TM4C123GH6PM: GPIODATA offset

Greetings,

Muhammad Inam Ul Haq said:

Why do we have to use an offset of 0x3FC? 

You are correct in noting that such is (not) directly explained w/in the MCU Manual.   Instead the "0x3FC offset" is said to provide increased software efficiency - especially w/in "Read-Modify-Write" implementations.

It is possible to "Search" the MCU Manual - while targeting "0x3FC" for you my small team found (only) 2 "Hits" (on page 601) - neither too enlightening...   You (may) wish to review the MCU Manual's description of "Bit-Banding" - for further detail...

Digging deeper - this was discovered:

Yet - good as this is - the (calculation) of "0x3FC" remains illusive...

Now note those key bits [9:2] (in highlight) - which serve to mask the address bus.   When we "Add the bit-based value of each bit" (again bits [9:2]) your "mystery" 0x3FC (1020 decimal) reveals!

And - the highly capable "API" almost always, "Manages such low-level detail" for you!    (Freeing users from such "exhaustive" detail ... unless they 'really' want it...)   "GPIO.C() code follows:"

void
GPIOPinWrite(uint32_t ui32Port, uint8_t ui8Pins, uint8_t ui8Val)
{
//
// Check the arguments.
//
ASSERT(_GPIOBaseValid(ui32Port));

// Write the pins.
//
HWREG(ui32Port + (GPIO_O_DATA + (ui8Pins << 2))) = ui8Val;    // (255 << 2 = 1020 (0x3FC)  
}

While it's good that you are, "Recognizing & attending to (fine) detail" - in the scheme of things this is a (relatively) minor point.   And there are (many) such "interesting" - yet "Non-Vital" points - which (may) negatively impact your learning!

Instead my young tech team finds:

• Study of the PDL User Guide (an absolutely terrific/helpful resource)
• Review of the (many) programming examples - thoughtfully grouped via "peripherals"
• You may also review the API's "Source Code" (in which the GPIO control mechanisms are revealed! - under "Examples\Peripherals\")
• Obtain the excellent "LPad(s)" - and "Actually: Write, Debug, & Observe" just how the running code behaves.   An (almost) unmatched learning tool!
• Study of the MCU Manual's Peripheral Chapters (those which most appeal)

proves (both) a more efficient & productive method (i.e. a more unified means) to gain understanding & competence - and (in time) "mastery" of these ARM MCUs.     Happy studies...