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
Using searle’s design, i can draw pixels using composite video out.
Converting b/w png to hex include files, for usage in vasm I did the following.
#Python script to convert black levels to pixels
from PIL import Image
i = Image.open("fash.png")
pixels = i.load() # this is not a list, nor is it list()'able
width, height = i.size
all_pixels = []
for x in range(width):
for y in range(height):
cpixel = pixels[x, y]
if cpixel[1] == 255:
s = '\t.db 0x05,' + hex(int(x)) + ',' + hex(int(y))
print (s)
Running and output example
python3 image.py > out
head out
.db 0x05,0x1,0x16
.db 0x05,0x1,0x18
.db 0x05,0x1,0x19
.db 0x05,0x2,0x7
.db 0x05,0x2,0x8
.db 0x05,0x2,0xc
.db 0x05,0x2,0xd
.db 0x05,0x2,0x17
.db 0x05,0x3,0x5
Control codes and vasm include
01 (01) - Cursor home (Standard ASCII)
04 (04) - Cursor solid
05 (05) - Set graphics pixel (next two bytes = x,y)
0C (12) - Clear screen (Standard ASCII)
0D (13) - Carriage return (Standard ASCII)
0E (14) - Set column 0 to 79 (2nd byte is the column number) or 0 to 39 for a 40 char line
0F (16) - Set row 0 to 24 (2nd byte is the row number)
1B (27) - ESC - reserved for ANSI sequences
vasm include part:
message:
.db 0x01,0x0c ; home and clear
.db 0x1b,0x2d ; disable ansi translation
include "out" ; include hex "png"
.db 0x00 ; end with 0 (part of message print routine)
I’ve got a ROM in my 6502 which can load programs at $0200. When running own programs i want to use IRQ’s, but my rom is also using IRQ routines. So i was wondering if i could ‘hijack’ this IRQ for own program purposes.
So i’ve altered the rom to use a vector in userspace.
CPU starts, getting vector from FFFC
Goto $8000 main ROM program
Setting a jmp routine on zero page $F0
4C C9 FF
4C C9 FF ; second time, first one will redirect
Running my program on $0200
Change first jmp C9 FF to my own IRQ part
Changed jmp vectors
4C 6E 02 ; jmp $026E (myprg)
4C C9 FF ; jmp $FFC9 (rom)
Run rest of program
All seems fine and dandy … buzzer is sounding, but no blinky leds. When flashing the rom with only my program, everything works .. So whats going on? .. anyone?
MYIRQ = $F0 ; Own IRQ vector <=================== my additions/alterations
; Below definitions for VIA 1 my loadable program uses VIA 2
PORTB = $6000 ; VIA port B
PORTA = $6001 ; VIA port A
DDRB = $6002 ; Data Direction Register B
DDRA = $6003 ; Data Direction Register A
-------------8<------- snip
PROGRAM_LOCATION = $0200 ; memory location for user programs
.org $8000
main: ; boot routine, first thing loaded
ldx #$ff ; initialize the stackpointer with 0xff
txs
; ISR redirect code <=================== my additions/alterations
sei
lda #$4C
sta MYIRQ
sta MYIRQ + 3
lda #<ISR
sta MYIRQ + 1
sta MYIRQ + 4
lda #>ISR
sta MYIRQ + 2
sta MYIRQ + 5
cli
; End ISR redirect <=================== till here
; below this the standard rom routines
-------------8<------- snip
.org $FFC9 ; as close as possible to the ROM's end
ISR: <====================== Whole ISR not my code
CURRENT_RAM_ADDRESS = Z0 ; a RAM address handle for indirect writing
pha
tya
pha
lda ISR_FIRST_RUN ; check whether we are called for the first time
bne .write_data ; if not, just continue writing
lda #1 ; otherwise set the first time marker
sta ISR_FIRST_RUN ; and return from the interrupt
jmp .doneisr
.write_data:
lda #$01 ; progressing state of loading operation
sta LOADING_STATE ; so program_ram routine knows, data's still flowing
lda PORTB ; load serial data byte
ldy #0
sta (CURRENT_RAM_ADDRESS),Y ; store byte at current RAM location
; increase the 16bit RAM location
inc CURRENT_RAM_ADDRESS_L
bne .doneisr
inc CURRENT_RAM_ADDRESS_H
.doneisr
pla ; restore Y
tay
pla ; restore A
rti
.org $fffc
.word main ; Main ROM program
.word MYIRQ ; Redirect to OWN irq vector <=================== my additions/alterations
RAM Program
; Second VIA stuff
PORTB = $5000
PORTA = $5001
DDRB = $5002
DDRA = $5003
;------------------8<-------------
; Vector pointer on zero page
MYIRQ = $F0
ticks = $00 ; 4 Bytes
toggle_time = $04 ; 1 Byte
.org $0200
start:
