ULP advisor & unused pin termination

1. That drives the pin to a fixed low level. That allows unconnected pins that can be used later by soldering a wire or attach a probe on it if necessary. Tied down pins are lost.

2. Here assembly comes to help - a usual loop is done by counting down in assembly language instead of counting up. When counting down you have only an conditional jump if counter is zero (jnz). When counting up, you must check if upper limit is reached - you need to do a substraction of the counter and the limit and after that follows the conditional jump. Some clock cycles to spare.

3. I would use 16 bit integers as the msp can operate on them directly and with the struct of 28 bits you still need 2 bytes to store the values anyway.

Jan Kesten said:

Tied down pins are lost.

Jan Kesten said:

Some clock cycles to spare.

For 4., I don't exactly know what the question is. Probably why there is no µA/Mhz rating fo the MSPs. If so, the answer is that such a rating is only meaningful for MCUs with a fixed operating frequency.
Current consumption and frequency don't scale linearly. Current consumption consists of two parts. A static current and a dynamic current. While the satic curren tis more or less constant for all operating frequencies, the dynamic current rises with the operating frequency.
Also, the dynamic current depends on teh actualyl executed instrucitons. Instructions that require accessing the flash for instruction, addresses, parameters and maybe values, draw more than those which pull the parameters and values from the constant generator or ram or hardware registers. And if the code is executed from RAM, things are different again. Also, the supply voltage has some influence too. Many other MCUs only have a fixed operating voltage.
So only a few typical values are given for specific combinations/frequencies. Which do not linearly scale with frequency or operating voltage, so a single index value like µA/MHz is impossible to give.

1. So unused pins should be

       a. Set as ouput dircetion

        b.  Set driver to zero

        c. Connected to gnd by external means, is it?

2. Similarly if a single flag bit, is used, char is more sufficient instead of unsigned bit :1 . IS it? DO CCS support bit variable also?

Either set to output direction with low output, or set to input with internal pulldown, or set to input with external pulldown.

Since external pulldown requires routing and maybe even a resistor (a direct GND connection is not a good idea during development, as accidental programming of the pin as high output will cause high currents then), and internal pullups weren't available on the 1x family, a low output and no external connection was the preferred option.

1, As Jan has said, it better to represent & work on unsigned int

struct
{
    unsigned  vol_det : 14;
    unsigned  vol_rel : 14;
}over;

Other method is to use unsigned int. 16 bits.

Which one's more efficient & power saver. :)

2. Similarly,

struct
{
    unsigned  vol_det : 1;
    unsigned  vol_rel : 1;
}over;

Other method is to use unsigned char 8 bits.

Which one's more efficient & power saver. :).

3. Do CCS has bit datatype also?

Hi,

quite simple answer:

1. two unsigned 16bit integers are better, there are instructions to operate on them directly and the same goes for fetching them from memory. Structs are maybe more dense packed, but need unpacking which costs extra cycles (and instructions)

2. not done a compile and disassembly test I would suspect a single unsigned char with appropriate bit instructions will be faster (or the compiler is clever enough since it is a bitfield)

3. Bits are not really useful since the smallest piece of data which can be handled by the cpu is a byte. But you can use bit fields as in 2. 

FYI, I'm going to add a Wiki link that documents ULP advisor rules:

http://processors.wiki.ti.com/index.php/ULP_Advisor 

Hi, I want to know which one would be more efficient:

1. struct
  {
    unsigned  vol : 1;
  }over;

2. Other method is to use unsigned char 8 bits.

unsigned char over_vol;

Which one's more efficient & power saver. :). Which one should I use. 

Hi!

If you need to save power, use unsigned chars, no structs. Structs almost always introduce overhead for managing them but they can save space. I've done a (very) simple test to illustrate this:

1. test1 is a simple program with your single bit struct
2. test2 is a simple program with your single char instead
3. test3 and test4 are the same but have 24 values or 3 structs each

 text data bss dec hex filename
 120 0 0 120 78 test1.elf
 112 0 0 112 70 test2.elf
 696 0 0 696 2b8 test3.elf
 240 0 0 240 f0 test4.elf

Some tip for an another ULP rule.

Internal reference voltage for example at sigma delta A/D  should be switched off, before entering LPM, otherwise current which goes trough is about 180 uA.

Martin Fridrich said:

Internal reference voltage for example at sigma delta A/D  should be switched off, before entering LPM

Especially if the delay between two samples is shorter than the reference settlign time, disabling the reference is completely useless.

Fully agree with: Especially if the delay between two samples is shorter than the reference settlign time, disabling the reference is completely useless.

But ULP at this moment has also another weak rules like started with - Avoid

For example MSP430F20x3 has Iref between 190 -280 uA (by Datasheet). So than could be better to play with on/off reference than with LPM. Lets say with measurement freq. <100Hz for Sigma Delta and for 10 bit AD < 16kHz. ( Tsettle*2)^-1)

ULP is here for less advanced engineers :-) Experts already has enough knowledge about low power technics. For constant current 190 uA (Sigma delta) you need 1,6644 Ah battery tu run reference for 1 year. And MSP430 is here mainly for battery operations. For 10 Bit AD at corresponding familly Iref current without current buffer is 0,25 mA. So for one year operation you need 2,19 Ah battery for one year. If I compare impacts then I see the rule ULP 1.1 Ensure LPM usage could be less important than if detected in code usage of Internall reference - to Create Rule - Ensure switching off refference when possible (in explanation of this rule can be written check the Settle time for reference) 
 

What should we do with unused SD pins? Ground or leave it open? Also is it possible to connect on gauge to several SD input to get better number?

Masood G. Bashiri said:

What should we do with unused SD pins? Ground or leave it open?

If the pins are only SD inputs and nothing else, I think they can be left unconnected. Unless you want to 'use' them as guard pins, to suppress crosstalk or stray antenna effects on their neighbor pins.