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Are TivaWare Macros for hardware access wrong?

Luis Afonso
Guru 20670 points
Other Parts Discussed in Thread: ENERGIA
//*****************************************************************************
//
// Macros for hardware access, both direct and via the bit-band region.
//
//*****************************************************************************
#define HWREG(x)                                                              \
        (*((volatile uint32_t *)(x)))
#define HWREGH(x)                                                             \
        (*((volatile uint16_t *)(x)))
#define HWREGB(x)                                                             \
        (*((volatile uint8_t *)(x)))
#define HWREGBITW(x, b)                                                       \
        HWREG(((uint32_t)(x) & 0xF0000000) | 0x02000000 |                     \
              (((uint32_t)(x) & 0x000FFFFF) << 5) | ((b) << 2))
#define HWREGBITH(x, b)                                                       \
        HWREGH(((uint32_t)(x) & 0xF0000000) | 0x02000000 |                    \
               (((uint32_t)(x) & 0x000FFFFF) << 5) | ((b) << 2))
#define HWREGBITB(x, b)                                                       \
        HWREGB(((uint32_t)(x) & 0xF0000000) | 0x02000000 |                    \
               (((uint32_t)(x) & 0x000FFFFF) << 5) | ((b) << 2))

//*****************************************************************************

Well, these are the macros.

I only use HWREG personally but i would like to know how the last 3 works, the first 3 i understand fine although i don't understand the usefulness of the 16bit and 8bit access.

Are the last 3 correct? They seem to be the same or am i completely blind?

  • 0
    TI__Guru**** 244400 points

    Hello Luis,,

    I have been using the HWREG, HWREGH and HWREGB for TM4C129 EPI external memory access when I specifically want to be reading a word, half-word or a byte. Turns out to be more useful.

    The other two are useful when setting a flag bit in SRAM and you do not want to waste a whole word for that. Look at the SMBus and SoftI2C examples/drivers.

    Regards

    Amit

  • 0 in reply to Amit Ashara
    Guru 20670 points

    Thank you Amit i will check it out

    So basically yea, i am completely blind. I just say the difference.

    I guess i don't much usefulness of the 16-8bits because i usually use the address macros from TivaWare which are all 32bits.

  • 0 in reply to Amit Ashara
    Guru 117855 points

    Hi Amit,

    Language police arrive...

    Amit Ashara said:
    when setting a flag bit in SRAM and you do not want to waste a whole word

    Might the issue not be so much the, "waste" of a whole word - but instead the potential to wreak havoc by, "painting with too broad a brush?"  By limiting/confining the "size/width" of such operation - the impact is made more surgical - may even free the user from "detailed knowledge" of that entire word's (potential & unwanted) command/control...

    In days past (when 8 bit/legged dinosaurs ruled) Petrei, Roberto, Robert & cb1 (then) really could not "waste" a "whole word!" (doubt that our enfeebled MCUs even possessed such)  Today - w/flash many multiples of our past - off chip memory space - "waste" matters not!  (most of the time) 

    Proposed then (rather than waste) is the potential for "unwanted/unanticipated damaging (side-effects)" - caused by a misplaced bit(s) - when executing a write or register load - "broader" than it really has to be.

    Your take - s'il vous plait...

  • 0 in reply to cb1_mobile
    Guru 20670 points

    i had to program some of the smaller MSP430, i used a abstraction IDE, Energia. Well that didn't go well eheh. Just a code with a pattern for 2 LEDs and a digital interrupt consumed all the flash. 

    So i had to re-learn in 2h direct register programming in the MSP430, there i usually used a whole 16bit word (it's 16bit the processor) but i used operations like |= and &=~.

    Most of the times i would just operate the needed number of bits, for bit 15 i would use a 16bit word, but i can see the way i done i could just use 8bits for everything and shift the data left before doing that |= or &=~ attribution to the registers

  • 0 in reply to cb1_mobile
    TI__Guru**** 244400 points

    Hello cb1,

    Yes it could be. But the reference did come from devices with smaller SRAM and large programs still to be done by a customer.

    Regards

    Amit

  • 0 in reply to Amit Ashara
    Guru 117855 points

    Our readings may differ - poster originally asked only referencing TivaWare.  Then identified TMC129 - and only recently presented MSP - which is not "bounded" by TivaWare - thus disallowed.

    Hard to characterize TM4C129 as possesor of, "smaller SRAM" or "size limited" programs.

    The dangers of, "painting with too broad an MCU brush" are real - and that point has (now) been minimized - we think incorrectly...  "Waste" is secondary to the potential to cause issues - by (needliessly) exposing each/every bit to alteration - when only a proper few should be so targeted!