Electronic – Splicing Buses in Kicad

kicadpcb-design

I would like to be able to splice two buses in kicad into a third larger bus.

Say I have a subsheet with an output pin connected to a 16 wire bus (an unrelated note, it took me a while to figure out how to get buses through a subsheet but it works). I have another sheet where I place several identical copies of that subsheet and want to have the output of that sheet be a N*16 bit bus to be used in the top-level sheet, as an illustration, here is a simplified example of what I want to achieve

enter image description here

The first bus passes through perfectly, (e.g. lines 1-16 have associated nets and are properly placed in pcbnew), however the second bus (lines 17-32) doesn't get connected

I figured out a way around this by assigning each subcomponent bus a seperate unique bus name and then mapping each one, pin by pin to the corresponding pin on the master bus. it is however rather inconvenient given that the full schematic has 512 total lines in the bus ( :O ).

The not-so-convenient-solution is illustrated below (not all pin-assignments are shown for clarity)

enter image description here

In short, the question is if there is a way to get around bit-banging all the buses together like this and have a solution more like the first non-working method.

EDIT

Before anyone asks, this doesn't work either

enter image description here

Best Answer

For splicing buses the key point to remember is that the name is ignored and the connection is carried out solely on the basis of the line ID. To illustrate this I have spliced 3 buses in the example below: ETH_RGMII, USB_ULPI, and UART into a single bus COMM by connecting labels as follows.

ETH_RGMII[0..14] → COMM[0..14]

USB_ULPI[15..27] → COMM[15..27]

UART[28..31] → COMM[28..31]

Connection Example #1

As a result of this restriction if one were to change the indices on UART to [0..3] then no connections would be made due to the lack of matching indices on the "UART[0..3] → COMM[28..31]" connection.

One can take advantage of this to make splicing more flexible by incrementing the starting indices of the individual buses to be spliced by 100 (spaced indexing) so that one can flexibly resize the individual channels without having to worry about unintended connections.

In this scenario the 3 channels are now connected with as follows:

ETH_RGMII[0..14] → COMM[0..99]

USB_ULPI[100..112] → COMM[100..199]

UART[200..203] → COMM[200..299]

If I were now to expand the USB_ULPI bus by a few lines this eliminate the need to re-index UART.

Connection Example 2 with spaced indexing

Related Topic