[Feature request]: Support more boards

[Peter-van-Tol]

Initial Checks

• I have searched Google & GitHub for similar requests and couldn't find anything
• I have read the documentation and couldn't find anything

Description

Add support for Tang Nano 20K and the HAT for the Raspberry Pi.

Documentation: https://wiki.sipeed.com/hardware/en/tang/tang-nano-20k/nano-20k.html

Affected Components

• CLI.
• Supported boards (i.e. 5A-75B, 5A-75E, HUB75HAT, etc.)
• Supported connections (i.e. SPI, Ethernet, etc.)
• Modules (i.e. GPIO, PWM, stepgen, encoders, etc.)
• Documentation

[Peter-van-Tol]

The firmware works.

However flashing the firmware requires a Windows PC with Gowin Programmer installed until this issue has been resolved:
trabucayre/openFPGALoader#511

[Peter-van-Tol]

Unfortunately SPI does not work with 3-wires on a RPi. Going to implement a 2-wire connection using I2C

[Peter-van-Tol]

Widened the scope of this feature request to include the following FPGA's:

• Colorlight 5a-75b (already supported)
• Colorlight 5a-75e (already supported)
• Colorlight i5;
• Colorlight i9;
• Linsn RV901T (partially supported);
• Sipeed TangNano20K.

This feature request also separates the FPGA from the extension board (such as the HUB75HAT, Tang20KHAT, but also the 'default' extension boards from AliExpress for the Colorlight i5 and i9. The FPGA's are defined with their original pinout, i.e. for the Colorlight i5 this is the DIMM slot. The translation to the pinout of the extension board is done with a separate class, which can be easily created (no in-depth knowledge of Python required).

The change in architecture also requires a change in the JSON-configuration. The board will be defined with a structure which will look like this (currently under development):

"board": {
  "family": "colorlight",
  "type": "5a-75b",
  "revision": "7.0",
  "extension_board": "HUB75HAT",
  "connection": {
    "connection_type": "spi",
    "mosi": "spi:0",
    "miso": "spi:1",
    "clock": "spi:2",
    "cs_n": "spi:3",
  }
} 

Remarks with this structure:

1. Families supported after this change are colorlight, linsn, and sipeed.
2. All families have the properties type, extension_board, and connection. The property revision only exists on families which have multiple versions of the board with different pin-outs. Currently this is only the colorlight family.
3. The property connection has been moved to the board definition. Reason for this is that not all boards support all connection types, for example the sipeed family currently does not have a member support Ethernet.

This new setup allows for easy addition of boards to this project. Rule of thumb is a new board to an existing family takes roughly one hour. Creating a new family costs an additional one hour to implement and test.

[Peter-van-Tol]

Unfortunately SPI does not work with 3-wires on a RPi. Going to implement a 2-wire connection using I2C

Update:
The driver and firmware have been modified to work with a 'poor man's' three wire SPI. This is a 4-wire SPI, but the CS_n signal has been dropped in favor of a sync-byte. Preliminary testing shows no degradation of performance in both firmware and driver.

Considerations:

• currently only works with the spidev driver;
• in the connection-string a flag NO_CS can be given to indicate that a sync-byte has to be added in the communication frames. In future (when SPI_3WIRE is supported on the RPi5), the number of flags can be extended. Also, when devices require different phase or polarity, this can be handled with flags. An example of loading the driver in the HAL is: loadrt litexcnc connections="spidev:/dev/spidev0.0:NO_CS". With future flags this will be expanded using the |-operator.
• The rationale is that the SPI bus would be exclusive for the firmware anyways to keep things real-time. Dropping the CS-line only affects the timing in the firmware itself