zipcpu / wbspi

A collection of SPI related cores

(Wishbone accessible) SPI Cores

This repository will eventually contain some SPI cores with a Wishbone interface.

For now, it only contains a SPI slave with a raw interface. This slave core will send signals, o_frame at the end of a SPI transaction, o_rd when the core wishes to read a byte from the local interface that will then be sent over MISO, and o_wr when it wishes to write a byte to the local interface once it has been read from the MOSI channel. The first byte sent over MISO is always undefined.

This core was really designed to be high speed. By that I mean that the slave can handle any SPI clock relationship to the system clock up to just less than 33% faster than the system clock. A sad consequence of this is that it might be difficult to reply to an incoming data request without losing an additional 8-bits of MISO. So ... make certain this works in your environment before and if you should try to use it.

Feel free to read more information about this core in the documentation of the core itself.

License

The core as written is licensed under GPL. Feel free to contact me if this license is not sufficient for your needs and we can discuss other options.

wbspi's Issues

Verilator is unhappy in `ADR_CKCOUNT` case

❯ verilator --lint-only wbspi.v
%Warning-WIDTHTRUNC: wbspi.v:282:33: Operator ASSIGNDLY expects 11 bits on the Assign RHS, but Assign RHS's VARREF 'ckcount' generates 12 bits.
                                   : ... note: In instance 'wbspi'
  282 |   ADR_CKCOUNT:  o_wb_data[11:1] <= ckcount;
      |                                 ^~
                     ... For warning description see https://verilator.org/warn/WIDTHTRUNC?v=5.024
                     ... Use "/* verilator lint_off WIDTHTRUNC */" and lint_on around source to disable this message.
%Error: Exiting due to 1 warning(s)

spicpu.v, 234 line
the width of ckcount is 12 bits.

spicpu.v, 282 line
only 11 bits are being assigned.

The suggestion:

-		ADR_CKCOUNT:  o_wb_data[11:1] <= ckcount;
+		ADR_CKCOUNT:  o_wb_data[12:1] <= ckcount;