SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
Move 32-Bit MSTF Register to Memory
MSTF | Floating-point status register |
mem32 | 32-bit destination memory |
LSW: mmmm mmmm mmmm mmmm
MSW: 0111 0111 0100 addr
Copy the CLA floating-point status register, MSTF, to memory.
[mem32] = MSTF;
This instruction does not modify flags in the MSTF register:
Flag | TF | ZF | NF | LUF | LVF |
---|---|---|---|---|---|
Modified | No | No | No | No | No |
This is a single-cycle instruction.
One of the uses of this instruction is to save off the return PC (RPC) prior to calling a function. The decision to jump to a function is made when the MCCNDD is in the decode2 (D2) phase of the pipeline; the RPC is also updated in this phase. The actual jump occurs 3 cycles later when MCCNDD enters the execution (E) phase. You must save the old RPC before MCCNDD updates in the D2 phase; that is, save MSTF 3 instructions prior to the function call.
The following example illustrates the pipeline flow for the context save (of the flags and RPC) prior to a function call. The first column in the comments shows the pipeline stages for the MMOV32 instruction while the second column pertains to the MCCNDD instruction.
MMOV32 @_temp, MSTF ; D2| |
MNOP ; R1|F1| MCCNDD is fetched
MNOP ; R2|F2|
MNOP ; E |D1|
MCCNDD _bar, UNC ; W |D2| old RPC written to memory,
; | | RPC updated with MPC+1
MNOP ; |R1|
MNOP ; |R2|
MNOP ; |E | execution branches to _bar