; IRQ REDIRECT
sei ; irq masked
lda #<irq ; get low byte IRQ routine address
sta MYIRQ + 1 ; store at $F1
lda #>irq ; get high part of address
sta MYIRQ + 2 ; store at $F2
cli ; irq enabled
; IRQ END REDIRECT
; init of program part
lda #%11111111
sta DDRA
sta DDRB
lda #$00
sta PORTA
sta PORTB
sta toggle_time
jsr init_timer
lda #$77
sta T1CL
lda #$07
sta T1CH
loop: ; loop
jsr update_led ; update led routine
jmp loop
update_led:
sec
lda ticks
sbc toggle_time
cmp #25
bcc exit_update_led
; Toggle led
lda #%01000000
eor PORTB
sta PORTB
lda ticks
sta toggle_time
exit_update_led:
rts
;-----------------------------8<------------- snip
irq:
pha
lda #$0e
sta T2CL
lda #$27
sta T2CH
inc ticks
bne end_irq
inc ticks + 1
bne end_irq
inc ticks + 2
bne end_irq
inc ticks + 3
end_irq:
pla
jmp MYIRQ + 3 ; jmp to vector which points to ROM routine ; should be $FFC9
Buzzer and led on VIA 2, blinky and sound timed by the internal timers of the 6522
ACIA testing still going on, writing software
Mini matrix keyboard removed, and used the temporary cursor buttons for the test with a rom which allows for a 8bits upload method using a arduino and the 6522. (I’m working on the big keyboard)
Work in progress code
PORT2B = $5000 ; VIA PORTB
PORT2A = $5001 ; VIA PORTA
DDR2B = $5002 ; Data direction register
DDR2A = $5003 ; Data direction register
PORTB = $6000 ; display
PORTA = $6001 ; control display + matrix keyboard
DDRB = $6002 ; data direction register
DDRA = $6003 ; data direction register
SID = $7000 ; sid base address
E = %10000000 ; enable bit
RW = %01000000 ; RW bit
RS = %00100000 ; Register Select bit
HOME = %00000010 ; VIA PORTB HOME command
DADDR = %00010000 ; VIA DADDRESS
LINENO = $0200 ; temp address linenumber (move to other location)
NEXTLINE = 40 ; 2x16 Chars but internally 40
.org $8000
reset:
ldx #$ff
txs ; reset stack
; ###################################################
; # DISPLAY CONTROL #
; ###################################################
; VIA Setup
lda #%11111111 ; Set all pins on port B to output
sta DDRB
lda #%11100000 ; Set top 3 pins on port A to output
sta DDRA
; DISPLAY Setup
lda #%00111000 ; Set 8-bit mode; 2-line display; 5x8 font
jsr lcd_instruction
lda #%00001110 ; Display on; cursor on; blink off
jsr lcd_instruction
lda #%00000110 ; Increment and shift cursor; don't shift display
jsr lcd_instruction
lda #$00000001 ; Clear display
jsr lcd_instruction
; ###################################################
; # PRINT MESSAGE LINE NO 0 #
; ###################################################
lda #0 ; set line number
sta LINENO ; store for subroutine
jsr gotoline ; move cursor
ldx #0 ; message index pointer
print:
lda message0,x ; start of message
beq nextprint ; stop when null in message (asciiz <- Zero padded)
jsr print_char ; print char
inx ; incr index
jmp print ; resume print
; ###################################################
; # PRINT MESSAGE LINE NO 1 #
; ###################################################
nextprint:
lda #1 ; set line number
sta LINENO ; store
jsr gotoline
ldx #0 ; index pointer
print2:
lda message1,x ; absolute address message + x in A
beq sidsound ; if x is 0, end of message
jsr print_char ; jump subroutine
inx ; increment x
jmp print2 ; loop print2
; ###################################################
; # SID SOUND #
; ###################################################
sidsound:
lda #0
sta SID+$5 ; attack/decay duration
lda #250
sta SID+$6 ; sustain level/release duration
lda #$95 ; frequency voice 1 low byte
sta SID+$0
lda #$44 ; frequency voice 1 high byte
sta SID+$1
lda #%00100001 ; sawtooth + gate
sta SID+$4 ; control register voice 1
lda #$0f ; filter mode and volume (bits 3-0 main volume)
sta SID+$18 ; filter mode and volume
; ###################################################
; # 2ND VIA #
; ###################################################
lda #%11111111 ; set port A output
sta DDR2A
lda #%11111111 ; all ones!
sta PORT2A
; ###################################################
lda #%11111111 ; set port A output
sta DDR2A
lda #%11111111 ; all ones!
