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The hardware level cross-over between logic and physics is of exceptional interest to me, and one of the drivers of my personal investigation of computing more
by jpt4 12y ago
The hardware level cross-over between logic and physics is of exceptional interest to me, and one of the drivers of my personal investigation of computing more generally.
It is my current understanding of FPGAs that they allow for reconfigurable logical circuits, but still implement those functions using fixed spatial circuits, primarily by dispatching signals down routing traces as specified by LUTs. These spatial circuits, in particular the routing paths, as the physical underpinnings of an FPGA are non-reconfigurable, and form the proprietary core of the product. I have three question, if anyone could provide insight:
(1) Is the above notion correct, or does the act of burning in a bitstream to an FPGA actually physically reroute traces within and between blocks of logic gates?
(2) The latter option in (1) would presumably still require some sort of supporting hardware, itself non-reconfigurable, and subject to proprietariness correct?
(3) Are there reconfigurable devices that offer complete, self-hosted reconfigurability? By which I mean that an unconfigured device must first be bootstrapped (via an external tool) to contain the bitstream burning auxiliary circuitry, but this framework remains no more fixed than the rest of the device. Furthermore, the bootstrapped circuits can update themselves, by creating second-generation support circuitry elsewhere on the device, which access and alters the first generation configuration.
Thank you in advance.
Edit: (4) Given the answers to (1), are there any devices that have reconfigurable routing traces?
- deleted 12y ago[deleted]
- jpt4 12y agoInteresting, I had not read of passgates and their associated logic before, thank you. By "disable 8 [of 10] passgates", do you mean driving the control input negative, so that both outputs do not conduct? Also, if you might indulge my edited-in fourth question, 'twould be appreciated. Edit: And then the author of an excellent answer deletes himself, how unfortunate.
- jesuslop 12y agoHi, (1) the above thing is the correct one, simplifying the fpga has a flash memory inside to store the bitstream that configures the god given routing resources so the LUTs etc interconnect as in the netlist. (3) I think you can do it with an actual fpga divided in two logical tiles, one reconfigures the other and vice-versa.
- jpt4 12y agoThank you. Given the fixed state of FPGA circuitry, to your knowledge, does any other kind of device have the property described in "Edit: (4)..."?
- mng2 12y agoRe (3), FPGA Partial Reconfiguration has been a standard feature on high-end parts for a long time. However I've heard (never used it myself) that the present implementations are of limited utility. Most applications that can afford a high-end FPGA can afford an auxiliary processor for management duties, so self-reconfiguration remains something of a curiosity.
- jpt4 12y agoThank you. To your knowledge, does any device have the property described in "Edit: (4)..."?
- mng2 12y agoI'm not sure what you mean by 'physically reroute traces'. If you mean, physically move a metal trace across the chip, that's not really possible at this point. One-time programmable devices (GAL and PAL devices that are essentially obsolete, most FPGAs are SRAM based these days) require physical fuses to be blown in order to program functionality. I suppose that's a physical change, but one that's irreversible.