el3_payload/README

EL3 test payload
================

This program is a very simple EL3 baremetal application. It has been developed
to test the ability of the Trusted Firmware-A to load an EL3 payload. All it
does is making sure that all CPUs enter this image and if so, reports it through
the UART.


Building
--------

$ make PLAT=juno
or
$ make PLAT=fvp


Preparing Juno board configuration files
----------------------------------------

You should have the following line in your 'SITE1/HBI0262X/board.txt' Juno
configuration file on the SD card (where X depends on the revision of your Juno
board):

  SCC: 0x0F4 0x000003F8

This:
 - ensures all CPUs are powered on at reset;
 - designates the Cortex-A53 #0 as the primary CPU.

See the 'Assumptions' section below' for more details.


Running on Juno
---------------

The Trusted Firmware-A must be compiled with SPIN_ON_BL1_EXIT=1. This will
introduce an infinite loop in BL1 that gives you some time to load and run the
EL3 payload over JTAG.

Boot the board and wait until you see the following messages on the UART.
(Note that the "INFO" messages appear only in a debug build of the Trusted
Firmware but you should see the "NOTICE" messages in any case.)

  NOTICE:  BL1: Booting BL31
  INFO:    BL1: BL31 address = 0x80000000
  INFO:    BL1: BL31 spsr = 0x3cd
  INFO:    BL1: BL31 params address = 0x0
  INFO:    BL1: BL31 plat params address = 0xf1e2d3c4b5a6978
  INFO:    BL1: BL31 address = 0x80000000
  INFO:    BL1: BL31 spsr = 0x3cd
  INFO:    BL1: BL31 params address = 0x0
  INFO:    BL1: BL31 plat params address = 0xf1e2d3c4b5a6978
  NOTICE:  BL1: Debug loop, spinning forever
  NOTICE:  BL1: Please connect the debugger to jump over it

TODO: Update the above messages.

At this point, type the following command in a shell from the EL3 test payload
top directory:

$ make PLAT=juno run

You should see something like this in your shell (it takes a few seconds):

  Trying to detect your DSTREAM unit...
  Available connections:
    USB:000765
  Connecting to USB:000765...
  Connected to running target Cortex-A53_0
  Execution stopped in EL3h mode at EL3:0x000000000BEC2548
  EL3:0x000000000BEC2548   B        {pc} ; 0xbec2548
  Loaded section ro: EL3:0x0000000080000000 ~ EL3:0x0000000080000123 (size 0x124)
  Loaded section .data: EL3:0x0000000080000128 ~ EL3:0x0000000080000197 (size 0x70)
  Entry point EL3:0x0000000080000000
  Disconnected from running target Cortex-A53_0

And on the Juno UART, this should print the following messages:

  Booting the EL3 test payload
  All CPUs booted!


Running on FVP (AEMv8A)
-----------------------

First, copy the "bl1.bin" and "fip.bin" files into the current directory.
Alternatively, symbolic links might be created.

Then run:

$ make PLAT=fvp run

Note: The EL3 payload does not work on the Foundation FVP.
(This is because it expects 8 CPUs and the Foundation FVP has maximum 4.)


How does it work?
-----------------

There is a per-cpu array. Each entry is initialised to a "dead" value.  On entry
into the payload, each CPU writes its MPID to its entry, which allows it to
signal its presence.

Secondary CPUs then spin forever.

The primary CPU carries on.
  1) It prints a "welcome" string.
  2) It waits for each entry in the CPUs array to be updated.
  3) Once all CPUs have been detected in that way, it prints a success message.
  4) Finally, it spins forever.


Assumptions
-----------

- All CPUs enter the EL3 test payload at some point.
  The order doesn't matter, though.
  If some CPU doesn't boot then the EL3 payload will wait forever.

- On FVP, the number of cores is hard-coded to 8.
  If the FVP model is configured to disable some CPUs then the EL3 payload will
  hang, waiting forever for absent CPUs.
  For the same reason, the EL3 payload hangs on the Foundation FVP (which has
  4 CPUs only).

- The UART is already configured.

- On Juno, the primary CPU is hard-coded to the Cortex-A53 #0.
  Any CPU could be the primary CPU, though. However, the DS-5 scripts launched
  by 'make run' assumes the Cortex-A53 #0 is the primary CPU.

  On FVP, the primary CPU is hard-coded to the CPU with MPID 0x0.

  Designating a CPU as the primary one simplifies the code, More particularly,
  only the primary CPU accesses the UART, which removes the need for
  synchronisation locks to avoid interleaved messages.

- The EL3 test pyaload runs from RAM.
  It can't execute from flash, as we would need to relocate the .data section
  in RAM at run-time and this is not implemented for now.