I want to write a TA which will be called from the Normal World and be handled by a specific Trusted OS. Currently, I am using 3 Cactus OS (provided by TF-A-Tests) in SEL1, and a Hafnium in SEL2. Here is my partial building cmd

make CROSS_COMPILE=aarch64-none-elf- SPD=spmd CTX_INCLUDE_EL2_REGS=1 ARM_ARCH_MINOR=4 PLAT=fvp DEBUG=1 BL33=../tf-a-tests/build/fvp/debug/tftf.bin BL32=../hafnium/out/reference/secure_aem_v8a_fvp_clang/hafnium.bin SP_LAYOUT_FILE=../tf-a-tests/build/fvp/debug/sp_layout.json all fip

I have created some EL3 services at services/std_svc, but have not created a TA. 

In my view, to call the TA, I think I should pass (1) the ID of the TA (but I am not sure how to get the ID) (2) several parameters, which may be loaded into registers. Here may be a calling process.

ldr x0,=0xdeadbeef // loading ID

ldr x1,=0x11111 // input parameters

ldr x2,=0x22222 // input parameters

smc #0

Then I think I should write a corresponding handler (of the TA) in Cactus OS. When we call "smc #0", EL3 will trap it, and route it to a specific TA.

However, I don't know how to do it. Can you provide some useful examples?

Sincerely,

Wang Chenxu