Onboard software documentation
==============================
== EEPROM table
Source : link:/documents/SOURCES/mk_romtbl/mk_mea_rom.c[]
=== Energy tables
The MEA software defines 3 energy tables :
- T1 : 128 values [26000, 3] eV
- T2 : 128 values [ 3000, 3] eV
- T3 : 128 values [26000, 3000] eV
The EEPROM table contains 3 energy tables description :
- T1 : 32 ushort values
- T2 : 32 ushort values
- T3 : 32 ushort values
Values are first averaged from 128 to 32 bins, then converted from energy (eV) to velocity (km/s),
and finally converted to ushort and normalized.
----
#define d_Lcl_MEA_2qm 5.931e2 // sqrt (2*q/m) / 1000
#define d_Lcl_MEA_MAX32 1.0273e5 // Normalization parameter (km/s) 30 keV
// sqrt (30000) * d_Lcl_MEA_2qm
#define SIZE 3*32 // 3 tables x 32 values = 96 values
float f_e32 [SIZE]; // 32 energy table values x 3
float f_v32 [SIZE]; // 32 velocity table values x 3
unsigned short us_v32 [SIZE]; // 32 velocity tables normalized ushort x 3
for (i = 0; i < SIZE; i++) {
f_v32 [i] = sqrt (f_e32[i]) * d_Lcl_MEA_2qm;
us_v32 [i] = f_v32[i] / d_Lcl_MEA_MAX32 * 0xffff;
}
----
== Onboard software
=== Global definitions and data structures
Source : link:/documents/SOURCES/Applications/INC/app_MPPE-MEA.h[]
=== Spacecraft potential handling
Source : link:/documents/SOURCES/Applications/APP03/app03_MPPE-MEA.c[]
The part of code below is converting the spacecraft potential value given in global memory variables,
with a couple (A,B) parameters that can be selected by command, and displayed in MEA HK data.
----
#define d_Lcl_MEA_TBL_POT 0x7ff // 2047
double f_potA, f_potB, f_pot;
if (pCtrl->uc_pot_mode) {
index = ?; // Search value of potential for a given TI
if (index < Gd_TRG_MAX)
f_pot = (double) Gs_TRG2_EFD_Pot [index]*d_Lcl_MAX_POT/0x7fff; // Volt
else
f_pot = 0.0;
f_potA = (double) d_Lcl_MEA_MAX_POT *
(pCtl->us_pot_A - d_Lcl_MEA_TBL_POT) / d_Lcl_MEA_TBL_POT;
f_potB = (double) d_Lcl_MEA_MAX_POT *
(pCtl->us_pot_B - d_Lcl_MEA_TBL_POT) / d_Lcl_MEA_TBL_POT;
f_pot = f_potA * f_pot + f_potB; // Volt
}
----
==== Spacecraft potential for 2017/12/15 data
Currently, for the tests during 2017/12/15, the initial values of (A,B) were (2047,2047) that corresponds to (0,0) after normalization.
When entring in spacecraft potential mode for VM calculation, (A,B) becomes (0,2252) that can be converted in :
A = 100 * (0 - 2047) / 2047 = -100
B = 100 * (2252 - 2047) / 2047 = 10.01
So the value in Volt of spacecraft potential is -100 * f_pot + 10.01
With a value of 0.0, it gives -10.01 V
