I porting an Applesoft on 6502

----------------------------------------------

Configuration:
==============
Debug:      0
LCD-DISP:   0
SPI-RAM:    0 Bytes
SRAM Size:  6144 Bytes
SRAM_START: 0x0
SRAM_END:   0x17FF

\
6000R

6000: 4C

]10 A=1

]20 A=A+2

]30 FOR I = 3 TO INT(A/2) STEP 2

]40 IF A/I=INT(A/I) THEN 70

]50 NEXT

]60 PRINT A;" ";

]70 GOTO 20

]RUN
5 7 11 13 17 19 23 29

Progress update for August:

- I was able to get RetroShield 6502 running full speed (1.0 MHz) using Teensy 3.5 board.  Teensy3.5 has 120MHz ARM Cortex-M4 processor, 256KB RAM, SD Card, and 5.0V tolerant. I will build a nice adapter board for us.

- Finishing 1802 took way longer than I planned but finally completed. It felt like a Star Trek episode since I had to go uncharted territories. However I cleaned up the designs and released the final sch, pcb,sw for 1802,8031, and 8085 on the GitLab repo.

- I attended Vintage Computer Festival West and demo'ed RetroShields. Lots of interest.  Highlight for me was we got Monster6502 CPU running on RetroShield, making RetroShield the 3rd hardware platform Monster6502 is tested on :)  We had to slow the system clock to 40kHz but it worked. https://www.monster6502.com/

- Michael Steil and I brought up Commodore 64 Basic running on RetroShield6502. We are basically mapping the screen memory onto VT100 terminal.  It does have blue background and cursor keys are fully emulated, meaning you can move up/down/left/right and edit lines. Michael is the man when it comes to c64.

- While bringin up C64, we also brought up NGT30 VGA+Keyboard Shield.  It worked right away and I can say simple to use.

- I created a mailing list for RetroShields.  If anybody is interested in joining, you can do so at https://groups.io/g/retroshield

- The next batch of processors are Signetics 2650, Motorola 6803 and Intel 8080.

- I also got chips for 4004, 4040, 8008, and lot more, so we should have pretty much the whole cpu line-up soon (well, expect 2months per a batch of 3 so it will take awhile).

I'm pretty excited about Teensy. This should make 1802 and 8085 more enjoyable. 1802 takes 8 clock cycles for each cpu cycle, plus UART is bit-banged (each baud is 300 clock cycles), so UI is pretty slow compared.

Progress update for June:

- Prototype PCB's for 1802, 8031, 8085 arrived.  Working on bringing up and SW.

- I did some clean-up in the existing code for 6502/6809/Z80.  Basically got rid of the timer-based execution and now Arduino will toggle clock as fast as possible. With all if/then/elses, I get 160~170kHz avg.

- I finished 128KB SPI-RAM + caching support and checked in code for all three processors. Microchip 23L1024 can use 4-bit SPI mode, vs 1-bit SPI. With caching enabled, things are fast enough. Working on a write-up so you can build one too.

Next steps:

- Bring-up 1802, 8031, 8085 code.  Need to study waveforms and monitor code.

- Investigating +12V and -5V power supply for 8080. Currently debating between using a 4-pin module or implement boost/inverting switching power supplies using discrete components (cost-wise they are wash, for our volumes :):).

- I've been thinking about an Arduino Shield that has 1) SPI-RAM (128KB), 2) SPI-FLASH (64KB), 3) RTC, 4) SD-Card, and 5) LCD-Display, and maybe 6) GPIOs, 7) floppy disk, 8) audio input/output. If we don't have to implement all of these, then there are existing SD/RTC shields which are cheap.

- 68008 will take more gpio's then available. I'm looking into GPIO extenders (SPI or I2C based) and/or build a bigger PCB that uses more of Arduino GPIO's.

- Wildcard project: to have a SID shield so I can play C64 tunes :)

So with 8080 and 68008, I think we will have major processors supported.

All design files are on GitLab: https://gitlab.com/8bitforce

Enjoy your summer,

Erturk

Progress update for May:

Just a reminder: it is very easy to build RetroShield yourself: use a bread-board and jumper the microprocessor to Arduino Mega.  you need about 40 jumpers and can be done in an hour (a reader did it).  If you have any microprocessors laying around, I suggest you do this. Let's keep those 8-bit legged creatures running.

Mailing list:

==========

I created a mailing list at YahooGroups: RetroShield.  Hard to tell if there will be enough interest, but if people sign-up and we get a good crowd, we can continue the discussion over there. If you have suggestions for other medium for discussion, we can try that too.

Request for help:

===================

- Anybody interested in bringing up RetroShield 1802?

- Anybody interested in bringing up RetroShield 8085?

- Anybody interested in bringing up RetroShield 8031?

- Anybody interested in bringing up Micro BASIC for Z80?

Hardware:

=========

1) I completed designs for three more processors (8031, 8085, 1802) and in a few days, I will send them to fab house.

2) Please review schematics and layout files if you can.  A few extra set of eyes are always useful to catch errors or make improvements.

3) 128KB RAM support: I brought up 23L1024 SPI-RAM.  I get nice fast 128KB RAM using Serial-Quad-Interface (4bits/clock cycle).  I am testing the cache now :)  Then I want to bring up Flex OS for 6809, my favorite processor.

