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CRC65, a 6502 SBC [message #8231]

Sun, 24 January 2021 15:11

plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA

Senior Member

I hung around 6502.org lately working on a couple 6502-based computer designs. One design is in good shape now. I called it CRC65 (CPLD-RAM-CFdisk-6502). It is very similar to ZRCC in concept, i.e. CPLD contains a small boot ROM and a serial port; immediately after reset 6502 decides whether to boot from serial port or from CFdisk based on user input. It is a 2-layer board 50mm X 100mm. 14MHz W65C02 is slightly overclocked to 14.7MHz to get standard serial baud clock. Margin test shows the board can run to 22MHz, so I'm not worrying about 0.7MHz over the rated clock.

Clock-for-clock, 6502 is about twice as fast as Z80. So 14.7MHz 6502 is essentially a 30MHz Z80.

The design file is here. https://www.retrobrewcomputers.org/doku.php?id=builderpages: plasmo:crc65
Bill
/forum/index.php?t=getfile&id=1965&private=0

/forum/index.php?t=getfile&id=1965&private=0

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Re: CRC65, a 6502 SBC [message #8236 is a reply to message #8231]

Mon, 25 January 2021 03:27

just4fun
Messages: 273
Registered: May 2017
Location: Dark side of the Moon

Senior Member

Nice!

Do you thing that there might be any OS for it?

As far as I know there isn't any CP/M for a 6502...

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Re: CRC65, a 6502 SBC [message #8237 is a reply to message #8236]

Mon, 25 January 2021 05:18

plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA

Senior Member

No real CP/M for 6502, I think there is an experimental version, but I don't know how well it works. No dominant OS software I know of. BASIC and Forth are popular application software. Hardware design is simpler because the ROM & reset vector are top of memory separated from software critical region in low memory. There is no need for paging of ROM/RAM at low memory.
Bill

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Re: CRC65, a 6502 SBC [message #8322 is a reply to message #8237]

Wed, 17 February 2021 09:28

plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA

Senior Member

I updated the CPLD equations to fix write problem with certain brand of CF disks.
https://www.retrobrewcomputers.org/lib/exe/fetch.php?media=b uilderpages:plasmo:crc65:crc65_rev0_pcb_improved_cf_access_2 _12_21.zip

It is noteworthy that with faster CF disk, this design allows CRC65 to overclock W65C02 to 29.5MHz with performance comparable to 60MHz Z80!
Bill

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Re: CRC65, a 6502 SBC [message #8327 is a reply to message #8322]

Thu, 18 February 2021 01:29

simonj5
Messages: 13
Registered: October 2018
Location: Cambridge, UK

Junior Member

I have stumbled across DOS/65 on a site primarily focussed on the Z80[!] that claims 'DOS/65 - an interesting operating system with file system compatibility to CP/M-80 (and other similarities)'. Included on the site are instructions for 'bringing the system up'.

My CRC65 PCB has arrived from China and I'm collecting the other components so when I get time [yeah...] I'll have a go at assembling a CRC65 and get it running in the default configuration before, perhaps, having a go at producing a suitable DOS/65 disk image.

Incidentally Bill, on the 6502.org forum you hinted at some changes to VGARC that were needed to get it working with the modified RC2014 bus; I know that you are tremendously busy and have a work rate that puts me to shame but do you have an update on a VGARC update?

Simon

[Edited] A closer look at the site suggests that a lot of the work is done using a Z80-based cartridge... Perhaps time for a rethink Embarrassed

[Updated on: Thu, 18 February 2021 02:15]

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Re: CRC65, a 6502 SBC [message #8329 is a reply to message #8327]

Thu, 18 February 2021 07:26

plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA

Senior Member

Simon,
Thanks for the link to DOS/65. CRC65 method of booting off CF disk is more complicated than necessary, but I am hoping the presence of a CF disk would motivate myself and others to look into disk operating system of some sort for 6502. DOS/65 seems a step in the right direction.

The mapping of address lines on VGARC works with Z80's extended I/O addressing which essentially byte-swap the high-order addresses with the low-order addresses. To make it works for 6502, I need to cut the highest 4 addresses (A15 to A12) and wire it to A4-A7, so there are 4 cuts and 4 jumpers. I think a better solution is a new pc board with address A0-A11 to the dual port RAM. Such new design would work with 680x0, 6809, and 6502. I plan to make the 4 cuts and 4 jumpers just to make sure it all works for 6502 before I do the new board layout.

