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mahjongg
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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Tue May 07, 2019 12:16 am

scruss wrote:
Mon May 06, 2019 1:25 pm
good use of machine-pin sockets there!
but what happened to that poor d-sub connector: burning? dremel? a dremel that caught fire? :D
An accident with the soldering iron, while trying to remove R27 without damaging the board, its just some melted plastic, this is a prototype after all, its not there to win beauty contests, and accidents happen.

when you chop wood splinters will fall... :mrgreen:

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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Tue May 28, 2019 10:33 pm

Well I managed an important step forward, I am able to generate a VGA text video signal!
This was a necessary step because without some form of built in text terminal it would be hard to develop and debug software, both for the P8X32A (propeller) co-processor, as for the Z80 main CPU. no hardware modifications were necessary, just a modified VGA.SPIN driver, and a simple .SPIN terminal routine.

A much better tile based high-resolution video driver will come later.

Image

Another important step will be gaining file access from the SD-card. For that I need to first get the I2C I/O expander chip (PCF8574A) working, then implement a rudimentary SD-card driver.

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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Tue May 28, 2019 11:34 pm

That is a nice looking font.
Need Pi spray - these things are breeding in my house...

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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Wed May 29, 2019 8:41 am

Andyroo wrote:
Tue May 28, 2019 11:34 pm
That is a nice looking font.
Its the default font built into the P8X32A, its 16 x 16 pixels, so yes it looks good.

P.S. Its using half the 32K ROM space of the propeller, so 16K byte.
by the way, I found out that the real VGA resolution used is 640 x 480, this means the text screen only is 15 lines, not 16 as was documented, and the actual pixel width used is 512 pixels, at least in this 32 x 15 VGA text driver.

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Gavinmc42
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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Wed May 29, 2019 8:53 am

Prop2 does HDMI?
Will be hard to find VGA monitors soon, they are becoming retro too?

The Prop1 can do quite some graphics considering the limited ram.

That post of the 4014 terminal on a PiDP11 dragged out some old memories ;)
This one brought back the Prop1 video memories which is looking retro too now :lol:
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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Wed May 29, 2019 12:37 pm

AFAIK Prop2 is still not out, I don't expect it to do HDMI, so yes, I'm using a Prop1, and as it will mainly be used as a video generator I can use most of its 32K for a video framebuffer. The Z80 will have its own main video memory, and typically it will be something like 10K.
When Prop2 comes out I consider it for an upgraded Rhococo.

The current video driver is just a modified standard VGA video text mode driver, just for software development.

So yes its VGA, which is already a big step up from just generating a composite video signal.

most modern monitors still accept VGA, and there are literally millions of VGA capable monitors still in use, so not having HDMI isn't much of a compromise. I expect that (second hand) VGA capable monitors will be easily be available for another few decades, not so much TV's with a composite input...

Remember this is a device that is RETRO to the core... :mrgreen:

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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Wed May 29, 2019 4:37 pm

Gavinmc42 wrote:
Wed May 29, 2019 8:53 am
Prop2 does HDMI?
I believe so; it was a late addition to the spec - And what isn't with the P2 ? :roll:

From my understanding it will generate standard HDMI but won't have a full 1920x1080 framebuffer. I would guess it probably supports 360p.

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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Wed May 29, 2019 5:37 pm

It seems a prop2 is definitely overkill for my retro home computer.
But its nice to know they are working on it, and I will definitely be keeping an eye on it.

for now a prop1 can bring me all these things:
  • providing permanent memory, in the form of a cheap serial EEPROM
  • Loading up ROM images to the Z80's RAM, booting them up, handling and generating the Z80 clock signal.
  • Handling Z80 IORQ's (up to 256 unique read and write requests)
  • handling background NMI's for the Z80, and copying the Z80 frame buffer RAM to the propeller for display
  • handling (triggering) periodical keyboard matrix scans and reads, converting them to key-press and key-release codes, plus handling the keyboard buffer
  • initializing and handling the 8_blocks_of_16K memory mapper for the 128K Z80 RAM (expandable to 256K).
  • handling sound generator emulation (including a SID chip, and AY8910 sound)
  • generating a 64 color VGA signal with various text and tile based graphics modes, including sprites
  • assisting in fast vertical and horizontal scrolling
  • Handling SD-card file I/O , loading files in Z80 ram, and executing them, if needed.
  • handling software updates for both the Z80 and propeller co-processor.
  • providing UART and I2C I/O capabilities, for I/O expansion and a programming/debug interface
  • And probably a whole lot of other tasks I have not thought of yet

