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what is the difference between the device memory and the strongly-order memory ?

Note: This was originally posted on 21st June 2011 at http://forums.arm.com

Dear All,

       Both device and strongly-order memory are used to model memory-mapped peripherals and I/O locations in ARMv7 architecture. And the architecture specification says that both device and strongly-order memory should conform the following two rules:
       a).   all accesses occur at their program size.

.   the number of accesses is the number specified by the program.

       My question is what is the difference between the device memory and the strongly-order memory ? Does the access sequence of strongly-order memory should strictly conform the program order while the access sequence of device memory can be different to the program order?

      Can anyone give me some explanation? Thanks.

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0 Dong Luo over 12 years ago

Note: This was originally posted on 21st June 2011 at http://forums.arm.com

Hi isogen74,

Thans for your reply. So, the order of accesses to the device memory should conform to the program order, am I right?

A write to Strongly-ordered memory is only considered complete when the transaction is acknowledged as complete by the memory or peripheral device.

A write to Device memory is permitted to complete (from the processor's point of view) before it actually reaches the peripheral or memory device. Device memory is therefore faster for typical uses.
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0 Peter Harris over 12 years ago

Note: This was originally posted on 21st June 2011 at http://forums.arm.com

A write to Strongly-ordered memory is only considered complete when the transaction is acknowledged as complete by the memory or peripheral device.

A write to Device memory is permitted to complete (from the processor's point of view) before it actually reaches the peripheral or memory device. Device memory is therefore faster for typical uses.
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0 Peter Harris over 12 years ago

Note: This was originally posted on 21st June 2011 at http://forums.arm.com

[color=#222222][size=2]> So, the order of accesses to the device memory should conform to the program order, am I right? [/size][/color]
Yes.
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0 mars over 11 years ago in reply to Peter Harris

device memory might not be in order if two access are written/read to/from different slaves.
please check: cortex-a device memory access order limited in some range?
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