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Powertran Cortex

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    Originally posted by ClassicHasClass View Post
    Nice. Do you have an image of UNIX V6?
    Do you mean a disk image? A screen shot?

    Comment


      Disk image, yes.
      I use my C128 because I am an ornery, stubborn, retro grouch. -- Bob Masse
      Various projects and oddities: http://oldvcr.blogspot.com/
      Machine room: http://www.floodgap.com/etc/machines.html

      Comment


        Originally posted by ClassicHasClass View Post
        Disk image, yes.
        Sure, please pm me with your e-mail and I'll send you a disk image and an updated emulator (the one from last year did not yet emulate the mapper chip). Still finding the odd bug, but all the most common facilities appear to work fine.

        Paul

        Comment


          Done. Thanks!
          I use my C128 because I am an ornery, stubborn, retro grouch. -- Bob Masse
          Various projects and oddities: http://oldvcr.blogspot.com/
          Machine room: http://www.floodgap.com/etc/machines.html

          Comment


            Hello everyone! This is posting is about TMS9995 meeting Xilinx Spartan 6 FPGA.

            I've been tinkering with my version of Stuart's TMS9995 breadboard computer for a short while. I got it to work about two weeks ago and got in touch with Stuart to thank him for the nice design and website (and to ask a few questions), and he provided me with a link to this thread. Since then I've been continuing a little my work, and I thought it's now far enough to write this post about it. This is my very first forum posting so I hope formatting turns out readable.

            I also do hope this thread is still alive - there's very nice stuff here, I have only read a small fraction of the material, but it is very impressive and I'm looking forward to reading the thread in its entirety.

            Basically my board can be summarized now as TMS9995 meets Xilinx Spartan 6 FPGA, picture below. The nice thing about working with breadboard computers is that it is so easy to modify them. So I started my version (indeed before being aware of this thread and the cortex mini board) by basically hooking up TMS9995, FLASH ROM, TMS9901 parallel interface and a GAL22V10 to do address decoding, while waiting for a bunch of TMS9902 UARTs to arrive from china. Since with the chips I got I could quite replicate Stuart's original design, I just ended up writing some TMS9900 assembly code to test the board and got LEDs blinking with the TMS9901. When the UARTs did arrive (a month from order - I ordered them before starting the build) I then decided to first test the UART before wiring up the SRAM. Luckily the TMS9902 chips I got turned out to be in working order, so I was able to communicate with the TMS9995 and finally fulfill the blank in my childhood of not being able to write assembly code for my TI99/4A - I was a bit too young to realize I should have bought mini memory card bridgerather than extended basic...

            Well to come back to this story, I got Stuart's design to work and tested things a little. I noticed that to my surprise the old TI chips would run at surprisingly low voltages. From by bench power supply I was able to go to as low 3.4V before the breadboard stopped working. I was amazed, but I also realized I could directly hook up 3.3V chips without frying them. This is the point in time I reached out to Stuart, and got the pointer to this thread. He kindly also posted me the schematics of the Cortex mini. I started to think that this would be the perfect opportunity to implement a strange version of the cortex mini. So I removed the GAL chip, hooked one of my FPGA boards to the GAL's pins and reimplemented the address decoding logic in the FPGA. That all worked. Encouraged by that, I proceeded to implement more logic into the FPGA. I have not gone very far yet on that path, but most of the logic on the cortex mini is now working in this implementation; namely I wrote an implementation of something like the 64LS612 in VHDL while trying to keep this compatible with the cortex mini.

            To summarize, my board contains the TMS9995, 256K FLASH, 512K SRAM, TMS9901 and TMS9902. The FPGA implements a reset circuit, the MMU, the "flags" register in the cortex mini (the two blue less on the FPGA board indicate that ROM overlay is turned off and MMU paging is turned on - I wrote a short piece of code in BASIC to replicate the reset conditions with the MMU paging turned on).