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Gavinmc42
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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Sat Jun 01, 2019 11:00 am

most modern monitors still accept VGA, and there are literally millions of VGA capable monitors still in use, so not having HDMI isn't much of a compromise.
This was in my head when I saw a HDMI to VGA dongle in Daiso the other day.
Did not even know they make those sorts of things.
$25 AUD a bit higher than usual Daiso pricing.

i wonder how the Prop would go as a Hyperbus memory interface?
F-RAMs? 100 Trillion R/W cycles 108MHZ QSPI:o
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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Sun Jun 02, 2019 6:26 am

mahjongg wrote:
Wed May 29, 2019 5:37 pm
for now a prop1 can bring me all these things:
  • providing permanent memory, in the form of a cheap serial EEPROM
  • Loading up ROM images to the Z80's RAM, booting them up, handling and generating the Z80 clock signal.
  • Handling Z80 IORQ's (up to 256 unique read and write requests)
  • handling background NMI's for the Z80, and copying the Z80 frame buffer RAM to the propeller for display
  • handling (triggering) periodical keyboard matrix scans and reads, converting them to key-press and key-release codes, plus handling the keyboard buffer
  • initializing and handling the 8_blocks_of_16K memory mapper for the 128K Z80 RAM (expandable to 256K).
  • handling sound generator emulation (including a SID chip, and AY8910 sound)
  • generating a 64 color VGA signal with various text and tile based graphics modes, including sprites
  • assisting in fast vertical and horizontal scrolling
  • Handling SD-card file I/O , loading files in Z80 ram, and executing them, if needed.
  • handling software updates for both the Z80 and propeller co-processor.
  • providing UART and I2C I/O capabilities, for I/O expansion and a programming/debug interface
  • And probably a whole lot of other tasks I have not thought of yet
You may find it more than a little challenging implementing all of the above in a single Prop. VGA with sprites alone is likely to use at least half the cogs.

I managed to use all eight cogs for a simple USB to matrix keyboard interface, although in that case I was not trying to be economical :)

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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Sun Jun 02, 2019 7:04 pm

Memotech Bill wrote:
Sun Jun 02, 2019 6:26 am
You may find it more than a little challenging implementing all of the above in a single Prop. VGA with sprites alone is likely to use at least half the cogs.

I managed to use all eight cogs for a simple USB to matrix keyboard interface, although in that case I was not trying to be economical :)
yeah, I know.

it would be nice if there was a prop1 with just a few more cogs, and maybe a bit more memory, alas, the prop2 went a completely different way.

we will see how far I will get, mainly with swapping tasks for the same cog.

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Re: My own 8-bit RETRO Homecomputer: RhoCoCo

Tue Jun 11, 2019 10:46 pm

I have gotten the I2C PCF8574A IO-expander chip, ( the IO expander that drives the SD-card interface ) working (I can now write to, and read from the expanded I/O ports) and I have also solved a nasty resetting problem.

when you inserted an SD-card into the SD-card slot the system would reset due to the in-rushing-current generated by suddenly loading the card across the 3V3 supply. I changed the decoupling capacitor (C13, 100nF) to a 470uF 6V3 elco, and that solved the resets, the rush-in current is now delivered by this elco, and so the 3V3 supply doesn't "dip" anymore, solving the brownout resets.

I changed the schematics, and PCB layout to revision 2.1 with this change in C13, from a 2/10" cap to a 6.3mm round 2mm pitch elco.

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