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Cortex-M7: Add support for enabled the D-Cache in write only mode.

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SAMV7 Ethernet:  I- and D-Cache are now enabled in the netnsh/ configuration.  D-Cache is enabled in write-though mode.  This mode is necessary because the DMA descriptors are each 8-bytes in size but the D-Cache cache line is 32-bits in size. So it is impossible make coherency for every 8-byte DMA descriptor without write-through.
This commit is contained in:
Gregory Nutt 2015-03-29 14:42:03 -06:00
parent 7a636fdb13
commit 55a7065f07
2 changed files with 15 additions and 20 deletions
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29
configs/samv71-xult/README.txt
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@ -88,28 +88,21 @@ The BASIC nsh configuration is fully function (as desribed below under
So there is still plenty to be done.
6. There is a port of the SAMA5D4-EK Ethernet driver to the SAMV71-XULT.
Some basic functionality is present, but there is at least two,
probably related issues:
This driver appears to be 100% functional with the following caveats:
- There is a compiler optimization problem. At -O2, there is odd
behavior on pings and ARP messages. But the behavior is OK with
optimization disabled. This may or may not be a compiler issue; it
may be a timing issue.
optimization set to -O2. This may or may not be a compiler
optimization issue (it could also be a timing issue or a need
for some additional volatile qualifiers).
Symptoms vary from build to build but usually result in a hang.
- The driver does not work with I- and D-Caches enabled. The behavior
is just as for when compiler optimization is enabled. I have not
yet found in coherency issues so this might also be timing related.
At -O2, many packets can be exchanged but eventually there is a
hardfault, presumably because of a misdirected DMA.
I have no hard evidence, but I believe that the nature of the problem
related to fact that each descriptor in the arrays are 8-bytes each,
but cache operations are performed on 32-byte memory chunks. So it is
impossible to clean or invalidate a single descriptor without also
cleaning or invalidaing adjacent descriptors.
- I- and D-Caches are enabled but the D-Cache must be enabled in
write-trough mode. This is to work around issues with the RX and TX
descriptors with are 8-bytes in size. But the D-Cache cache line size
is 32-bytes. That means that you cannot reload, clean or invalidate a
descriptor without also effecting three neighboring descriptors.
Setting write through mode eliminates the need for cleaning the D-Cache.
If only reloading and invalidating are done, then there is no problem.
7. The USBHS device controller driver (DCD) is complete but non-functional.
At this point, work has stopped because I am stuck. The problem is that

6
configs/samv71-xult/netnsh/defconfig
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@ -122,8 +122,9 @@ CONFIG_ARCH_DPFPU=y
#
CONFIG_ARMV7M_HAVE_ICACHE=y
CONFIG_ARMV7M_HAVE_DCACHE=y
# CONFIG_ARMV7M_ICACHE is not set
# CONFIG_ARMV7M_DCACHE is not set
CONFIG_ARMV7M_ICACHE=y
CONFIG_ARMV7M_DCACHE=y
CONFIG_ARMV7M_DCACHE_WRITETHROUGH=y
CONFIG_ARMV7M_HAVE_ITCM=y
CONFIG_ARMV7M_HAVE_DTCM=y
# CONFIG_ARMV7M_ITCM is not set
@ -572,6 +573,7 @@ CONFIG_ETH0_PHY_KSZ8061=y
# CONFIG_ETH0_PHY_DP83848C is not set
# CONFIG_ETH0_PHY_LAN8720 is not set
# CONFIG_ETH0_PHY_LAN8740 is not set
# CONFIG_ETH0_PHY_LAN8740A is not set
# CONFIG_ETH0_PHY_DM9161 is not set
# CONFIG_PIPES is not set
# CONFIG_PM is not set