helper_fullwr will call memory_write if it does not go to [0x0000 - 0x0100) range otherwise it will call cpu_outb because this range has a dual access through ST and OUT instructions
On Wed, Jul 6, 2016 at 12:52 PM, Peter Maydell <peter.mayd...@linaro.org> wrote: > On 6 July 2016 at 10:36, Michael Rolnik <mrol...@gmail.com> wrote: > > Peter, > > > > I think I will do the following > > 1. helper fullwr will modify CPU owned registers by itself and call > cpu_outb > > for non owned registers > > This doesn't sound right -- if helper_fullwr is for memory writes > it shouldn't call cpu_outb, which is IO space. > > The distinction here is between different kinds of what QEMU > calls "address spaces".Pretty much every CPU has an address > space for "memory", which is what you can access via the usual > load and store instructions. Some CPUs also have an address > space for "IO", if they have dedicated different IO instructions. > The usual example of this is x86 -- an X86 "outb" instruction to > port 0 is different from store-byte to memory address 0. So > we have an address space for the "io space" which inb/outb/etc > access, and one for memory which loads and stores access. > Most CPUs don't have this kind of split idea of device IO > as different from memory access (their devices are "memory > mapped"); our models of these CPUs don't have an address > space for IO, because there isn't one in the real hardware. > > It looked to me from glancing through the data sheet that these > IO registers in your CPU are accessed via normal memory loads > and stores, which would mean that the devices for them should > go in the usual address space for memory, not a different > one for IO, and you shouldn't call cpu_outb at all. > > thanks > -- PMM > -- Best Regards, Michael Rolnik
