So, what I need to do, if I understand correctly, is to create a fixed mapping >From a virtual address to a physical address on the tlb, and use this Virtual address to change the values of EntryLo to 0xD in order to Access the device on the address range I mapped Chip-select 1 to? (Excuse my poor phrasing, I've been googling all day...) Any idea on how I might accomplish that from a driver? I've found a function called add_wired_entry(...), is this What I should be using? Thanks! Gilad. -----Original Message----- From: Dominic Sweetman [mailto:dom@xxxxxxxx] Sent: Tuesday, November 30, 2004 12:25 PM To: Gilad Rom Cc: linux-mips@xxxxxxxxxxxxxx Subject: Re: CP0 EntryLo Gilad Rom (gilad@xxxxxxxxx) writes: > I am attempting to access a peripheral device over the Au1500 static bus. > > According to the Au1500 Databook, Whenever I set the Chip Select config > Register DTY bits to 1 (for "I/O Device"). > I must also set Bits 29:26 of CoProcessor 0 to 0xD, to represent > bits 35:32 of the Physical address. "CoProcessor 0" is a kind of fiction represented by a whole bunch of registers, so you've wandered a long way into the weeds here. > My question is, if anyone can answer it, is how do I setup > The CoProcessor0 registers 29:26 in my driver? I think you are referring to the "EntryLo0-1" register pair. These are used as staging registers when reading or writing entries in the TLB, which is the address translation table. The manual is implying is that you need to set up a TLB entry to access these high physical addresses. In Linux most of the TLB is maintained by the kernel as a cache of the translations used by user programs. That's probably why you see "random values" from the staging registers; the kernel is busy taking exceptions when required translations aren't in the TLB and fixing them up. However, the Au1500 hardware permits a small number of TLB entries to be "wired", for fixed functions like your I/O accesses. I'm not enough of an expert on the Linux kernel to tell you how to set up a wired entry: but grep through the sources and you'll turn something up! > I have noticed a set of functions called write/read_c0_entrylo[0,1], > But I keep getting random values when invoking these from my driver. I think those are way too low-level for your purposes. -- Dominic Sweetman MIPS Technologies