            I think I'll finish here for now, to see if this thread is still active and if this design sparks some interest. For me this has been a very rewarding project so far and I will definitely continue on it. Next on the agenda will be the implementation of an SPI controller in the FPGA to support SD cards, and then probably some kind of a VGA controller. The Unix stuff discussed in this thread is very interesting, I'd like to get that running on my board too.
            tms9995spartan6.jpg

            Comment


              We are definitely still here--and active. This thread has become one of the major Powertran Cortex resources on the Internet, and it makes me glad I started asking questions about the system when I did. The breadboard systems are most interesting too, although I still have to take time to sit down and build one. A lot of what you are doing with the FPGA may also easily translate to the 99/4A, as the SAMS memory card also uses the 74LS612 Mapper chip. . .
              Enter My Mind At Your Own Risk!

              Comment


                Hi Speccy,

                Welcome to this thread and what an interesting first post! Just when I thought this thread had gone about as far as it possibly could, you are introducing new and intriguing views. Could you elaborate more on the features of your FPGA & prototyping board and how you are hooking it up?

                The TI chips being able to run at 3.4 volts opens all sorts of possibilities. I wonder if that holds for the TMS99105 CPU too.

                For a while I have been thinking about doing a new revision of the mini Cortex board but never could quite decide what to put in it. In the mean time I was moving forward with software so that I could get a clearer picture of what hardware features would be desirable. One line of work involved putting V6 Unix on the TI990 minis (most credit goes to Dave Pitts) and looking into adding a TCP/IP stack to the Unix code. Last but not least I was thinking ahead about a 99105 based system.

                Your concept opens up a new horizons. The Cortex cannot run most software for the TI minis because the MMU design is quite different and the TI990 MMU is too complex to build with a few 74 series chips. It would be quite feasible to implement in an FPGA, possibly even switching between "Cortex mode" and "TI990 mode". Also, for the 99105 board I was thinking about putting in two 612 chips (one for kernel mode, one for user mode), and having this in an FPGA would be cleaner. As you already pointed out, it will also be a good route to adding SD Card mass storage. A CF card is very easy to interface, but CF cards have become vintage parts in the last few years. The FPGA could also do disk DMA. In short, tons of new ideas become possible.

                If you need input on making Unix run on your board just holler and I'll do my best to help. The coming weeks I'm quite busy though (I'm having the roof reconstructed).

                Paul

                Comment


                  Originally posted by Ksarul View Post
                  We are definitely still here--and active. This thread has become one of the major Powertran Cortex resources on the Internet, and it makes me glad I started asking questions about the system when I did. The breadboard systems are most interesting too, although I still have to take time to sit down and build one. A lot of what you are doing with the FPGA may also easily translate to the 99/4A, as the SAMS memory card also uses the 74LS612 Mapper chip. . .
                  Hi Ksarul,
                  I am glad you guys are still there and active! I'm equally glad that the people here are pretty liberal in what you define as a powertran Cortex and that breadboards qualify.

                  On my side I don't quite remember when I first stumbled across Stuart's site, but when I did I did order a few parts in the hope of eventually building up to TI99/4A clone. Then home renovation happened and I didn't have any spare time and I kind of forgot the parts until I recently rediscovered them. Certainly going the FPGA route opens up plenty of possibilities, the same basic electrical design can take very many forms.

                  Comment


                    Hi Paul,
                    Thank you for the message, I'm glad to have found my way here.

                    I'd be happy to share what I've done in more detail. As an aside, for some reason it is nice to talk to people who appreciate this sort of thing, explaining to my wife what I am spending some of my hours on is sometimes a bit hard (by the way, after thinking about that over the years, I've concluded that for me building these things is relaxing as one can effectively control everything in this small but fascinating world of, well, breadboards in this case; real world tends to be so much more complex).

                    I've been gathering a collection of small and cheap FPGA boards to try different things on, mostly by ordering from China through ebay. I've been wanting to hook up one of these to CPUs like the TMS9995 for a long while, but dealing with voltage level converters for nearly all signals has increased the entry to barrier for this type of a project. I also got distracted by going to full soft-CPU implementations instead of connecting the FPGA boards to real computers; I built a ZX Spectrum clone on a few different FPGA boards.

