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Little CDP1802 never needed a DMA controller. Indeed, at no time it gives up control of the bus for any other devices, nor does it ever stop executing instructions. Instead, it throws in an extra bus cycle with every instruction when DMA is requested, does all the memory addressing itself and signals the device to put its byte onto the data bus or take it from the data bus. It is its own DMA controller and allows DMA for devices that normally would not be able to control the bus themselves.
On top of that, it also has another operating mode, the load mode. If you switch the processor into load mode after a reset, it will not execute any instructions, but serve DMA requests. This was used to read from the hex keyboard and at the same time to output the byte you had entered on the LED display. This way you could enter and run programs without any software and only simplest hardware involved.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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The only side I want to be on is the winning side.
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Don't worry if you are on my side. I have found a schematic for an 8 bit IDE controller that actually is a good compromise. It does not waste half of your space, does not appear to be too slow and does not go overboard on the hardware side. Sadly, this also rules out DMA because DMA is still only works with the 8 bit data bus. That can't be changed.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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Quote: Ok, then it's good old parallel ATA/IDE. The problem here is that even the oldest specification requires a 16 bit data bus. You can use it with an 8 bit bus, but then the upper 8 bits of every 16 bit word would be wasted
Unless you have enough time to get the whole word with a mux.
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Or a 8 bit register/latch. The only complication is that both have to work bidirectionally and DMA on the 8 bit side is out of the question. I have found a schematic for a controller, designed for a Z80 system. It uses latches for the upper half of the data word and the direct approach (a bidirectional bus driver) for the lower half. A good compromise. Less sacrifice, still a victory.
Here is a link: http://blog.retroleum.co.uk/gfx/v4_ide_interface_schematic.jpg[^]
The schematic is kind of small, but you can enlarge it by clicking on it. Now I only have to adapt the logic that enables the out puts of the latches and bus drivers or when the latches have to store their data bits. The z80 does these things a little differently than my processor, but that should not be much of a problem.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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Hello. Sorry about the big block of text.
You mentioned the CDP1802 and, from what I read, it already has 16bit address but they are time multiplexed in 8bit. The best you can have is to insert an 8bit flip-flop to store the high 8bit of the address (or the low 8bit, whichever is sent first). There is probably some signal (pin or pins) that it uses to indicate when the first 8bit are sent and when the second 8bit are sent. You will need that to synchronize storing the address (allowing/disallowing writing to the flip-flops).
Keep in mind that, with 16bit, the most memory you can address is 65536 positions of 8bit, or 64kB.
Filesystem wise you have to go with something supporting at most 16 bit, like FAT16. Anything 32bit, like FAT32, is off the table since you would have to emulate the 32bit processing and that would most certainly kill performance. Even FAT16 might not run very fast or at all.
My recommendation would be for you to implement a raw flat filesystem. Think of the storage device as a fixed length file that has two lists, one starting at the lowest address and stores free positions of storage and positions of the start of the files (and maybe data like names, dates,etc), and another list starting at the highest address with the content of the files stored in reverse order (it is less problematic to expand files to free storage positions assuming you leave free space after each file). If you don't like the content in reverse order switch the positions of the two lists, in which case the first list will be in reverse order.
On a computer, you would have to either write a program that could handle this custom filesystem or write a FUSE layer to handle it seemingly. Writing a program that simply exports/imports all files from/to the filesystem to the filesystem of the computer is the easiest.
Advanced tip on expanding storage by using more flip-flops if both the CPU and storage device supports the timing: setup four flip-flops (remember these are 8bit wide) in the following manner: The first will store the high 8bit of the first address. The second will store the low 8bit of the first address. The third will store the data of the first address. The fourth will store the high 8bit of the second address. The low 8bit of the second address is pass-through.
Now you can use this trick to address up to 40bit worth of storage positions. Independently of you wanting to read or write to storage, first do a write with the high 16bit part of the address (bit 0 to 15) as the address and the 8bit data as the next 8bit of the address (bit 16 to 23). Next do the actual read/write from storage by passing the low 16bit of the address (bit 24 to 39) as the address.
If you need even more storage, you can add one more write using three extra flip-flops and use it as a block addresser. This would allow you to address 40bit storage positions of 24bit blocks or 48bit storage positions with 16bit blocks depending how you want to view it.
I have done something similar a long time ago with an 8051 and a 256MB disk.
Good luck 
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Quote: You mentioned the CDP1802 and, from what I read, it already has 16bit address but they are time multiplexed in 8bit. The best you can have is to insert an 8bit flip-flop to store the high 8bit of the address (or the low 8bit, whichever is sent first). There is probably some signal (pin or pins) that it uses to indicate when the first 8bit are sent and when the second 8bit are sent. You will need that to synchronize storing the address (allowing/disallowing writing to the flip-flops).
You are right, latching the upper address bits is the first thing that's done in every bus cycle. Originally there were quite a few RAM and ROM chips that took only 8 address bits and the timing signal to latch the 16 address bits internally. These devices are now too small, too slow and almost impossible to get in any useful numbers, so an external latch has always been the standard. In the past this would have been a pair of 74C174s Or 40XX (CMOS!) or now (glimpsing at the breadboard) a single 74HC373.
Unfortunately we are talking about the data lines, not the address lines. The processor does not multiplex the data bus in any way. It's a strictly 8 bit CPU, quite unusual for a RISC processor.
