Dear RFID experts, I’m an Italian student working on TRF7960EVM for the thesis job.I hope someone of you knows about this...

I’m analyzing the “TRF7960 Firmware Source Code” ( released on 23 Feb 2009 ) that I’ve found on the site :
[focus.ti.com]

I can’t understand some lines in the firmware code involving Timer_A TACCR0 register setting.

Before discussing about Timer_A settings, let me make a preamble.

Preamble.1)
In the file main.c of the source code, the function OSCsel (0x00) let MSP430F2370 do a clock switching from internal DCO clock at 1.1MHz (default DCO frequency at start-up, am I right?) to the external clock source from SYS_CLK pin (pin 27) of TRF7960 on Evaluation Module board. In fact, looking at the EVM schematic, pin 27 of TRF7960 is connected to Xin pin of MSP430F2370.
Nevertheless, the function OSCsel( ) in hardware.c shows these lines :

BCSCTL1 |= XTS + XT2OFF; // ACLK = LFXT1 HF-MODE XTAL
BCSCTL3 |= LFXT1S1; // 3 – 16MHz crystal or resonator
BCSCTL2 |= SELM1 + SELM0 + SELS;

these lines means that ACLK clock is switched from default LFXT1 LF-mode to HF-mode and that LFXT1 clock source is from an external crystal/resonator in 3-16MHz range , and that MCLK = SMCLK = this LFXT1 clock form crystal/resonator : but in the related documents and in the schematic of the TRF7960EVM, wasn’t it said that MCU would operate with the external clock signal of 6,78MHz / 13,56Mhz from TRF7960? Anyway, someone on Texas Instruments forum has told me that the MSP430F2370 will operate well with this external clock from TRF7960 even if the instruction mentioned is BCSCTL3 |= LFXT1S1 instead of BCSCTL3 |= LFXT1S1 + LFXT1S0 as it would have been in my opinion…
What can you tell me about all that I’ve said in this first question?

Preamble. 2)
in main.c , to the function OSCsel ( ) has been passed the value 0x00 , but if another value had been passed, the DCO clock would have been used yet, but with a new value of frequency, as the instructions, in hardware.c, want :
DCOCTL |= DCO0 + DCO1 + DCO2;
BCSCTL1 |= XT2OFF + XTS + RSEL0 + RSEL1 + RSEL2;
So, DCOx = 7 and RSELx = 7 and there isn’t any explanation on MSP430F2370 Data Sheet about how to calculate DCO cloc freq. with this settings… is it in the range of 0,9-3 MHz ?

Preamble. 3)
All along the firmware code, it seems that there isn’t any other clock switch after OSCsel (0x00) in main.c;
This line in main.c : InitialSettings(), calls this routine defined in parallel.c that does set SYS_CLK pin output clock frequency = 6,78MHz

Pramble. 4)
Everytime TimerA is needed, the routine CounterSet ( ) in hardware.c is called : this routine does set for timerA clock source the ACLK clock divided by 8, so, if ACLK = LFXT1 clock = 6,78 MHz , then timerA clock source freq. is 847,5kHz
Everytime it is necessary to start timerA, the macro startCounter is called : this macro is defined in hardware.h on lines 72&73 in 2 ways , but one way as a comment :

line 72 : //#define startCounter TACTL |= MC0 + MC1 //start counter in up/down mode
line 73 : # definestartCounter TACTL |= MC1 //start counter in up mode

in my opinion, the comment in line 73 is wrong, by that instruction we set the “Continuos mode” for timerA not “Up mode” as it should do…
Anyway, let us assume that timerA operates in Up-mode whenever starCounter is found in firmware code.

Preamble is finished :

all along the firmware,the programmer has been used to set, for example to obtain 20ms for Timer_A timeout :

countValue = count1ms * 20;

where countValue is a macro that defines TACCR0 reg. , count1ms is another macro that is a constant value of 847 (decimal value) defined on line 78 of hardware.h
To obtain 20ms of timeout , it is right to set TACCR0 = 847 in my opinion.

countValue = count1ms * 20; can be found on line 127 of anticollision.c file in the Firmware Source Code to obtain 20ms of timeout,and that’s OK; but now, I can’t understand why on line 145 you’ve written :

countValue = 0x4E20;

in my opinion , this new different value for TACCR0 has a sense if , form line 127 to 145 , there has been some ACLK frequency change, and in my opinion there hasn’t been. It’s peculiar that in line 144 you have commented the : countValue = count1ms * 20 instruction : did the programmer change his mind during firmware drawing up? Why?
In my opinion, all along the firmware execution , surely as regards ISO15693 firmware lines execution , but I believe that the same regards other protocols firmware lines implementation, there isn’t any clock changing so I can’t understand,again, why on line 346 of anticollision.c , there is :
countValue = 0xF000;/* 60ms for TIMEOUT */
but then on line 354 : countValue = count1ms * 60; /* 60ms for TIMEOUT */
and this last is the right instruction to obtain 60ms timeout , in my opinion.
Why countValue = 0xF000; has been set for 60ms Timeout?

The same problems I have on : line 152 on epc.c file + line 45,160,171,361,518,615 on 14443.c

I hope you can illuminate me about why isn’t ever used the instruction format :
countValue = count1ms * Y where Y = integer number
that is always right in my opinion.

A last question : the firmware line : __low_power_mode_off_on_exit();
Is it an Interrupt Service Routine (ISR) that switches off any low power mode used in firmware execution whenever an Interrupt is arised to MSP430F2370?
As it seems to me,only LPM0 mode is used in TRF7960EVM firmware, a low power mode that switches off MCLK only, and that doesn’t change SMCLK and ACLK clock frequencies…

Thank you very much for paying attention to me, excuse me for the not-proper English and the “verbosity” of the questions, maybe it’s the only way to let you understand my problems.