Bill

PS, please keep me updated regarding your status with CRC65. A fresh new pair of eyes is always informative. I welcome your comments and questions.

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Christmas Tree [message #9531 is a reply to message #8329]

Fri, 24 December 2021 20:00

plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA

Senior Member

Merry Christmas

/forum/index.php?t=getfile&id=2583&private=0

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Re: CRC65, a 6502 SBC [message #9699 is a reply to message #8322]

Sat, 29 January 2022 14:25

etchedpixels
Messages: 333
Registered: October 2015

Senior Member

If you use an 65C816 instead and run it in 16bit mode you'll get an instruction issue rate not much slower than 8bit mode and an actual throughput way way higher.

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Re: CRC65, a 6502 SBC [message #9700 is a reply to message #8327]

Sat, 29 January 2022 14:27

etchedpixels
Messages: 333
Registered: October 2015

Senior Member

simonj5 wrote on Thu, 18 February 2021 01:29

I have stumbled across DOS/65 on a site primarily focussed on the Z80[!] that claims 'DOS/65 - an interesting operating system with file system compatibility to CP/M-80 (and other similarities)'. Included on the site are instructions for 'bringing the system up'.

There's a newer ROM based and non shareware DOS/65 at https://github.com/floobydust/DOS-65-V3.03-ROM

it's a nice piece of work although the insanity of ElfOS on the 1802 has it beaten I think Cool

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Re: CRC65, a 6502 SBC [message #9701 is a reply to message #9699]

Sat, 29 January 2022 15:57

plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA

Senior Member

etchedpixels wrote on Sat, 29 January 2022 15:25

If you use an 65C816 instead and run it in 16bit mode you'll get an instruction issue rate not much slower than 8bit mode and an actual throughput way way higher.

W65C02 footprint is very similar to W65C816, so with a few cuts and jumpers, CRC65's 6502 can be replaced with 65816. I now have rev2 of CRC65 that accommodates both 6502 and 65816 with jumper changes and different CPLD program.

The picture of Christmas light is too dark to see, but the processor in that CRC65 was 65816. The array of WS2812B LED was driven by an obscure 65816 output pin, M/X. There was discussion on 6502.org about how to use the M/X pin and my contribution was to bit-bang it fast enough to generate the 800KHz pulse modulated bit stream to drive WS2812B.
http://forum.6502.org/viewtopic.php?f=4&t=6806&hilit =ws2812b&start=15#p89486
Bill

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Re: CRC65, a 6502 SBC [message #10160 is a reply to message #9701]

Sun, 06 November 2022 20:30

plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA

Senior Member

Version 3 of DOS/65 is successfully ported to CRC65. DOS/65 is a CP/M 2.2 clone for 6502 processor. It is created by Richard Leary who has released it as freeware under GNU General Public License V3. Beside the sources of DOS/65 in 6502 assembly, a number of supporting programs are also available as 6502 assembly codes. Programs such as editor, assembler, debug, super directory, BASIC compiler, BASIC interpreter, Xmodem, and others.

Porting DOS/65 to CRC65 is similar to porting CP/M to Z80 processors. A platform-specific BIOS (called SIM in DOS/65) is required to interface to the specific hardware. DOS/65 implemented on CRC65 has four 8-meg drives and a serial port at 115200. Like CP/M, interrupt processing is not required for DOS/65. CRC65 has 58K of RAM of which 52K is available as transient program area. DOS/65's disk format is compatible with CP/M so it is possible to read CP/M disk in DOS/65. This feature was useful initially to copy DOS/65 programs to CF disk before XMODEM file transfer was available.

Included in DOS/65 distribution is a MicroSoft BASIC interpreter comparable to CP/M's MBASIC80.COM. I have overclocked CRC65's 6502 to 29.5MHz similar to ZRCC overclock Z80 to 29.5MHz, so here is a comparison of mandelbrot benchmark executed by 29.5MHz Z80 with MBASIC80 vs. 29.5MHz 6502 with DOS/65 BASIC:

Z80 CP/M:115 seconds
6502 DOS/65: 51 seconds

Clock-for-clock, 6502 is about 2.2x faster than Z80

I have created a page of DOS/65 port for CRC65 here:
https://www.retrobrewcomputers.org/doku.php?id=builderpages: plasmo:crc65:dos65:dos65home
Bill
/forum/index.php?t=getfile&id=2823&private=0

/forum/index.php?t=getfile&id=2823&private=0

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