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Thread: Powertran Cortex

  1. #601

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    {Stuart} The 9995 data manual shows a gate of a 7407 connected between /RESET and READY to achieve this.
    probably a diode will do instead so /reset pulls down ready


    {Stuart} Not that I'm aware of. What I've done before though is get the micro to continually send a short text string as it increments and prints the baud rate value. When you see the text string correctly, read the baud rate.

    what is the issue with baud rate calculations?
    for auto baud a common technique is to hit an odd numbered character (eg: 'A' = 0x41) and measure the start bit width with a loop by polling RIN status bit of the 9902


    EDIT:
    if you are having problems with the 9995 keeping up with the terminal program sending it data then try setting the terminal program to transmit 2 stop bits to give it more of a chance, failing that use interrupts on the 9902 and/or re purpose the RTS line to hold off the PC
    Last edited by Tony Rowell; January 2nd, 2014 at 05:08 PM.

  2. #602

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    The board may be moderating newcomer posts, but I just found the last message you sent to my personal e-mail today, Jim--three weeks after you sent it (it was there all along, I just missed it somehow). I'll get an answer out to you shortly!

    One note on TMS9900 FPGA cores: the F18A VGA replacement (from Matthew Hagerty of CodeHackCreate) for the TMS9918A has a fully functional TMS9900 core incorporated into it, designed to work as a system coprocessor.

  3. #603
    Join Date
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    Quote Originally Posted by Tony Rowell View Post
    what is the issue with baud rate calculations?
    for auto baud a common technique is to hit an odd numbered character (eg: 'A' = 0x41) and measure the start bit width with a loop by polling RIN status bit of the 9902
    Yes, this is the technique used by the code on my TMS9995 breadboard system. You then look up the loop count in a table to get the value to load into the 9902 data rate registers for the matching baud rate. So actually if you're changing from a 1 wait state system to a no wait state system, the loop count values will change, although the values to load into the 9902 will not, as they are based on the clock frequency which is not changing. So you could just tweak the code to load the value for the 9902 for the baud rate you want to use directly, rather than looking it up in a table.

  4. #604
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    Quote Originally Posted by pnr View Post

    - connecting READY to /RESET should eliminate the automatic wait state. Has anybody done the recalculation work for the baud rate table?

    Paul
    My take on this is that Paul is asking for new baud rate values for the TMS9902 once the TMS9995 is running without wait-states? Surely since the system clock frequency doesn't change, the values for the 9902 remain the same?

    Dave.

  5. #605

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    Quote Originally Posted by tms9995 View Post
    My take on this is that Paul is asking for new baud rate values for the TMS9902 once the TMS9995 is running without wait-states? Surely since the system clock frequency doesn't change, the values for the 9902 remain the same?

    Dave.
    you should be able to just ratio the count. Take the loop timing the start bit and using the 9995 data sheet write down the number of clock cycles and memory accesses for each line of code (it is only a 3 instruction loop). Do this for both with and without wait states, the ration between the 2 cycle counts gives you the scaling factor for the baud rate

  6. #606

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    Quote Originally Posted by Ksarul View Post
    The board may be moderating newcomer posts, but I just found the last message you sent to my personal e-mail today, Jim--three weeks after you sent it (it was there all along, I just missed it somehow). I'll get an answer out to you shortly!

    One note on TMS9900 FPGA cores: the F18A VGA replacement (from Matthew Hagerty of CodeHackCreate) for the TMS9918A has a fully functional TMS9900 core incorporated into it, designed to work as a system coprocessor.
    can you point me to a reference to the 9900 core in the FPGA, I've had a look at the F18A pages and I cant see any mention of it but I'm probably just being blind.

  7. #607
    Join Date
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    Quote Originally Posted by Tony Rowell View Post
    you should be able to just ratio the count. Take the loop timing the start bit and using the 9995 data sheet write down the number of clock cycles and memory accesses for each line of code (it is only a 3 instruction loop). Do this for both with and without wait states, the ration between the 2 cycle counts gives you the scaling factor for the baud rate
    I have to agree with Dave, if you are using the TMS9902 for the serial comms then any wait states (or not) for the main memory should have no affect on the comms.
    The baud rates are defined by the clock feed to the TM9902 and it's register settings.

    Jim

  8. #608
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    Quote Originally Posted by Tony Rowell View Post
    can you point me to a reference to the 9900 core in the FPGA, I've had a look at the F18A pages and I cant see any mention of it but I'm probably just being blind.
    The details on the F18A are rather scattered around.
    There quite a bit mentioned in the thread here.
    http://atariage.com/forums/topic/207...and-resources/

    I've one in my Cortex and it does work well.

    Jim

  9. #609

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    Here's the reference to the 9900 on the F18A page:

    http://codehackcreate.com/archives/335

    It is the second listed feature.

    Guillaume Tello makes extensive use of it with his MLC Compiler.

  10. #610

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    Quote Originally Posted by Ksarul View Post
    Here's the reference to the 9900 on the F18A page:

    http://codehackcreate.com/archives/335

    It is the second listed feature.

    Guillaume Tello makes extensive use of it with his MLC Compiler.
    Thanks, I'd missed that




    Quote Originally Posted by Jim Hearne View Post
    I have to agree with Dave, if you are using the TMS9902 for the serial comms then any wait states (or not) for the main memory should have no affect on the comms.
    The baud rates are defined by the clock feed to the TM9902 and it's register settings.
    Jim
    that is true but ...

    if you are doing auto baud using a software loop to measure the width of the start bit you do need to take it into count. For example, if removing the wait states makes the timing loop take half the time it does with wait states then the same start bit will take twice the number of loops which would make it appear that the serial port is half the baud rate it really is.

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