Can a normal C variable be mapped to a register?

Heinrich Schwarz

Hello,

When reviewing some C code (edma3_lld_02_11_05_02/examples/CSL2_DAT_DEMO/src/dat_edma3LLD/csl2_dat.c), I found the following piece of code, which quite confuses me:

//Defined as global variables
static volatile Uint32 TransferCompleteH = 0x0;
static volatile Uint32 TransferCompleteL = 0x0
void someFunct() {
/* Set a 1 bit in the TransferComplete register corresponding to the tcc */
SET_REGISTER32_BIT(TransferCompleteL,tccNum);
}

What confuses me: The comment mentions a "register". Is the variable TransferCompleteH/Lsomehow mapped to a "real" hardware register?
Or is just the comment a bit imprecise?

Thx

over 13 years ago

0 Chad Courtney over 13 years ago

TI__Mastermind 30825 points

The function SET_REGISTER32_BIT typically would be used with Memory Mapped Registers (MMR.) To read the register at the memory location and set indicated bits and write back to the memory location where the MMR resides.

Best Regards,

Chad

0 Heinrich Schwarz over 13 years ago in reply to Chad Courtney

Intellectual 450 points

Hello Mr Courtney,

Thanks for answering my question. How can I find out, wether an register is memory mapped?
Is this the case with the source above, or is just the comment misleading?

Thx

0 Chad Courtney over 13 years ago in reply to Heinrich Schwarz

TI__Mastermind 30825 points

Most registers are MMRs. If you find it in the Data Manual or the IP's UG, with an address (or offset address) associated with it then it's a MMR.

The registers that aren't MMRs would be the General Purpose registers: A0-A31, B0-B31, CSR, EFR, ... These are all tied to the CorePac's themselves.

Best Regards,

Chad

0 Heinrich Schwarz over 13 years ago in reply to Chad Courtney

Intellectual 450 points

Hello,

So it seems the variables are just ordinary L2 memory.

Thanks!

0 Chad Courtney over 13 years ago in reply to Heinrich Schwarz

TI__Mastermind 30825 points

Technically, variables are going to be whatever you declared them to be.

We were really talking about Registers, which a Variable may or may not point to a specific memory mapped register, depending on if it is declared to be such.

Best Regards,

Chad

0 Heinrich Schwarz over 12 years ago in reply to Chad Courtney

Intellectual 450 points

Hi Chad,

Thanks for the clarification. As it turned out, the author of the DAT driver just used the macros to emulate bitfields in ordinary memory.
It was just the slightly misleading wording of the comment that confused me.

Thx

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Can a normal C variable be mapped to a register?