sta PORT2A
; ###################################################
; # MAIN PROGRAM LOOP #
; ###################################################
loop:
jmp loop
; 1234567812345678
message0: .asciiz "VIA 1,2 SID TEST"
message1: .asciiz " FASH 2022 "
; ###################################################
; # ONLY SUBROUTINES #
; ###################################################
; ###################################################
; # Subroutine gotoline #
; # Moves character placement position on display #
; # Needs : $LINENO ADDRESS #
; # Exit values : - #
; # Destroys registers: - #
; ###################################################
gotoline:
pha ; store a
txa
pha ; store x
ldx LINENO
lda #HOME ; cursor down
jsr lcd_instruction
lda #$80
nextline:
ldx LINENO
cpx #00
beq endnextlines
loopline:
adc #40
jsr lcd_instruction
dex
stx LINENO
jmp nextline
endnextlines:
pla ; pop a
tax ; a to x
pla ; pop a
rts
; ###################################################
; # LCD SUBROUTINES #
; ###################################################
lcd_wait:
pha
lda #%00000000 ; Port B is input
sta DDRB
lcdbusy:
lda #RW
sta PORTA
lda #(RW | E)
sta PORTA
lda PORTB
and #%10000000
bne lcdbusy
lda #RW
sta PORTA
lda #%11111111 ; Port B is output
sta DDRB
pla
rts
lcd_instruction:
jsr lcd_wait
sta PORTB
lda #0 ; Clear RS/RW/E bits
sta PORTA
lda #E ; Set E bit to send instruction
sta PORTA
lda #0 ; Clear RS/RW/E bits
sta PORTA
rts
print_char:
jsr lcd_wait
sta PORTB
lda #RS ; Set RS; Clear RW/E bits
sta PORTA
lda #(RS | E) ; Set E bit to send instruction
sta PORTA
lda #RS ; Clear E bits
sta PORTA
rts
nmi:
rti
irq:
rti
.org $fffa
.word nmi
.word reset
.word irq
; .word $0000
Above is my design for a hex keyboard to enter opcodes in hex using a simple monitor program. i used a 74ls922 which can decode a 4×4 matrix. I’d rather had a 74ls723 which can encode 20 keys.
Nowhere to be found. So i have to think of a new plan.
Now it is configured as follows:
C
D
E
F
8
9
A
B
4
5
6
7
0
1
2
3
When pressing the alternate key
addr (to implement)
run (1/2 implemented)
reset (to implement)
step instruction (to implement)
memory next
memory previous
PCB design for matrix hexboard with place for notes
Meanwhile i’ve ordered new keys (the ones i’ve been using for my photomanager project and wnat to have a setup like this:
?
?
addr
run
reset
C
D
E
F
?
8
9
A
B
step
4
5
6
7
mem next
0
1
2
3
mem prev
When you want to show the status of busses and alike, you can’t use a led and restistor directly on the bus, it will require too much current. So i’ve been using below schematic which uses a darlington array.
Now i can display databus, address bus and i’ve been using this for address decoding logic and hex keyboard.
I’ve implemented a second VIA chip, and ordered components to amplify the SID sound part
The workshop at MCH2022 gave me the idea to make my next PCB not at home, but professionally.
I’m planning to make my 6502 on modular PCB’s when i’ve got the base part working. ( I probably will only make THT (Though Hole Technology) boards instead of smd ) So i’ll probably end up making a few boards, namely:
Power on reset
Clock module
Interconnect with arduino
CPU, memory and ROM
Display
6522 Via
SID chip
Hex keyboard
This power-on reset is based on the original C64 part to reset the CPU when you power the machine on. With my 6502 i have to manually push reset to start booting. (The CPU starts in a unknown state when you power it up, it needs a reset)
MCH2022 is a nonprofit outdoor hacker camp taking place in Zeewolde, the Netherlands, July 22 to 26 2022. The event is organized for and by volunteers from the worldwide hacker community.
Knowledge sharing, technological advancement, experimentation, connecting with your hacker peers and hacking are some of the core values of this event.
MCH2022 is the successor of a string of similar events happening every four years since 1989. These are GHP, HEU, HIP, HAL, WTH, HAR, OHM and SHA.
I’ve bin to several of these big events. Besides these big events are many different smaller events (wannull, ne2000 etc).
First one i’ve been was HIP97. I went with Bigred at that time. I had to get the tickets at that time, he didn’t had a handle at that time. It was Monique who came up with his new nick.
After HIP97 there was HAL2001 WTH2005 and OHM2013 which i was present. HAL2001 the whole ICEcrew was present, WTH a part of them, OHM a few and i was with a few PRUTS friends.