                    The board I'm using in this case is this one:
                    http://www.ebay.com/itm/Xilinx-XC6SL...oAAOSw-7RVF8vl
                    "Xilinx XC6SLX9 Spartan 6 FPGA Core Board, Nano Size"
                    This board is nice due to a few reasons: the FPGA is pretty sizable (more on that below), it integrates an SPI Flash chip for FPGA configuration data (well most boards like this do) but mostly because it includes an FT232RL chip, enabling the board to be powered off from USB and providing a logic level serial port for the FPGA. In my case I just route the FTDI's TX and RX signals out to the FPGA's pins connected to TMS9902; at this point the FPGA does nothing with the data (well it also drives the on-board LEDs to show that traffic is going through).
                    The notable omission on the board is the lack of programming hardware to download the FPGA design; there is a JTAG connector but you need an external programmer device to drive it. In my case I bought I programmer (also from ebay), it works well and enables to use these low cost FPGA boards. I have a few more expensive boards which have built-in programming circuitry, but I think I prefer these cheap boards especially when messing with breadboard wiring - if the smoke decides to come out, the damage will be smaller...

                    The LX9 part is second to smallest in the Spartan 6 range. Still, it is by no means a small chip. To give you some idea, it can accommodate an entire ZX Spectrum with ease (including the CPU and all the memory - it's got 32 dual port memory blocks of 18kbits each, basically 64K of RAM); I also downloaded and adapted the Scramble arcade machine clone for another LX9 board, also only using on-chip resources. The Scramble system has two Z80 cores, plus a video system including sprite capabilities, and consumed about 70% of the resources of the FPGA.

                    But to come back to this design, once I realized that level converters would not be necessary, I started to test things and I am now at a point where literally on the breadboard there are only the "essential" chips: TMS9995, FLASH ROM, SRAM, TMS9901 and TMS9902. The FPGA is by now connected to nearly all of the pins of the CPU, and it drives the chip select signals to all the other chips. I actually just finished implementing the NMI generator to enable single stepping, and therefore added a few more wires (NMI and IAQ). That is actually somewhat illustrative of the design process: once the basic functionality is there, it nice that I can just edit a little the VHDL code, synthesize and upload it to the FPGA, add a couple more wires - and I've got a new feature in the system.

                    Right now the design implements the '612 design (to my understanding as implemented in the mini cortex), external instruction decoding, the LREX->NMI logic, address decode etc. and the logic is usage is still at 1% of the capacity of this FPGA. Also the design does not use any of the memories - or the DSP units (there are 16 very fast multiply-accumulate units on board, also it has a few sophisticated clock synthesizers that are not used at the moment). If you're interested I can post the VHDL code; although I have to say I'm not an expert on VHDL. (Getting things to work has been good enough for me... I'm much more a C++ / assembly guy, but you just cannot use those skills alone to create hardware.)

                    With that, it certainly is possible to implement very complex MMU designs. My plan is to indeed add support for SD cards, I've already half-done done that in another project so it should not be too hard. Also I think it would be a nice exercise to implement TMS9918 functionality, and perhaps emulation, which would enable this thing to transform both into an "actual" Cortex and TI99/4A.

                    I also happen to have one TMS99105 chip. I'm very intrigued of the idea of hooking it directly to an FPGA, so that the address demultiplexers and memory buses could just exist inside the FPGA - there would be a lot less wiring that way.

                    I think I am going to need some help to get your Unix running - although I have not yet extensively read this great thread, so I don't really have an idea on how much ground has already been covered in the messages. Anyway I want (and probably need) to get some kind of mass storage working first, and I also want to get more familiar with Stuart's port of the firmware. As a simple but hopefully useful exercise I was planning to add to Cortex basic save&load functionality to the Flash rom. The basic interpreter is a pretty handy hardware testbed.

                    I have feeling this has already gotten a pretty long posting, hopefully the browser doesn't choke before it is posted...

                    Erik

                    Comment


                      A few more comments...

