path: root/docs/porting-guide.md
diff options
authorSandrine Bailleux <sandrine.bailleux@arm.com>2014-03-31 11:25:18 +0100
committerSandrine Bailleux <sandrine.bailleux@arm.com>2014-04-08 15:22:56 +0100
commit9e86490f8f14f25c7583aaf37412114219f3eb8e (patch)
tree97f364c0c7d33077fccaa737b806617bc9fc491b /docs/porting-guide.md
parent65a9c0e96a9fe033936f40b7603e0ae267b97d96 (diff)
Define frequency of system counter in platform code
BL3-1 architecture setup code programs the system counter frequency into the CNTFRQ_EL0 register. This frequency is defined by the platform, though. This patch introduces a new platform hook that the architecture setup code can call to retrieve this information. In the ARM FVP port, this returns the first entry of the frequency modes table from the memory mapped generic timer. All system counter setup code has been removed from BL1 as some platforms may not have initialized the system counters at this stage. The platform specific settings done exclusively in BL1 have been moved to BL3-1. In the ARM FVP port, this consists in enabling and initializing the System level generic timer. Also, the frequency change request in the counter control register has been set to 0 to make it explicit it's using the base frequency. The CNTCR_FCREQ() macro has been fixed in this context to give an entry number rather than a bitmask. In future, when support for firmware update is implemented, there is a case where BL1 platform specific code will need to program the counter frequency. This should be implemented at that time. This patch also updates the relevant documentation. It properly fixes ARM-software/tf-issues#24 Change-Id: If95639b279f75d66ac0576c48a6614b5ccb0e84b
Diffstat (limited to 'docs/porting-guide.md')
1 files changed, 8 insertions, 3 deletions
diff --git a/docs/porting-guide.md b/docs/porting-guide.md
index 56467fb..5dca6fd 100644
--- a/docs/porting-guide.md
+++ b/docs/porting-guide.md
@@ -208,6 +208,13 @@ the implementer chooses. In the ARM FVP port, they are implemented in
platform) & `platform_get_stack()` (to return the base address of that
stack) (see [../plat/common/aarch64/platform_helpers.S]).
+* **Function : uint64_t plat_get_syscnt_freq(void)**
+ This function is used by the architecture setup code to retrieve the
+ counter frequency for the CPU's generic timer. This value will be
+ programmed into the `CNTFRQ_EL0` register.
+ In the ARM FVP port, it returns the base frequency of the system counter,
+ which is retrieved from the first entry in the frequency modes table.
2.2 Common optional modifications
@@ -446,9 +453,6 @@ This function executes with the MMU and data caches enabled. It is responsible
for performing any remaining platform-specific setup that can occur after the
MMU and data cache have been enabled.
-In the ARM FVP port, it zeros out the ZI section and enables the system level
-implementation of the generic timer counter.
This function is also responsible for initializing the storage abstraction layer
which is used to load further bootloader images.
@@ -771,6 +775,7 @@ BL3-1 runtime services and normal world software can function correctly.
The ARM FVP port does the following:
* Initializes the generic interrupt controller.
* Configures the CLCD controller.
+* Enables system-level implementation of the generic timer counter.
* Grants access to the system counter timer module
* Initializes the FVP power controller device
* Detects the system topology.