[Libre-soc-dev] [OpenPOWER-HDL-Cores] microwatt booting linux-5.7 under verilator

[Herrenschmidt, Benjamin]

On Mon, 2022-01-31 at 04:19 +0000, lkcl wrote:
> > How do you even read the SYSCON parameter for frequency?
> 
> 
> SYSCON is just a term for a memory-mapped wishbone ROM which contains
> a crude easily-decoded binary form of devicetree.

Talking of which, if we're going to make use if it (we should), we
probably need to ensure it's also ported to microwatt on LiteX. Though
LiteX has another issue in that it puts MMIO elsewhere iirc.

That or we rely 100% on LiteX having a good DT (and thus use a
different platform for it).
> 
> when you read 0xc0001000 (say) its contents tell you the clock speed.
> 
> 
> 
> at 0xc0001008 is the number of UARTs.
> 
> 0xc0001010 contains the UART0 speed or well you can see the real
> contents syscon.vhdl
> 
> 
> 
> it is _real_ basic but contains everything that
> 
> a cold-start BIOS needs to know, such as "do i even have DRAM, do i
> have an SPI Flash i can read a second
> 
> stage bootloader from" etc etc
> 
> 
> 
> https://github.com/antonblanchard/microwatt/blob/master/syscon.vhdl
> 
> 
> 
> Paul said it was always planned to do reading of these params, the
> entries in devicetree are a temporary hack.
> 
> 
> 
> l.
> 
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