Smart autorouting tool capable of optimal net connection.

Jul 22, 2005 1 Replies

When designing a system (computer) with a 32-bit data bus that is connected to 4 SRAM chips in parallel, each 8-bit wide, the usual (but not optimal) approach would be to connect pin D0 from SRAM chip 0 to processor's D0, D1 from SRAM chip 0 to processor's D1 and so on. However, if we allow the data lines to be interchanged when connecting to the memory chips possibly we could end with a more optimized board layout. Hence I would like to have a schematic/PCB tool were we can specify that each line from the data bus should be connected to a single data pin in the memory bank, but without specifying the connection order. The exact connection between the memory bank data pins and system data lines would be defined only after routing the board. A possible way to specify this in a schematic editor could be as shown in the following pictures (available in .bmp, .png and .jpg file formats):

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In this picture, U1 is the processor, U2 to U5 are SRAM chips, and BW1 specifies how the processor data bus D[31:0] connects to the SRAM chips (Here represented by the MD[31:0] bus, where MD31 is the U2/D7 pin, MD30 is the U2/D6 pin, ..., MD0 is the U5/D0 pin.). BW1 doesn't exist as a component in the board layout, it is defined by the autorouting tool in such a manner to make the board layout as optimal as possible. For instance, SW1 could be for a certain design: D0 = MD7 D1 = MD8 D2 = MD9 D3 = MD1 D4 = MD2 ... After the routing completes, the autorouting tool should generate a report documenting how the connection between D[31:0] and MD[31:0] has been done in BW1.



Do you know any SCH/PCB layout tool capable of doing this? Also, is there any pitfalls, drawbacks or caveats when interchanging data lines or address lines in SRAM memories in order to archieve an optimal board design?



Best Regards, Márcio.


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> In this picture, U1 is the processor, U2 to U5 are SRAM chips, and > BW1 specifies how the processor data bus D[31:0] connects to the SRAM > chips (Here represented by the MD[31:0] bus, where MD31 is the U2/D7 > pin, MD30 is the U2/D6 pin, ..., MD0 is the U5/D0 pin.). BW1 doesn't > exist as a component in the board layout, it is defined by the > autorouting tool in such a manner to make the board layout as optimal > as possible. For instance, SW1 could be for a certain design: > D0 = MD7 > D1 = MD8 > D2 = MD9 > D3 = MD1 > D4 = MD2 > ... > After the routing completes, the autorouting tool should generate a > report documenting how the connection between D[31:0] and MD[31:0] has > been done in BW1. > > Do you know any SCH/PCB layout tool capable of doing this? Also, is > there any pitfalls, drawbacks or caveats when interchanging data lines > or address lines in SRAM memories in order to archieve an optimal board > design? > > Best Regards, > Márcio.

Hi Márcio

Most pro schematic/ layout tools have a way to make pins swappable, this way you can swap pins on a resistor network or swap gates on a quad or-gate IC.

The only pitfall is that you must ensure that pins only swap within the memory chip and not across chips. For example, if you have three quad and-gate IC's on a board, if the gates are all the same class then the tool can move the gate to another IC. In your case you don't want that to happen.

I have used PCAD, PADS and ORCAD and they all have the capability to do this.

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