                      Originally posted by pnr View Post
                      For a while I have been thinking about doing a new revision of the mini Cortex board but never could quite decide what to put in it. In the mean time I was moving forward with software so that I could get a clearer picture of what hardware features would be desirable. One line of work involved putting V6 Unix on the TI990 minis (most credit goes to Dave Pitts) and looking into adding a TCP/IP stack to the Unix code. Last but not least I was thinking ahead about a 99105 based system.
                      Those sound interesting project ideas. Do you have some pointers to go to look for more info on the TI990 minis and their MMU? Well I guess I should google them up...

                      Erik

                      Comment


                        Originally posted by speccy View Post
                        The notable omission on the board is the lack of programming hardware to download the FPGA design; there is a JTAG connector but you need an external programmer device to drive it. In my case I bought I programmer (also from ebay), it works well and enables to use these low cost FPGA boards. I have a few more expensive boards which have built-in programming circuitry, but I think I prefer these cheap boards especially when messing with breadboard wiring - if the smoke decides to come out, the damage will be smaller...
                        OK. Diligent sell a very convenient JTAG cable as well, although somewhat more expensive than Chinese boxes: https://store.digilentinc.com/jtag-h...ramming-cable/
                        It looks like this board can be piggy backed onto another PCB -- my eyes are too old to solder anything below 0.1" I think. Are those GPIO connectors on both sides, i.e. some 80 I/O pins freely available?

                        Originally posted by speccy View Post
                        But to come back to this design, once I realized that level converters would not be necessary,
                        Are you running the system at 3.4V? Or a bit more to be stable, 3.6V or so? Does it still run at 3MHz (12MHz crystal)?

                        Originally posted by speccy View Post
                        If you're interested I can post the VHDL code; although I have to say I'm not an expert on VHDL. (Getting things to work has been good enough for me... I'm much more a C++ / assembly guy, but you just cannot use those skills alone to create hardware.)
                        Yes, I'd be interested. Would it make sense to host the VDHL source at GitHub or so? That way there is a clear development history available for future readers. I've been thinking about learning VHDL for years but never got around to it. Perhaps 2016 will be the year.

                        Originally posted by speccy View Post
                        Also I think it would be a nice exercise to implement TMS9918 functionality, and perhaps emulation, which would enable this thing to transform both into an "actual" Cortex and TI99/4A.
                        Actually, the mini Cortex board already has a socket for the "F18A", a custom breakout board with a Xilinx XC3 FPGA and a few level shifters, that implements a 9918 chip with VGA output. Later versions also include a 9900 core. The F18A is the brain child of Matthew Hagerty: http://codehackcreate.com/
                        I'm not sure it is open source, but it might be.

                        Originally posted by speccy View Post
                        I also happen to have one TMS99105 chip. I'm very intrigued of the idea of hooking it directly to an FPGA, so that the address demultiplexers and memory buses could just exist inside the FPGA - there would be a lot less wiring that way.
                        Yup, my thinking exactly.

                        Originally posted by speccy View Post
                        I think I am going to need some help to get your Unix running - although I have not yet extensively read this great thread, so I don't really have an idea on how much ground has already been covered in the messages. Anyway I want (and probably need) to get some kind of mass storage working first, and I also want to get more familiar with Stuart's port of the firmware.
                        Currently there is a pretty complete V6 Unix port for the mini Cortex. It could also run on a real Cortex, as long as it has been extended with a hard disk. The source code repository is here:
                        http://1587660.websites.xs4all.nl/cgi-bin/9995/timeline
                        I guess I have not documented how to get from source to a disk image, but that is easily explained once you get to it.

                        Originally posted by speccy View Post
                        As a simple but hopefully useful exercise I was planning to add to Cortex basic save&load functionality to the Flash rom. The basic interpreter is a pretty handy hardware testbed.
                        The disk I/O routines were a later add on to Cortex Basic. We did some work on reconstructing the source code (disassembly + new comments) about one year ago; it is in this thread. Yes, from my perspective integrating this into the ROM is very useful.

                        Paul

                        Comment


                          Originally posted by speccy View Post
                          Do you have some pointers to go to look for more info on the TI990 minis and their MMU? Well I guess I should google them up...
                          It is on bitsavers: http://bitsavers.informatik.uni-stut...de/pdf/ti/990/

                          In short the TI990 MMU is a segmentation design with 3 segments. There are 3 limit registers defining the length of each segment, and 3 corresponding base registers that define the base address in physical memory for each segment. This design is repeated 3 times, once for kernel mode, once for user mode and once for LDD/LDS instructions.