Now i was with my girlfriend, AND with Bigred again! Loads of fun and memories. Had not seen Bigred since a inbetween hacker party at my place. So ’97 and now ’22 .. jeez 25 years!
So MCH, it was great again. Loads of stuff to do and to see. Weather was … okay. Two days where really hot, one day some light rain but a load of wind. Our neighbours tent collapsed, beer tents where reenforced. First campsite with a supermarket! Music stage was awesome, lasers and fire!
I went to a lot of talks, even my girlfriend found some she was interested in.
OpeningAt nightLast time my tapeTinkeringtar cz ourstuff.tgz
This was the last time i’ve brought my “Windows free zone tape” This big roll of tape was used on many occasions. I got this roll somewhere < 2000, I did a search but couldn’t find anything mentioning it on the web. Maybe some archive.org entry?
Starting a Home Computer Museum (which i almost did in the past)
streaming 360 video (going to try this with my Vuze XR Camera)
Non-Euclidean Doom: what happens to a game when pi is not 3.14159… (Really enjoyed this one)
Hacking the genome: how does it work, and should we?
And more
Besides the talks i’ve done some workshops:
Micropython on the badge (see my other post)
Kicad – PCB designing
Meanwhile we where looking at all the villages and hackerspaces. Loads of interesting people to meet. Like our neighbour two tents futher, he was also a home-brewer, and he brought a minifridge with beer taps connected to it.
When back at our tent or Bigreds Campervan, we talked about differences now and then. New technology, what we’ve been upto in the last years and tinkering, loads of tinkering.
I’ve brough a big plastic container with .. ehh “things to do ….”
My 6502, bigred helped me debugging the 16*2 display. (Luckily his campervan was packed with electronics!) We cannibalized one of his projects for a display, and re-flashed his eeprom programming arduino to test my display. ( The arduino i had to reflash later to program a rom he had given me for my 6502. ) Other toys he gave me: Print for the programmer, and a C64 Cartridge print for Exrom and Game.
Mini C64 with a little screen and raspberry zero.
5050 ledstrip (didn’t had time to reprogram this for our mood-light)
Handheld gamehat: Bigred found some old games he played when he was young
Mikrotik router, because i wanted to make a dmz for my girlfriends laptop. (MS)
Playing around with my Vuze XR camera
Huskycam, which i’m planning to use on a racetrack
DVB-T DAB FM Stick, got some hints and tips from Bigred. (Note to myself … fix the antenna!)
My Arduino touch bagpipe player with i2c
The wifi deauther, which has a display which i wanted to use to make a programmable clock for my 6502. Using a rotary encoder and the display to control the speed in Hz.
I spend many hours playing with the Badge and Kicad
Wrote some 6502 assembly, arduino sketches, php, bash and micropython.
While playing around with the badge i got some things working easily. Spinning logo and blinky leds. Next goal to achieve was, to get the gyroscope to control the angle of spinning. Most of the code worked, but the gyro values stayed zero! (After many hours …. you have to start/enable the chip/measurements on the bno055 first! .. duh! )
I didn’t had my dev directory from my main battlestation synced in my nextcloud, so changing things for the 6502 was a b*tch. Used vasm and acme to generate a bin file to use to fill the rom. Didn’t like the eeprom programmer program, because i could not easily check the rom contents. Have to look into that later on.
While learning to use Kicad, which i only had been using to draw schematics (besides fritzing) , i learned to create a pcb. Which gave me the idea to make a print for the power-on-reset for the 6502. Which is going to be the first PCB by ordering, instead of the old skool messing around with DIY print making. (see next post)
….. Oh, why my display was not working? I even connected my 8bit logic analyzer to the pins of the display.
Everything was correct. But i didn’t use a variable resistor for the contrast. Just a simple resistor i could find. Luckily … bigreds stash. All those hours debugging, all for one resistor! (I have to mention, we had a suspicion halfway. But it was too hot and we where too lazy to go to Bigred’s campervan, to get a potentiometer. )
65c22 connected, new data, and address-bus ribboncables!
First led on Register B blinking!
Notes: Temporary display wil be 2×16 Chars. Ram in place, but not connected (is emulated by the Arduino Mega at the moment) Rom is somewhere halfway the atlantic ocean .. still waiting on that one. Ben Eatons clock module is disconnected, i’m using the Arduino as programmable clock right now. (There wil be a little display and a rotary encoder to set clock speed.)
lda #$ff ; all bits
sta $6002 ; set direction (out) for B register
lda #$80 ; set 1 bit
sta $6000 ; set register B
lda #$00 ; reset bit
sta $6000 ; set register B
jmp $8005 ; jmp to bit set part
"If something is worth doing, it's worth overdoing."
