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Hi all,
It's my first query here so I'll try to break a minimum of posting rules.
I have a Embedded programming test for a job application which consists in creating a getTime function. Here is the context :
- a project code is created on a dsPIC33EP512MU814 microcontroller (with a 16MHz quartz) based on an custom API from the company :
This code basically sets up the system and calls on and on a getTime function. Note that the "time" type is uint8 : unsigned char.
- I have a few files from this API ( handling main loop, peripheral includes and type definitions) and the peripherals Library for this microcontroller.
I have to write the getTime time handling function in this API with some constraints :
- time t=0 corresponds to the system powerup
- it's a dating function that can be called a great number of times from project code or peripherals.
- 1us per LSB in resolution
- 100us of maximum dating error between the getTime call and the value return.
- 10h of maximal use of the system.
My problem is that I can't figure out how to respect all these constraints : the resolution forbids the use of the RTC I guess, and using a Timer may not be relevant as we have to count from the powerup. And 10h of system use makes the "time" type too small for this counting
I am not familiar with all the peripherals of this device and I only made a few programs in embedded systems.
I am just looking for a starting point, an idea or a useful ressource I missed somewhere.
Thanks in advance.
It's my first query here so I'll try to break a minimum of posting rules.
I have a Embedded programming test for a job application which consists in creating a getTime function. Here is the context :
- a project code is created on a dsPIC33EP512MU814 microcontroller (with a 16MHz quartz) based on an custom API from the company :
Code:
#include "System.h"
///////////////////////////////////////////////////////////////////////////////////////////////////
// HARDWARE CONFIG
///////////////////////////////////////////////////////////////////////////////////////////////////
// Config hardware boot (mask are only AND defined)
#if defined(__dsPIC33EP512MU810__) || defined(__dsPIC33EP512MU814__)
_FGS(GWRP_OFF & GSS_OFF & GSSK_OFF);
_FOSCSEL(FNOSC_FRC & IESO_ON);
_FOSC(POSCMD_HS & OSCIOFNC_ON & IOL1WAY_OFF & FCKSM_CSECME);
_FWDT(FWDTEN_OFF & WINDIS_OFF & PLLKEN_ON);
_FPOR(FPWRT_PWR1 & BOREN_OFF);
_FICD(ICS_PGD1 & RSTPRI_PF & JTAGEN_OFF);
_FAS(AWRP_OFF & APL_OFF & APLK_OFF);
#else
#error processeur non supporté
#endif
///////////////////////////////////////////////////////////////////////////////////////////////////
// RAM allocation
///////////////////////////////////////////////////////////////////////////////////////////////////
/// structure contenant toutes les variables du système
System sys __attribute__((__near__));
///////////////////////////////////////////////////////////////////////////////////////////////////
// SYSTEM boot
///////////////////////////////////////////////////////////////////////////////////////////////////
int8 systemPowerUp() {
// switch frequency => quartz 16Mhz
PLLFBD = 15 - 2;
CLKDIVbits.PLLPOST = 0;
CLKDIVbits.PLLPRE = 0;
OSCTUN = 0;
RCONbits.SWDTEN = 0;
__builtin_write_OSCCONH(0x03); // Initiate Clock Switch to Primary Oscillator with PLL (XTPLL, HSPLL, ECPLL)
__builtin_write_OSCCONL(0x01); // Start clock switching while (OSCCONbits.COSC != 0b001);
while (OSCCONbits.COSC != 0x03); // Wait for Clock switch to occur
while (OSCCONbits.LOCK != 1);
// Watchdog disabled
RCONbits.SWDTEN = 0;
//enable multi level interrupt
INTCON1bits.NSTDIS = 0;
// disable analog pin
ANSELA = 0;
ANSELB = 0;
ANSELC = 0;
ANSELD = 0;
ANSELE = 0;
ANSELG = 0;
return RETURN_SUCCESS;
}//powerUpSequence
///////////////////////////////////////////////////////////////////////////////////////////////////
// SYSTEM initialisation
///////////////////////////////////////////////////////////////////////////////////////////////////
int8 systemInit() {
return RETURN_SUCCESS;
}//systemInit
///////////////////////////////////////////////////////////////////////////////////////////////////
// SYSTEM starting
///////////////////////////////////////////////////////////////////////////////////////////////////
uint16 cpt;
int8 systemStart() {
cpt = 0;
return RETURN_SUCCESS;
}//systemStart
///////////////////////////////////////////////////////////////////////////////////////////////////
// SYSTEM main loop
///////////////////////////////////////////////////////////////////////////////////////////////////
int8 systemLoop() {
if (!cpt)
{
Time time = getTime();
}
cpt++;
return RETURN_SUCCESS;
}//systemLoop
///////////////////////////////////////////////////////////////////////////////////////////////////
// SYSTEM shutdown
///////////////////////////////////////////////////////////////////////////////////////////////////
int8 systemShutDown() {
return RETURN_SUCCESS;
}//systemShutDown- I have a few files from this API ( handling main loop, peripheral includes and type definitions) and the peripherals Library for this microcontroller.
I have to write the getTime time handling function in this API with some constraints :
- time t=0 corresponds to the system powerup
- it's a dating function that can be called a great number of times from project code or peripherals.
- 1us per LSB in resolution
- 100us of maximum dating error between the getTime call and the value return.
- 10h of maximal use of the system.
My problem is that I can't figure out how to respect all these constraints : the resolution forbids the use of the RTC I guess, and using a Timer may not be relevant as we have to count from the powerup. And 10h of system use makes the "time" type too small for this counting
I am not familiar with all the peripherals of this device and I only made a few programs in embedded systems.
I am just looking for a starting point, an idea or a useful ressource I missed somewhere.
Thanks in advance.