                          In the discrete logic implementation of the TI990 CPU this is implemented with a lot of latches for the registers and a ton of comparators and adders for the logic. See the "schematics" directory at bitsavers for details.

                          Now that I think about it more, it may be hard to run DNOS unmodified on a 9995 chip, perhaps this is something that can only be easily done on a 99105 chip.

                          Comment


                            Originally posted by pnr View Post
                            OK. Diligent sell a very convenient JTAG cable as well, although somewhat more expensive than Chinese boxes: https://store.digilentinc.com/jtag-h...ramming-cable/
                            Yes, I think I actually was looking at these a while back but they were out of stock at the time. I would much rather go for one of these than any Chinese boxes. In fact I acquired an Estonian board that emulates the Xilinx cable, allowing it be used directly from Xilinx's Impact software. I live in Finland so that was close to me, it arrived in a few days. I have a Diligent board (Nexys2) and their products are solid. One thing I don't know is whether the Digilent's adept 2 software supports programming of the SPI connected flash ROM on this Spartan 6 board. The spartan 6 supports a kind of "sideband" SPI bus for boot up, and the Xilinx's impact programming suite allows one to easily program the flash and select the memory type on that SPI bus. This process is explained in the manual of the FPGA board.

                            Originally posted by pnr View Post
                            It looks like this board can be piggy backed onto another PCB -- my eyes are too old to solder anything below 0.1" I think. Are those GPIO connectors on both sides, i.e. some 80 I/O pins freely available?
                            A good point, you are right. Indeed perhaps the best feature of the board is that those pins are readily available. It was very late when I was writing my post so I didn't mention this - I also realized that there were some words missing in my post. I guess it was still understandable. There are indeed two 40 pin connectors, making the board piggy backable. I forget the exact number of useable IO, it's probably around 72 as there are some power pins in there.

                            Originally posted by pnr View Post
                            Are you running the system at 3.4V? Or a bit more to be stable, 3.6V or so? Does it still run at 3MHz (12MHz crystal)?
                            Yep, I am running at 3.6V and 3MHz, i.e. with 12MHz crystal. The FPGA already attempts to assert READY low before taking RESET high so zero wait states should work, but I haven't tested that yet, as I understand I may need to modify the firmware first to fix the baud rate of the UART.

                            Originally posted by pnr View Post
                            Yes, I'd be interested. Would it make sense to host the VDHL source at GitHub or so? That way there is a clear development history available for future readers. I've been thinking about learning VHDL for years but never got around to it. Perhaps 2016 will be the year.
                            A good idea, perhaps 2016 will be the year for me to finally get something posted on github I'll try to set it up.

                            Originally posted by pnr View Post
                            Actually, the mini Cortex board already has a socket for the "F18A", a custom breakout board with a Xilinx XC3 FPGA and a few level shifters, that implements a 9918 chip with VGA output. Later versions also include a 9900 core. The F18A is the brain child of Matthew Hagerty: http://codehackcreate.com/
                            I'm not sure it is open source, but it might be.
                            This is a very nice project, but to my understanding it is closed source. Haven't checked recently though.

                            Originally posted by pnr View Post
                            Currently there is a pretty complete V6 Unix port for the mini Cortex. It could also run on a real Cortex, as long as it has been extended with a hard disk. The source code repository is here:
                            http://1587660.websites.xs4all.nl/cgi-bin/9995/timeline
                            I guess I have not documented how to get from source to a disk image, but that is easily explained once you get to it.
                            Thanks, I'll take a look.

                            Originally posted by pnr View Post
                            The disk I/O routines were a later add on to Cortex Basic. We did some work on reconstructing the source code (disassembly + new comments) about one year ago; it is in this thread. Yes, from my perspective integrating this into the ROM is very useful.
                            Cool, I need to take a look at this too. It seems there is a fair bit of follow up to do. I don't know when I'll have the time for all of that, but I',m looking forward to it. Certainly you guys have done a lot of interesting stuff here!

