From 4685b64fc34b3fd23c5d942aeac87fe1ece744e1 Mon Sep 17 00:00:00 2001 From: Louis Mayencourt Date: Fri, 11 Oct 2019 15:27:01 +0100 Subject: [PATCH] DOC: Update ROMLIB page with memory impact info Complete the Library at ROM documentation with information regarding the memory impact of the feature. Change-Id: I5a10620a8e94f123021bb19523a36d558b330deb Signed-off-by: Louis Mayencourt --- docs/components/romlib-design.rst | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/docs/components/romlib-design.rst b/docs/components/romlib-design.rst index d8bc89cea..e0a028e46 100644 --- a/docs/components/romlib-design.rst +++ b/docs/components/romlib-design.rst @@ -111,6 +111,21 @@ The calling sequence for a patched function is as follows: BL image --> function +Memory impact +~~~~~~~~~~~~~ + +Using library at ROM will modify the memory layout of the BL images: +- The ROM library needs a page aligned RAM section to hold the RW data. This + section is defined by the ROMLIB_RW_BASE and ROMLIB_RW_END macros. + On Arm platforms a section of 1 page (0x1000) is allocated at the top of SRAM. + This will have for effect to shift down all the BL images by 1 page. +- Depending on the functions moved to the ROM library, the size of the BL images + will be reduced. + For example: moving MbedTLS function into the ROM library reduces BL1 and + BL2, but not BL31. +- This change in BL images size can be taken into consideration to optimize the + memory layout when defining the BLx_BASE macros. + Build library at ROM ~~~~~~~~~~~~~~~~~~~~~ -- GitLab