TMS320F28377D: Why do the IPC drivers perform read-modify-writes on read-zero registers?

IainRist

Why do the IPC drivers perform read-modify-writes on read-zero registers?

The Technical Reference Manual spruhm8h states that the IPCACK, IPCSET and IPCCLR registers all read as zero. In the following files those registers are written through a read-modify-write operation. Is the code performing a superfluous read or am I missing something?

File name	Number of RMW operations
F2837xD_Ipc_Driver.c	7
F2837xD_Ipc_Driver_Util.c	3
F2837xD_Ipc_Driver_Lite.c	31

over 6 years ago

0 Christopher Chiarella over 6 years ago

TI__Mastermind 30255 points

Hello

Yes, the compiler is likely translating the OR operations into a RMW. The compiler wouldn't know that the register is a read-zero.

Best regards

Chris

0 IainRist over 6 years ago in reply to Christopher Chiarella

Intellectual 711 points

Hi Chris,

So why is the F2837xD-specific code, where the target registers are known to be read-zero, performing RMW (reg |= value) rather than direct writes (reg = value)?

Thanks,

Iain

0 Christopher Chiarella over 6 years ago in reply to IainRist

TI__Mastermind 30255 points

Iain

The compiler isn't specific to F2837x, it covers all C2000 devices so as far as I'm aware it will always do the RMW. You can try adjusting optimization to >= OP2 and see if that changes the behavior, I don't think it will thought.

Best regards

Chris

0 IainRist over 6 years ago in reply to Christopher Chiarella

Intellectual 711 points

Hi Chris,

My issue isn't with the compiler. That is doing exactly what I would expect it to do. My issue is that the source code shouldn't be performing RMW on a chip-specific register that is read-zero in the first place.

I understand the same IPC library interface is probably used across multiple chips, but I am highlighting the F28377D-specific implementation of that interface does not need to perform the RMW of the registers that are read-zero on the F28377D as it just wastes cycles.

Is the IPC library source code shared across multiple devices that have different read-write properties?

Thanks,

Iain

0 Christopher Chiarella over 6 years ago in reply to IainRist

TI__Mastermind 30255 points

Iain

Oh ok, I understand. This source code is specific to this device.

I will file this with the driver owners to make this optimization in a future revision.

Thanks

Chris

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TMS320F28377D: Why do the IPC drivers perform read-modify-writes on read-zero registers?