                            Erik

                            Comment


                              Originally posted by speccy View Post
                              In fact I acquired an Estonian board that emulates the Xilinx cable, allowing it be used directly from Xilinx's Impact software. I live in Finland so that was close to me, it arrived in a few days. I have a Diligent board (Nexys2) and their products are solid. One thing I don't know is whether the Digilent's adept 2 software supports programming of the SPI connected flash ROM on this Spartan 6 board. The spartan 6 supports a kind of "sideband" SPI bus for boot up, and the Xilinx's impact programming suite allows one to easily program the flash and select the memory type on that SPI bus. This process is explained in the manual of the FPGA board.
                              So what would you recommend I acquire if I want to experiment with a 99105 breadboard and an FPGA this Summer? I'm also based in the EU. (My understanding is that the 9918, the 9995 and the 99105 were all made in the same 5u NMOS process, so I think chances are that the 99105 will also run on 3.6V). The same Estonian board and the same Spartan 6 board?

                              Originally posted by speccy View Post
                              Cool, I need to take a look at this too. It seems there is a fair bit of follow up to do. I don't know when I'll have the time for all of that, but I'm looking forward to it.
                              All of this is hobby on a 'as time permits' basis. You will note that this thread often goes silent for many months until there is something meaningful to report, so don't feel pressurized in any way.

                              Comment


                                Originally posted by pnr View Post
                                So what would you recommend I acquire if I want to experiment with a 99105 breadboard and an FPGA this Summer? I'm also based in the EU. (My understanding is that the 9918, the 9995 and the 99105 were all made in the same 5u NMOS process, so I think chances are that the 99105 will also run on 3.6V). The same Estonian board and the same Spartan 6 board?
                                Interesting that they're all made on 5 micron process. I was earlier today wondering what might be the generational gap in terms of minimum feature size between Spartan 6 and the TMS9995.

                                The Estonian JTAG board does not seem to be anymore available. The eBay link to their store is http://www.ebay.com/usr/fpga.store but they seem to have very few products out there.
                                I think what you should get for this project with the TMS99105 are the Spartan 6 board and some reliable means of programming it, so that can focus your energy on doing something interesting instead of fighting with the setup. Probably the Diligent programming cable is a good choice.

                                In addition, as you are planning to learn VHDL and instantaneous gratification is normally a good thing, I would recommend that you also get an all-in-one board to test things on. This is a function of how much you are willing to spend. Although the Diligent boards are nice I would recommend either getting the Papilio Duo or the Pipistrello board. They are more affordable, have nice specs and some samples and support. I have both, but I haven't done much with the Pipistrello yet - other than using it as a logic analyzer with an additional adapter board they call "wings". The Pipistrello has a pretty sizable FPGA but is also more expensive. The Papilio Duo has the same XC6SLX9 FPGA which is on the Chinese board. I actually got started with Spartan 6 chips on the Papilio Duo, and then went for the cheap board. It might be possible to use the Papilio Duo as a programmer too for external FPGAs, at least it has a built in programming capability and easy to use software. Many of the Papilio examples are based on their ZPU based Arduino like environment. After a few quick tests I decided not to use any of that, and only used the FPGA loader program.

                                http://papilio.cc/index.php?n=Papili...OHardwareGuide

                                http://saanlima.com/store/index.php?...&product_id=51

                                I ordered another Spartan 6 board from China, I like to have a spare one if I happen to blow up the one I am now using. If I have some time before it arrives I may end up wiring my TMS99105 to the Papilio to see what happens.

                                Originally posted by pnr View Post
                                All of this is hobby on a 'as time permits' basis. You will note that this thread often goes silent for many months until there is something meaningful to report, so don't feel pressurized in any way.
                                Thanks for the comment, I kind of assumed as much. My intention is not to take any pressure on this, as this is supposed to be fun
                                At least for me these type of projects and my motivation go in cycles, also depending obviously on how much time there is for projects like this. Easter holidays are now over, so I don't know when I have some time and energy for this stuff. Luckily so far it has been possible to progress in small steps, getting some incremental results without investing too much time at one go.

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