The Monotron Platform

[thejpster]

It would be nice if 'Monotron' was an application you could run on different boards (see #12). @IGBC also wanted to port it to a board with an FPGA based GPU. This is the classic M-N problem.

Bad solution (M*N):

CPU Board A +---+ Expansion Board A
             \ /
              X
             / \
CPU Board B +---+ Expansion Board B

Better solution (M+N):

CPU Board A +                  + Expansion Board A
             \                /
              Common Interface
             /                \
CPU Board B +                  + Expansion Board B

The standard microcontroller interfaces are:

• SPI (MOSI, MISO, CLK + unique chip-select per slave device + unique IRQ per accessory)
  • SD cards
  • Ethernet interfaces
• I²C (SDA, SCL + unique IRQ per accessory)
  • Real-time clocks
  • Sensors (Temperature, Humidity, Pressure, etc)
• UART (unique RX + TX pair per accessory, plus optional unique CTS/RTS pair per accessory)
  • WiFi Modems
  • Bluetooth Modems
  • RS-232 interfaces

We should endeavour to support all of these, as they all have their uses.

There are several interface pinouts in common use:

• Raspberry Pi 'Hats' (https://www.raspberrypi.org/documentation/usage/gpio/)
• MikroElektronika mikroBUS 'Click boards' (https://www.mikroe.com/mikrobus)
• Arduino Uno 'Shields' (https://www.arduino.cc/en/reference/board)
• Texas Instruments Launchpad 'Booster-packs' (http://www.ti.com/design-resources/embedded-development/hardware-kits-boards.html)
• Beagleboard 'Capes' (https://beagleboard.org/capes)
• STM32 Nucleo 'Expansion boards' (https://www.st.com/en/evaluation-tools/stm32-nucleo-expansion-boards.html)
• Adafruit 'FeatherWing' (https://learn.adafruit.com/assets/78438)

By adding another, we are in danger of:

The general idea I think should be:

+-----------------+   +-[VGA]-[USB?]-[PWR]-+
| :  :            |   |                    |
| :  :            |===|B                   |
| :  :            |   |R                   |
|                 |   |I                   |
|                 |   |D                   |
|                 |===|G                   |
|     Clik        |   |E                   |
| Expansion Board |   |     CPU Board      |
+-----------------+   +--------------------+

+-----------------+   +-[VGA]-[USB?]-[PWR]-+
|                 |   |                    |
| ::::::::        |===|B                   |
|                 |   |R                   |
|                 |   |I                   |
|                 |   |D                   |
|                 |===|G                   |
|     Pi Hat      |   |E                   |
| Expansion Board |   |     CPU Board      |
+-----------------+   +--------------------+

+-----------------+   +-[VGA]-[USB?]-[PWR]-+
|                 |   |                    |
| ::  ::  ::  ::  |===|B                   |
| ::  ::  ::  ::  |   |R                   |
| ::  ::  ::  ::  |   |I                   |
|                 |   |D                   |
|                 |===|G                   |
| Monotron 4-way  |   |E                   |
| Expansion Board |   |     CPU Board      |
+-----------------+   +--------------------+

i.e. a bunch of M CPU boards, designed for Nucleo-64, Launchpad, TinyFPGA, etc, and a bunch of N expansion boards, offering one or more connectors of a specific type.

They interconnect using our own standard 'Bridge' interface, that carries as many signals as we can reasonably consider.

[thejpster]

The MBI (Monotron Bridge Interface) will look something like:

• UART[0..3] RX
• UART[0..3] TX
• UART[0..3] RTS
• UART[0..3] CTS
• (16 pins)
• SPI MISO
• SPI MOSI
• SPI CLK
• SPI CS[0..3]
• (7 pins)
• I²C SCL
• I²C SDA
• (2 pins)
• IRQ[0..3]
• (4 pins)
• GPIO[0..15]
• (16 pins)
• 2x5V (VBUS)
• 2x3.3V (rated at maybe 250 mA?)
• (4 pins)
• Lots of GND

49 pins plus, ground, so say, 64 pins? On a 2x32 header? You'd have a basic sub-set that all CPU boards must implement (I²C, one IRQ, one UART, one SPI CS, etc) which allows for one slot. A fully-featured CPU board could handle four slots, with each slot using all three buses.

[thejpster]

See GitHub.com/neotron-compute