My BBC Acorn model B is working again. The original monitor is still dead.
Time to play with some machine code and ROMs.
My machine has a NFS rom installed. (NetFS)
Econet was Acorn Computers’s low-cost local area network system, intended for use by schools and small businesses. It was widely used in those areas, and was supported by a large number of different computer and server systems produced both by Acorn and by other companies.
I found a ROM online called Gremlin. It is a 16K rom file. But at the moment I only got some 28C64 (8k) or 28C256 (32k) eeproms.
32k it is. But de beeb having address line A14 floating high, I need to flash the upper 16k of the 32k ROM.
Ben posted a youtube about Wozmon running on his 6502.
In 1976, Steve Wozniac wrote what’s commonly known simply as Wozmon.
Wozmon is a machine-code monitor program written by Wozniak for the Apple 1. In Only 256 bytes ! Being pure 6502 code easily adaptable. A monitor program allows you to view/edit and run machine code using simple commands.
I’ve got a different setup as Ben’s computer. But changing the necessary, and it will run on my 6502.
I’m not using rs232 voltage levels (-7 till -25 and +7 till +25 volts). I’m using a usb serial uart standard 5v leveling stick …
For address decoder see other post
Simplified schematic of my UART/ACIA
Compiling the Wosmon gave me an error, DEC is not a valid opcode for a bare 6502 .. but we have a 65c02. Solution: Add -c02 extra opcodes
error 1 in line 187 of "wozmon.s": illegal operand types
> DEC ; Decrement A.
# fix .. add -c02
vasm6502_oldstyle -c02 -Fbin -dotdir wozmon.s
Below Apple I Manual with the sourcecode for Wozmon
Uploading didn’t work Solution: Using chrome it had access to the usb port to upload, firefox didn’t work
The program didn’t compile, faulty or zero size hex file. Solution: Wrong Maqueen library was in the examples (After changing, needed version update also, see below)
Not everything is in Dutch (I like English, but this is for the boy), maqueen V2 needed a lot of translation. (So we joined https://crowdin.com/project/makecode/nl to help translating the libraries)
Apparently my AI camera can be connected to this robot!
I wrote a little python script which checks the checksum of a Bios.
In a previous post i used hexedit to play around changing a Bios dump.
Below posted python script calculates the checkum using the following:
Add all bytes in the file and do a modulo 256 on this number. The output should be 0.
My previous edit gave me a output of C2, so I changed an unused byte FF into (FF-C2) 3D. No more checksum errors when booting!
Next to do, get a Bios like Glabios or PcXtBios to start my own code from a secondary Eeprom.
import sys
# Bios sum modulo should be 0
# edit last or unused byte to fix
# python bios-checksum-test.py MYROM.edit.checksum
# 0
f = open(sys.argv[1],'rb')
m = f.read()
print '%x' % ( ( sum(ord(c) for c in m) & 0xFFFFFFFF ) % 256 )
Python3
import sys
# Bios sum modulo should be 0
# edit last or unused byte to fix
# python bios-checksum-test.py MYROM.edit.checksum
# 0
f = open(sys.argv[1],'rb')
m = f.read()
checksum = ( ( sum((c) for c in m) & 0xFFFFFFFF ) % 256 )
print(checksum, 'in hex =', hex(checksum))
PlatformIO tested ( install StackArray.h in lib/StackArray/StackArray.h )
Reset button and dipswitches for below options
Visited pathmode ( dip switch 1)
Preview maze generation ( dip switch 3)
Hard mode – starts at first position when hitting a wall ( dip 2 )
Longest path mode (longest stackarray before stack.pop (dip 4 )
Prints serial info, like a drawn maze
Pixel remapping for other displays ( Below mapping i had to use, see source sketch )
How is the maze generated?
It is generated using recursive backtracking:
Start at 0,0 mark visited, select a random direction from unvisited neighbours, push current on the stack, goto new location, and mark this visited. Repeat until no possible directions. pop from the stack a previous location, another direction possible? Take that path and repeat. Repeat popping from stack, until stack empty .. now all cells are visited
Make an initial cell the current cell
mark it as visited
While there are unvisited cells
If the current cell has any neighbours
which have not been visited
Choose randomly one of the unvisited neighbours
Push the current cell to the stack
Mark wall hole
Make the chosen cell the current cell
mark it as visited
Else if stack is not empty
Pop a cell from the stack
Make it the current cell
This is my implementation of backtracking
The displaymatrix function is a implementation of different led mappings
Still have to decide where to place endpoint … At 8,8 or at first stack pop? Maybe both?