4) Arduino Due: I brought up Western Digital W65C02S (3.3V compatible) using existing 6502 RetroShield (which is compatible w/ W65C02S) on Arduino Due.  Memory-wise we get 64KB but speed benefit is not there.  Why?  Because the ATMEL port assignments to GPIO headers are not sequential :(  Even if I redo and optimize Arduino-processor connections, I still need to do multiple shift/OR/AND operations to form 8-bit and 16-bit buses. In the end, I end up with Arduino Mega speeds. Maybe this is why I didn't focus on due in the beginning. My next step is to look at Raspberry PI connections and if we are going to do level shifting, it might be worth doing it on Raspberry PI.  (Having said that, my goal is to keep the project simple and easy for others to play with 8-bit microprocessors, so I feel using raspberry pi + level shifters is becoming a more complicated task. Anyways, this topic is open for feedback / suggestions.)

- An interested reader is designing RetroShield for Z8.

Software:

========

1) A draft working version of Z80 Efex monitor w/ assembler + disassembler is checked in. This monitor was done by friend who has been working on Z80 and 8085 SBC boards, inspired by Simon6809. Monitor can assemble and disassemble which is cool. His hackaday.io link:

https://hackaday.io/project/21044-z80-monitor-type-operating-system-and-sbc

2) I checked in KIM-1 emulator for 6502.  This version uses TTY for input/output and emulates 6530 timers.  Want to play chess :)

3) Faster speed: I moved the processor code from timer into loop() so it gets executed back to back, without any stack push/pulls.  I get about 165kHz now.  Code is checked in as "k65c02_apple1_faster".

Misc:

=====

- 6502 is becoming difficult to source (either price is high or chips don't work reliably).  I'm considering switching to Western Digital W65C02S instead.  I know this is not the authentic retro experience (as some readers mentioned), but it is better than nothing and has the benefit of being compatible w/ Arduino Due.

What's next:

===========

1) RetroShields for 8080 and 68008.

2) Prepare for 1802, 8085, and 8031 bring-up.

That's all for now; enjoy the summer.

Hi all,

Thanks for all kind words. I owe you guys an update. Plus, it forces me to make progress :)

Let me summarize feedback and then talk about what I'm working on:

Feedback:

- emulate KIM-1 for 6502

- investigate Arduino Due (faster, more RAM, but requires 3.3V<->5.0V level shifters)

- optimize Arduino code (should run faster than 100kHz).

- map Arduino GPIO's to microprocessor world.

- how can we add floppy support?

- more articles (geda/schem setup, how to assemble code, Z80 operating details)

- combine processors into one pcb

- more processor support (68008, 1802, 8031, 8085, 8080, Z8).

- In need of a good Z80 monitor

I checked in Arduino code that emulates KIM-1 via serial port. New thing was RRIOT 6530 chip (ROM-RAM-I/O-Timer). Initially I was going to emulate serial at the port level (i.e. bit bang the 6530 pins) but I ended up cheating by overwriting the ROM TTY subroutines to use a FTDI style serial port.  Having said that, I think it will be fun to emulate the serial port at the port level, in both directions!  I also got physical keyboard and 7-segment displays.  future project to connect these for a more authentic KIM-1 experience.  Oh, I forgot to tell.  Erik who knows a lot of KIM-1 and has a website (http://users.telenet.be/kim1-6502/).  He asked if we can feed KIM-1 audio files. Googling around, it looks like this is possible.  (KIM-1 audio files can be put on an SDCARD and then fed into the RRIOT pins).

While looking for KIM-1 information, I found a very cool project: a soft-6502 core for Arduino. (http://forum.arduino.cc/index.php?topic=193216.0).  It runs Commodore 64 BASIC :)  There is a post mentioning 2.2MHz emulated speed.  I need to join that discussion and find out the conditions, because Arduino Mega 2560 runs at 16MHz and assuming 1-cycle/instruction I need to toggle the microprocessor clock twice within 16 cycles.  So I have 14 cycles left to do several if/then/elses and keep track of registers, timers, etc to emulate devices.  I am not optimistic we will get 1Mhz on Arduino Mega 2560.  Having said that, I made changes to run faster than 100kHz. The microprocessor loop was running in timer1() loop.  Timer1 is an interrupt handler so it involves stack operations wasting Arduino cycles. I moved the uP loop into the Arduino main loop() and I got ~165 kHz.  This is promising.  The interim code is checked under k65c02_apple1_faster/.  I will continue to work on this.

-I was bugging my friend to send me his Z80 monitor. He finally did today. This should be released under RetroShield Z80 soon.

- 8031 and 8085A schematics started.

- Level shifter IC's and SPI RAM chips (128KB) arrived. First task is to increase the RAM available on Arduino Mega. Next level shifters with Due.

- added an article (on my blog) that explains how to assemble your own firmware.

This is amazing!

With Arduino Due + bidirectional level shifters such as 74lvc245 you will get better performances.

Please include support for NCR 53(C)80 scsi controller and for some controller able to handle 8"+5.25"+3.5" floppy drives.