P2D2 - An open hardware reference design for the P2 CPU

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  • jmgjmg Posts: 14,019
    rogloh wrote: »
    On my own P2 board which I have on hold I was able to get RasPi header compatibility with pins mapping over 1:1 to GPIO numbers, but this certainly made the PCB routing somewhat harder...
    I was a bit more pragmatic, because P2 can do anything on any pin, and the main focus is peripherals, I skipped any nominal 1:1 port-pin notation on Pi, and instead focused on
    5V/3v3/GND, and then filled in the gaps with P2 pins. That covers UART/i2c/SPI links, and Powering, which are the main uses I can forsee.

    That makes the board routing a whole lot simpler, and leaves just getting to all 32 io on P2. That also has a simple solution....

    Here, there are 4 pins that can be GND on Pi, or IO pin P2, which still leaves connects to 4 GNDs to Pi boards. End result is a full 32io and Pi compatible :)


  • If there is a reserve list for P2D2s i'd like to put my name down for two
  • Peter JakackiPeter Jakacki Posts: 8,725
    edited 2019-11-10 - 03:34:48
    I'm running my P2D2 with revB silicon at 355MHz continually with the VGA cog and playing music files. With the ambient at 25'C I am measuring 43'C max at the very center of the chip top or bottom and 47'C if I point the gun down the 3mm center hole. This is just the plain Jane double-sided pcb, no heatsinking etc.

    I will do some more tests and append them to this post later.

    5V in @225ma for 355MHz no I/O load (other than LEDs etc) = 1.125W .

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  • I'm running my P2D2 with revB silicon at 355MHz continually with the VGA cog and playing music files. With the ambient at 25'C I am measuring 43'C max at the very center of the chip top or bottom and 47'C if I point the gun down the 3mm center hole. This is just the plain Jane double-sided pcb, no heatsinking etc.

    I will do some more tests and append them to this post later.

    5V in @225ma for 355MHz no I/O load (other than LEDs etc) = 1.125W .

    That would roughly be less than 500mA at 1V8 based on nothing at 3V3 and 80% efficiency. IIRC you have a 1V8 reg following the switcher, so it will be quite a bit less than 500mA tho. I'm interested to know the 1V8 and 3V3 current if you get a chance t measure it. Meanwhile, this is impressive :smiley:
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  • The 1.8V is straight from the switcher whereas the 3.3V rails are split from a dual output LDO which is fed 3.6V from the other half of the switcher. I need to do another run of P2D2 pcbs so I am tweaking the pcb to include test points suitable for pogo pin probing during testing. However the original P2D2 had jumpers for testing these currents but I am content to feed in an external 1.8V if I want to measure the current.

    Tachyon Forth - compact, fast, forthwright and interactive
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    P2 --- The LOT --- TAQOZ INTRO & LINKS --- P2 SHORTFORM DATASHEET --- TAQOZ RELOADED - 64kB binary with room to spare
    P1 --- Latest Tachyon with EASYFILE --- Tachyon Forth News Blog --- More
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