x00215068))
/**
* Set baud rate and characteristics (115200 8N1) and map to GPIO
*/
void uart_init()
{
register unsigned int r;
/* initialize UART */
*AUX_ENABLE |=1; // enable UART1, AUX mini uart
*AUX_MU_CNTL = 0;
*AUX_MU_LCR = 3; // 8 bits
*AUX_MU_MCR = 0;
*AUX_MU_IER = 0;
*AUX_MU_IIR = 0xc6; // disable interrupts
*AUX_MU_BAUD = 270; // 115200 baud
/* map UART1 to GPIO pins */
r=*GPFSEL1;
r&=~((7<<12)|(7<<15)); // gpio14, gpio15
r|=(2<<12)|(2<<15); // alt5
*GPFSEL1 = r;
*GPPUD = 0; // enable pins 14 and 15
r=150; while(r--) { asm volatile("nop"); }
*GPPUDCLK0 = (1<<14)|(1<<15);
r=150; while(r--) { asm volatile("nop"); }
*GPPUDCLK0 = 0; // flush GPIO setup
*AUX_MU_CNTL = 3; // enable Tx, Rx
}
/**
* Send a character
*/
void uart_send(unsigned int c) {
/* wait until we can send */
do{asm volatile("nop");}while(!(*AUX_MU_LSR&0x20));
/* write the character to the buffer */
*AUX_MU_IO=c;
}
/**
* Receive a character
*/
char uart_getc() {
char r;
/* wait until something is in the buffer */
do{asm volatile("nop");}while(!(*AUX_MU_LSR&0x01));
/* read it and return */
r=(char)(*AUX_MU_IO);
/* convert carrige return to newline */
return r=='\r'?'\n':r;
}
/**
* Display a string
*/
void uart_puts(char *s) {
while(*s) {
/* convert newline to carrige return + newline */
if(*s=='\n')
uart_send('\r');
uart_send(*s++);
}
}
/**
* Display a binary value in hexadecimal
*/
void uart_hex(unsigned int d) {
unsigned int n;
int c;
for(c=28;c>=0;c-=4) {
// get highest tetrad
n=(d>>c)&0xF;
// 0-9 => '0'-'9', 10-15 => 'A'-'F'
n+=n>9?0x37:0x30;
uart_send(n);
}
}
void uart_init();
void uart_send(unsigned int c);
char uart_getc();
void uart_puts(char *s);
void uart_hex(unsigned int d);
#include "gpio.h"
/* mailbox message buffer */
volatile unsigned int __attribute__((aligned(16))) mbox[36];
#define VIDEOCORE_MBOX (MMIO_BASE+0x0000B880)
#define MBOX_READ ((volatile unsigned int*)(VIDEOCORE_MBOX+0x0))
#define MBOX_POLL ((volatile unsigned int*)(VIDEOCORE_MBOX+0x10))
#define MBOX_SENDER ((volatile unsigned int*)(VIDEOCORE_MBOX+0x14))
#define MBOX_STATUS ((volatile unsigned int*)(VIDEOCORE_MBOX+0x18))
#define MBOX_CONFIG ((volatile unsigned int*)(VIDEOCORE_MBOX+0x1C))
#define MBOX_WRITE ((volatile unsigned int*)(VIDEOCORE_MBOX+0x20))
#define MBOX_RESPONSE 0x80000000
#define MBOX_FULL 0x80000000
#define MBOX_EMPTY 0x40000000
/**
* Make a mailbox call. Returns 0 on failure, non-zero on success
*/
int mbox_call(unsigned char ch)
{
unsigned int r = (((unsigned int)((unsigned long)&mbox)&~0xF) | (ch&0xF));
/* wait until we can write to the mailbox */
do{asm volatile("nop");}while(*MBOX_STATUS & MBOX_FULL);
/* write the address of our message to the mailbox with channel identifier */
*MBOX_WRITE = r;
/* now wait for the response */
while(1) {
/* is there a response? */
do{asm volatile("nop");}while(*MBOX_STATUS & MBOX_EMPTY);
/* is it a response to our message? */
if(r == *MBOX_READ)
/* is it a valid successful response? */
return mbox[1]==MBOX_RESPONSE;
}
return 0;
}
/* a properly aligned buffer */
extern volatile unsigned int mbox[36];
#define MBOX_REQUEST 0
/* channels */
#define MBOX_CH_POWER 0
#define MBOX_CH_FB 1
#define MBOX_CH_VUART 2
#define MBOX_CH_VCHIQ 3
#define MBOX_CH_LEDS 4
#define MBOX_CH_BTNS 5
#define MBOX_CH_TOUCH 6
#define MBOX_CH_COUNT 7
#define MBOX_CH_PROP 8
/* tags */
#define MBOX_TAG_GETSERIAL 0x10004
#define MBOX_TAG_LAST 0
int mbox_call(unsigned char ch);
rand_init()
initializes the hardware.
rand(min,max)
returns a random number between min and max.
https://www.raspberrypi.org/forums/viewtopic.php?t=196015
https://github.com/raspberrypi/linux/blob/204050d0eafb565b68abf512710036c10ef1bd23/drivers/char/hw_random/bcm2835-rng.c
#include "gpio.h"
#define RNG_CTRL ((volatile unsigned int*)(MMIO_BASE+0x00104000))
#define RNG_STATUS ((volatile unsigned int*)(MMIO_BASE+0x00104004))
#define RNG_DATA ((volatile unsigned int*)(MMIO_BASE+0x00104008))
#define RNG_INT_MASK ((volatile unsigned int*)(MMIO_BASE+0x00104010))
/**
* Initialize the RNG
*/
void rand_init()
{
*RNG_STATUS=0x40000;
// mask interrupt
*RNG_INT_MASK|=1;
// enable
*RNG_CTRL|=1;
}
/**
* Return a random number between [min..max]
*/
unsigned int rand(unsigned int min, unsigned int max)
{
// may need to wait for entropy: bits 24-31 store how many words are
// available for reading; require at least one
while(!((*RNG_STATUS)>>24)) asm volatile("nop");
return *RNG_DATA % (max-min) + min;
}
void rand_init();
unsigned int rand(unsigned int min, unsigned int max);
#include "uart.h"
#include "mbox.h"
#include "rand.h"
void main()
{
// set up serial console
uart_init();
// set up random number generator
rand_init();
uart_puts("Here goes a random number: ");
uart_hex(rand(0,4294967295));
uart_puts("\n");
// get the board's unique serial number with a mailbox call
mbox[0] = 8*4; // length of the message
mbox[1] = MBOX_REQUEST; // this is a request message
mbox[2] = MBOX_TAG_GETSERIAL; // get serial number command
mbox[3] = 8; // buffer size
mbox[4] = 8;
mbox[5] = 0; // clear output buffer
mbox[6] = 0;
mbox[7] = MBOX_TAG_LAST;
// send the message to the GPU and receive answer
if (mbox_call(MBOX_CH_PROP)) {
uart_puts("My serial number is: ");
uart_hex(mbox[6]);
uart_hex(mbox[5]);
uart_puts("\n");
} else {
uart_puts("Unable to query serial!\n");
}
// echo everything back
while(1) {
uart_send(uart_getc());
}
}
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Project Source Code: Bare-Metal-Mini-PiOS
Author : andykuo8766
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