Look at this IDE port for Z80 systems: An 8-bit IDE interface @ Retroleum[^]
That looks like a good compromise. Two reads or writes for every access to the disk controllers, once to the latches for the upper 8 data bits and a second one for the lower data bits to the bus 'HC245 bus driver. I need to adapt the decoding logic a little, because everything is done the Z80 way, but that's no real problem. Bit banging on a parallel port would be much slower and just ignoring the upper data bits would be extremely wasteful.
ElectronProgrammer wrote: Keep in mind that, with 16bit, the most memory you can address is 65536 positions of 8bit, or 64kB.
I expanded the address bus a little to 24 bit. So make that 16 Mb. 32 bit would also be no problem. Nothing special, just paged memory. A little detail of the processor's way to call subroutines allows me to hide the page switching, so that I can call code anywhere in that space without the processor noticing anything. Unfortunately that does not work for data, the stack, DMA or interrupts. For that, the page registers would have to be part of the processor.
ElectronProgrammer wrote: On a computer, you would have to either write a program that could handle this custom filesystem or write a FUSE layer to handle it seemingly. Writing a program that simply exports/imports all files from/to the filesystem to the filesystem of the computer is the easiest.
First things first. I will just get this working on the first prototype on the breadboard. Then I can build the second one with expanded memory (just 1 meg.  )and (hopefully) some mass storage device. Once that is built, I can still worry about the OS, the file system or comfort.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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The 74HC373 are similar to the kind of chips I used in my 8051 school project but it was a couple octal D flip-flops instead of latches because we really don't need the two inputs, set and reset, and it took less board space (less pins). Maybe 74HC574 or similar but I don't really remember. Maybe there are chips for 16bit now.
The 8051 I used is similar to the CDP1802 you are using. It had 16bit addresses multiplexed in 8bit and 8bit data without multiplexing. It had no type of memory management. Only supported instructions to read/write registry or external address with the first block of external addresses taken by the internal memory.
I do remember that I expanded the address from 16bit to 32bit and the data I used both 8bit and 32bit. The drive I used had a 32bit block mode that read 8bit at a time in burst.
Expanding the data bus, from the hardware point of view, is identical to expanding the address bus with just one difference. The data bus is bidirectional so you need flip-flops (or latches) facing each direction of communication, they need to have an high impedance output when not enabled and care must be taken to select the correct facing flip-flops.
That is basically what is shown in the link you posted. However, the circuit I used was a little simpler but used more wires. The circuit in the link appears to "shift-register" the data from the two 74HC574 via the 74HC245 to the CPU.
In my circuit I just had all 74HC574 connected to the bus and just enabled the one I wanted to read/write. I had that "chip enabling" automated by using an extra shift-register that would shift a single one and was reset at the beginning of every read/write. And disabled the write chips by negating the read/write pin.
Like you said, is just more reads or writes from the CPU perspective. But still faster than parallel port and way faster than the serial port I had to use in the project that followed.
1MB? That's luxury 
It's almost as much RAM as my favourite laptop has (compaq contura aero 4/25 with 4MB) 
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ElectronProgrammer wrote: The circuit in the link appears to "shift-register" the data from the two 74HC574 via the 74HC245 to the CPU.
Nah, it's just decoding two IO ports and generating the signals when to enable the outputs of the latches and the
ElectronProgrammer wrote: 1MB? That's luxury
This is just the second prototype. The 'real' one will have up to 16 Mb and up to 8 processors.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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Are you documenting your project anywhere public? I'd be interested in following your progress.
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I saw Bob's outfit and realized today must be something special. Looking it up on line I discovered July 1st celebrates the founding of the Chinese Communist Party[^] and thus, in celebration, he put on a lot of made-in-China garments!
Well - I'm glad that's settled.
| Ravings en masse^ |
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| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "If you are searching for perfection in others, then you seek disappointment. If you seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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Balboos was making a funny.
Social Media - A platform that makes it easier for the crazies to find each other.
Everyone is born right handed. Only the strongest overcome it.
Fight for left-handed rights and hand equality.
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ZurdoDev wrote: Balboos was making a funny.
And it looks like it was made in China, because Slacker is still waiting for it to be delivered! 
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放屁
| Ravings en masse^ |
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| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "If you are searching for perfection in others, then you seek disappointment. If you seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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Hey! Not in polite company...
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dandy72 wrote: in polite company...
That's where you get the most BANG for the buck.
| Ravings en masse^ |
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| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "If you are searching for perfection in others, then you seek disappointment. If you seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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Social Media - A platform that makes it easier for the crazies to find each other.
Everyone is born right handed. Only the strongest overcome it.
Fight for left-handed rights and hand equality.
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Nice.
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Sorry, I forgot to laugh.
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Well today is also National Joke Day, so you've hit a 2-in-1 there!
Tomorrow is World UFO Day, so I wonder if Bob will dress up like an alien to celebrate it?
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musefan wrote: Tomorrow is World UFO Day, so I wonder if Bob will dress up like an alien to celebrate it?
How many of our lounge posters will take the day off to celebrate (their national holiday?)
| Ravings en masse^ |
|---|
| "The difference between genius and stupidity is that genius has its limits." - Albert Einstein | | "If you are searching for perfection in others, then you seek disappointment. If you seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010 |
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W∴ Balboos, GHB wrote: How many of our lounge posters will take the day off to celebrate (their national holiday?)
Not sure, allow me to escalate your query back to mothership and I will get back to you.
*music starts playing*
please hold... your domination is important to us.
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Celt used around selection (8)
"We can't stop here - this is bat country" - Hunter S Thompson - RIP
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