This describes requirement of e500 and e500v2 processor to support any debugger. it also provide an insight of switch used and defined.

Signed-off-by: Radu Lazarescu radu.lazarescu@freescale.com Signed-off-by: Prabhakar Kushwaha prabhakar@freescale.com --- Applies on http://git.denx.de/u-boot.git branch master

doc/README.mpc85xx_debugger | 44 +++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 44 insertions(+), 0 deletions(-) create mode 100644 doc/README.mpc85xx_debugger

diff --git a/doc/README.mpc85xx_debugger b/doc/README.mpc85xx_debugger new file mode 100644 index 0000000..b35d710 --- /dev/null +++ b/doc/README.mpc85xx_debugger @@ -0,0 +1,44 @@ +Overview +-------- +Debugger's ability to debug an application is constrained by the +architecture's debug IP / run-control solution that may impose certain +requirements for the application itself. + +Similarly, when referring to the e500 and e500v2 architecture, there are two +basic rules any application has to respect in order to allow full debugging +support: + 1. Keep MSR[DE] bit set + 2. Have a valid opcode that can be fetched from the debug exception + vector [IVPR|IVOR15]. +Where: + MSR : Machine State register + IVPR : Interrupt Vector Prefix Register + IVOR : Interrupt Vector Offset Register + +Depending upon above 2 points there various place in powerpc/mpc85xx/ code +which break the rules: + - MSR[DE] is not se + - Changing the context with a rfi instruction, but omitting to preserve + the [DE] bit in SRR1 + - Changing IVPR/IVOR15 to a new location, before that location is + un-accessible + - Changing IVPR/IVOR15 to a location that does not have a valid opcode + at [IVOR|IVOR15] + - While executing in translated space (AS=1), whenever a debug + exception is generated, the MSR[DS/IS] gets cleared and the processor + tries to fetch an instruction from the debug exception vector + (IVPR|IVOR15); since now we are in AS=0, the application needs to + ensure the proper configuration to have IVOR|IVOR15 accessible from + AS=0 also + +Config Switches: +---------------- +CONFIG_E500_V1_V2 Enables code taking care of above mentioned rule. +CONFIG_DEBUGGER_TEMP_TLB Define temporary TLB number. + It will be used to create temporary TLB for AS0 + during execution in AS1. The TLB entry will be + created for debug exception vector. + Becuase on debug exception MSR[DS/IS] get + cleared i.e. execution space is shifted back + to AS0 and a TLB is required to have debug + exception vecor accessible.