GR712RC-UM, Jun 2017, Version 2.9 206 www.cobham.com/gaisler
GR712RC
27.4 Data Link Protocol Sub-Layer
27.4.1 Physical Channel
The configuration of a Physical Channel covers the following parameters:
• Transfer Frame Length (in number of octets)
• Transfer Frame Version Number
Note that there are other parameters that need to be configured for a Physical Channel, as listed in sec-
tion 27.4.8, covering the All Frame Generation functionality.
The Transfer Frame Length can be programmed by means of the DMA length register.
The Transfer Frame Version Number can be programmed by means of a register, and can take one of
two legal values: 00b for Telemetry and 01b for AOS.
27.4.2 Virtual Channel Frame Service
The Virtual Channel Frame Service is implemented by means of a DMA interface, providing the user
with a means for inserting Transfer Frames into the Telemetry Encoder. Transfer Frames are automat-
ically fetched from memory, for which the user configures a descriptor table with descriptors that
point to each individual Transfer Frame. For each individual Transfer Frame the descriptor also pro-
vides means for bypassing functions in the Telemetry Encoder. This includes the following:
• Virtual Channel Counter generation can be enabled in the Virtual Channel Generation function
(this function is normally only used for Idle Frame generation but can be used for the Virtual
Channel Frame Service when sharing a Virtual Channel)
• Master Channel Counter generation can be bypassed in the Master Channel Generation function
(TM only)
• Frame Secondary Header (FSH) is not supported
• Operational Control Field (OCF) generation can be bypassed in the Master Channel Generation
function (TM only)
• Frame Error Header Control (FECH) generation can be bypassed in the All Frame Generation
function (AOS only)
• Insert Zone (IZ) generation is not supported
• Frame Error Control Field (FECF) generation can be bypassed in the All Frame Generation func-
tion
• A Time Strobe can be generated for the Transfer Frame.
Note that the above features can only be bypassed for each Transfer Frame, the overall enabling of the
features is done for the corresponding functions in the Telemetry Encoder, as described in the subse-
quent sections.
The detailed operation of the DMA interface is described in section 27.8.
27.4.3 Virtual Channel Generation
The Virtual Channel Generation function is used to generate the Virtual Channel Counter for Idle
Frames as described hereafter. The function can however also be enabled for any Transfer Frame
inserted via the Virtual Channel Frame Service described above, allowing a Virtual Channel to be
shared between the two services. In this case the Virtual Channel Counter, the Extended Virtual Chan-
nel Counter (only for TM, as defined for ECSS and PSS, including the complete Transfer Frame Sec-
ondary Header) and the Virtual Channel Counter Cycle (only for AOS) fields will be inserted and
incremented automatically when enabled as described hereafter.
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