Code
#include <WEMOS_Matrix_LED.h>
#include <StackArray.h>
int directions[4]{};
int notalldone = 1;
int tmpx=0;
int tmpy=0;
int x = 1;
int y = 1;
MLED mled(5); //set intensity=5
int maze[8][8] = {
};
int displaymatrix[8][8] = {
{ 0,1,2,3,4,5,6,7 },
{ 8,9,10,11,12,13,14,15 },
{16,17,18,19,20,21,22,23},
{24,25,26,27,28,29,30,31},
{32,33,34,35,36,37,38,39},
{40,41,42,43,44,45,46,47},
{48,49,50,51,52,53,54,55},
{56,57,58,59,60,61,62,63}
};
int visitmatrix[10][10] = {
1,1,1,1,1,1,1,1,1,1,
1,0,0,0,0,0,0,0,0,1,
1,0,0,0,0,0,0,0,0,1,
1,0,0,0,0,0,0,0,0,1,
1,0,0,0,0,0,0,0,0,1,
1,0,0,0,0,0,0,0,0,1,
1,0,0,0,0,0,0,0,0,1,
1,0,0,0,0,0,0,0,0,1,
1,0,0,0,0,0,0,0,0,1,
1,1,1,1,1,1,1,1,1,1
};
void setup() {
Serial.begin(115200);
randomSeed(analogRead(0));
mazegen();
drawmaze();
}
void mazegen(){
visitmatrix[x][y]=1;
StackArray <int> rowStack;
StackArray <int> colStack;
rowStack.push(x);
colStack.push(y);
while(notalldone == 1){
visitmatrix[x][y]=1;
while(!rowStack.isEmpty()) {
int count=0;
//up
if ( visitmatrix[x-1][y] == 0 ){
directions[count]=1;
count++;
}
//right
if ( visitmatrix[x][y+1] == 0 ){
directions[count]=2;
count++;
}
//down
if ( visitmatrix[x+1][y] == 0 ){
directions[count]=4;
count++;
}
//left
if ( visitmatrix[x][y-1] == 0 ){
directions[count]=8;
count++;
}
// no dir found
if (count == 0 ) {
mled.dot(x-1,y-1);
mled.display();
x = rowStack.pop();
y = colStack.pop();
Serial.println("popping ");
} else {
// count random direction
int dir = directions[random(count)];
Serial.println("push ");
rowStack.push(x);
colStack.push(y);
Serial.print("nr dir : ");
Serial.println(count);
//delay(100);
Serial.println(dir);
// move 1,1 to 0,0
mled.dot(x-1,y-1);
mled.display();
// set direction in maze, dit moet bit set worden
int mybits = maze[x-1][y-1];
int storedir = mybits | dir;
maze[x-1][y-1] = storedir;
if ( dir == 1){
int getup = maze[x-2][y-1];
int storedir = getup | 4;
maze[x-2][y-1] = storedir;
}
if ( dir == 2){
int getup = maze[x-1][y];
int storedir = getup | 8;
maze[x-1][y] = storedir;
}
if ( dir == 4){
int getup = maze[x][y-1];
int storedir = getup | 1;
maze[x][y-1] = storedir;
}
if ( dir == 8){
int getup = maze[x-1][y-2];
int storedir = getup | 2;
maze[x-1][y-2] = storedir;
}
// maze[x-1][y-1] = dir;
//set new square
if (dir == 1){ x--; }
if (dir == 2){ y++; }
if (dir == 4){ x++; }
if (dir == 8){ y--; }
visitmatrix[x][y]=1;
drawmaze();
}
}
notalldone = 0; //#2
// if found 0 in 10x10 matrix visited, do
for(int checkx=0;checkx<10;checkx++){
for(int checky=0;checky<10;checky++){
if ( visitmatrix[checkx][checky] == 0 ){
tmpx=x;
tmpy=y;
notalldone = 1;
}
}
}
}
rowStack.push(tmpx);
colStack.push(tmpy);
}
void drawmaze(){
Serial.println("Generating done - Drawing");
for(int ledx=0;ledx<8;ledx++)
{
for(int ledy=0;ledy<8;ledy++){
Serial.print(maze[ledx][ledy]);
if ( maze[ledx][ledy] != 0 ) {
mled.dot(ledx,ledy); // draw dot
mled.display();
// delay(50);
}
}
Serial.println("");
}
Serial.println("");
delay(100);
}
void loop() {
}
"If something is worth doing, it's worth overdoing."
