ARM versus MIPS GPIO.

[lilzz]

For Pi ARM GPIO is accessed through memory mapped

Code: Select all

 gpio_map = (uint32_t *)mmap( (caddr_t)gpio_mem, BLOCK_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED, mem_fd, GPIO_BASE);
 *(gpio_map+offset) =value

where gpio_map is virtual address. different GPIO is accessed through different offset.

For MIPS the GPIO is accessed through bus address using ioremap function instead of mmap of ARM.
the memory address from ioremap of MIPS cannot be directly derefenced like ARm. It must use readl and writel to access those memory location..


So, the question is why the difference and two different approach between the two. why can't MIPS use mmap or why can't ARM use ioremap?

[gordon@drogon.net]

For Pi ARM GPIO is accessed through memory mapped

Code: Select all

 gpio_map = (uint32_t *)mmap( (caddr_t)gpio_mem, BLOCK_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED, mem_fd, GPIO_BASE);
 *(gpio_map+offset) =value

where gpio_map is virtual address. different GPIO is accessed through different offset.

For MIPS the GPIO is accessed through bus address using ioremap function instead of mmap of ARM.
the memory address from ioremap of MIPS cannot be directly derefenced like ARm. It must use readl and writel to access those memory location..


So, the question is why the difference and two different approach between the two. why can't MIPS use mmap or why can't ARM use ioremap?

ioremap is a Linux kernel call AIUI. mmap works from userland.

Is the MIPS code you're looking at running in the Kernel or a user program?

-Gordon

[lilzz]

ioremap is a Linux kernel call AIUI. mmap works from userland.

Is the MIPS code you're looking at running in the Kernel or a user program?

-Gordon

End goal is I want to use it in the user land.
So, is that means I can adopt the ARM code for the MIPS ?

[dwelch67]

mmap() isnt an arm thing, it is present on mips, arm, x86, and all others. but it really doesnt matter because the peripherals you are punching through the operating system to talk to will vary from one system to another, even from one arm to one arm or one mips to one mips or x86 to x86, as well as ppc to arm or mips vs x86, etc...

Note, this is a bare metal forum...