Aerospace Software Requirements

Software Requirements Definition

Software High Level Requirements
From the system requirements, we can help you define high level software requirements. The high level software requirement definition, is the expression of the system requirements specifically to be implemented in code. Each software requirement is systematically traced to a system requirement. Justification is provided for any derived requirements. Software requirements definitions are written by following best practices guidelines.

Software Low Level Requirements
The low level requirements are the expression of the code at the level the closest to the programming language. Each software requirement is systematically traced to a software high level requirement. Software requirements definitions are written by following best practices guidelines. When an automated code generation tool is used the picture is the low level requirement.

DO-178B

The following is a typical example of a fuel metering unit software requirements.

Software High Level Requirements

CL_0000001	SRD 5.2.1:FCU RVDT	TYPE : DRV	SR : R123574
The CL shall read the FCU RVDT Voltage Feedback [OSIN_FCU_RVDT_VFBK] in engineering unit (mV) from the Operating System.

CL_0000002	SRD 5.2.1:FCU RVDT	TYPE : HLR	SR : R123574
The CL shall input the FCU RVDT Voltage Feedback [OSIN_FCU_RVDT_VFBK] into a 2 dimensional map [MAP2D_FCU_RVDT_MV_TO_DEG] to determine the FCU Feedback Angular Position [FCU_RVDT_ANG] in degrees.

CL_0000003	SRD 5.2.1:FCU RVDT	TYPE : HLR	SR : R123574
The CL shall define the 2 dimensional curve (FCU RVDT Voltage Feedback to FCU RVDT Angular Position) [MAP2D_FCU_RVDT_MV_TO_DEG] as per a the following (x,y) points.

CL_0000004	SRD 5.2.1:FCU RVDT	TYPE : DRV	SR : R123574
The CL shall range limit the output of the 2 dimensional curve (FCU RVDT Voltage Feedback to FCU RVDT Angular Position) [MAP2D_FCU_RVDT_MV_TO_DEG] between the minimum y value and maximum y value defined in the map.

CL_0000005	SRD 5.2.7:FCU CONTROL LOOP	TYPE : HLR	SR : R123572
The CL shall calculate the FCU RVDT Position Error [FCU_RVDT_POS_ERR] as per the following equation. FCU Position Error = FCU Position Setpoint - FCU RVDT Angular Position

CL_0000005	SRD 5.2.7:FCU CONTROL LOOP	TYPE : HLR	SR : R123572
The CL shall calculate the FCU RVDT Position Error [FCU_RVDT_POS_ERR] as per the following equation. FCU Position Error = FCU Position Setpoint - FCU RVDT Angular Position

CL_0000006	SRD 5.2.7:FCU CONTROL LOOP	TYPE : HLR	SR : R123572
The CL shall input the FCU Position Error in a Dynamic Filter and output the FCU Torque Motor Current.

CL_0000007	SRD 5.2.7:FCU CONTROL LOOP	TYPE : DRV	SR : R123572
The CL shall use a PID Compensation for the FCU Dynamic Filter.

CL_0000008	SRD 5.2.7:FCU CONTROL LOOP	TYPE : DRV	SR : R123572
The CL shall reset the PID integral gain to 0.0, when the CL is cycled for the first time.

CL_0000010	SRD 5.2.10:FCU FAULT DETECTION	TYPE : DRV	SR : R123579
The CL shall input the FCU RVDT Position Feedback into a first order lag filter with a 200ms time constant.

CL_0000011	SRD 5.2.10:FCU FAULT DETECTION	TYPE : HLR	SR : R123579
The CL shall detect a FCU Position tracking error if the following condition is met : ABS(FCU Position Setpoint-Filtered FCU RVDT Position)>10 degrees

CL_0000012	SRD 5.2.10:FCU FAULT DETECTION	TYPE : HLR	SR : R123579
The CL shall latch a FCU Position Tracking Error Fault when the FCU Position Tracking Error is set for more than 2 sec.

CL_0000013	SRD 5.2.10:FCU FAULT DETECTION	TYPE : HLR	SR : R123580
The CL shall set the FCU Torque Motor Current to 0.0 when a FCU Position Tracking Error Fault is set.

CL_0000014	SRD 5.2.10:FCU FAULT DETECTION	TYPE : DRV	SR : R123580
The CL shall reset the FCU Integral Gain to 0.0 when a FCU Position Tracking Error Fault is set.

CL_0000015	SRD 5.2.15:FCU OUTPUT	TYPE : DRV	SR :
The CL shall output the FCU RVDT Torque Motor Current [OSOUT_FCU_TQCUR] in engineering unit (mV) to the Operating System.


Software Low Level Requirements

SL_0000001	SDD 3.2.1:FCU RVDT	TYPE : LLR	CL : 0000001
The FCU RVDT Voltage Feedback Current Value in engineering unit (mV) [OSIN_FCU_RVDT_VFBK.k] shall be read from the Operating System analog input array IN_OS_ANLG[0].

SL_0000002	SDD 3.2.1:FCU RVDT	TYPE : DRV	CL : 0000001
The FCU RVDT Voltage Feedback Last Past Value in engineering unit (mV) [OSIN_FCU_RVDT_VFBK.k1] shall be equal to its Current Value.

SL_0000003	SDD 3.2.1:FCU RVDT	TYPE : LLR	CL : 0000003
The FCU RVDT Voltage to FCU Angular Position Map [MAP2D_FCU_RVDT_MV_TO_DEG] shall be defined by the following points : MAP2D_FCU_RVDT_MV_TO_DEG.x1=-14.6; MAP2D_FCU_RVDT_MV_TO_DEG.y1=12; MAP2D_FCU_RVDT_MV_TO_DEG.x2=187; MAP2D_FCU_RVDT_MV_TO_DEG.y2=-98;

SL_0000004	SDD 3.2.1:FCU RVDT	TYPE : LLR	CL : 0000002
The FCU RVDT Angular Position in Degree [FCU_RVDT_ANG] shall be calculated using the 2D linear interpolation function linint2dim2ptsfunc that uses the FCU RVDT Position vs Voltage Feedback Map [MAP2D_FCU_RVDT_MV_TO_DEG] for its map input (1st input), and uses the FCU Angular Position [OSIN_FCU_RVDT_VFBK] for its parameter input (2nd input).

SL_0000005	SDD 3.2.1:FCU RVDT	TYPE : LLR	CL : 0000004
The FCU RVDT Angular Position low and high values [RNGLIM_FCU_RVDT_ANG] shall be defined as the minimum and maximum value of thein the for The FCU RVDT Voltage to FCU Angular Position Map [MAP2D_FCU_RVDT_MV_TO_DEG].

SL_0000006	SDD 3.2.1:FCU RVDT	TYPE : LLR	CL : 0000004
The FCU RVDT Angular Position Range Limited [FCU_RVDT_ANG_RNGLIM] shall be calculated using the range limiting function rnglimfunc that uses that uses the FCU RVDT Angular Position low and high values defined in [RNGLIM_FCU_RVDT_ANG] for its range input (1st input), and uses the FCU RVDT Angular Position [FCU_RVDT_ANG_RNGLIM] as its parameter input (2nd input).

SL_0000007	SDD 3.2.1:FCU RVDT	TYPE : LLR	CL : 0000005
The FCU RVDT Position Error [FCU_RVDT_POS_ERR] shall be calculated by substracting the FCU Position Setpoint [FCU_RVDT_SET_POINT] from the FCU RVDT Angular Position [FCU_RVDT_ANG_RGLM].