From 7486eb047563e1cd5f0efebe526699e37319bcbc Mon Sep 17 00:00:00 2001 From: Antonio Nino Diaz Date: Wed, 20 Apr 2016 11:55:14 +0100 Subject: [PATCH] Fix documentation of bootwrapper boot on juno The user guide incorrectly claimed that it is possible to load a bootwrapped kernel over JTAG on Juno in the same manner as an EL3 payload. In the EL3 payload boot flow, some of the platform initialisations in BL2 are modified. In particular, the TZC settings are modified to allow unrestricted access to DRAM. This in turn allows the debugger to access the DRAM and therefore to load the image there. In the BL33-preloaded boot flow though, BL2 uses the default TZC programming, which prevent access to most of the DRAM from secure state. When execution reaches the SPIN_ON_BL1_EXIT loop, the MMU is disabled and thus DS-5 presumably issues secure access transactions while trying to load the image, which fails. One way around it is to stop execution at the end of BL2 instead. At this point, the MMU is still enabled and the DRAM is mapped as non-secure memory. Therefore, the debugger is allowed to access this memory in this context and to sucessfully load the bootwrapped kernel in DRAM. The user guide is updated to suggest this alternative method. Co-Authored-By: Sandrine Bailleux Signed-off-by: Dan Handley Change-Id: I537ea1c6d2f96edc06bc3f512e770c748bcabe94 --- docs/user-guide.md | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/docs/user-guide.md b/docs/user-guide.md index a07185d49..aa385dc55 100644 --- a/docs/user-guide.md +++ b/docs/user-guide.md @@ -1034,9 +1034,9 @@ used when compiling the FIP must match the ELF entry point. #### Boot of a preloaded bootwrapped kernel image on Juno The procedure to obtain and compile the boot wrapper is very similar to the case -of the FVP. Once compiled, the `SPIN_ON_BL1_EXIT=1` loading method explained -above in the EL3 payload boot flow section may be used to load the ELF file over -JTAG on Juno. +of the FVP. The execution must be stopped at the end of bl2_main(), and the +loading method explained above in the EL3 payload boot flow section may be used +to load the ELF file over JTAG on Juno. 9. Running the software on FVP