Document number
205065
Version
Rev. N
Issue date
2019-02-04
Sirius OBC and TCM User Manual
Page
120
of
174
bytes, i.e. 16 kbytes, which will be used throughout the document where relevant. The total
amount of mass memory available is 16 Gbytes.
Due to the flash nature of the mass memory, each new block will require erasing before
accepting writes, but the TCM software will handle this automatically. For each 32-bit word
stored in mass memory, there are 8 bits stored as EDAC to be able to detect double errors
and correct single errors. During erases or writes, the operation may fail and the software
will then mark this block as bad and skip this in all future transactions. The bad block list is
stored in NVRAM and will thus survive a reboot and/or power cycling. This graceful
degradation behaviour of the mass memory implies that partitions may shrink in size and
this phenomenon needs to be taken into account when planning partition sizes. Another
effect of the bad blocks is that available space on a partition may decrease by more than the
actual data written and this might need tracking by the user.
To simplify divisions between different types of data with different configurations, the mass
memory is divided into logical partitions where each partition is configured by its mode, type,
segment size and TM virtual channel for downloading. All partitions have an address space
of 4 Gbytes regardless of their physical size and this is also the maximum size of a partition.
Reading and writing to partitions behaves slightly different between different types of
partitions, but when a partition is full, it requires a
free
operation to allow for further writes.
New space for writing will only become available once a block is completely freed (that is,
when a free operation passes over a block boundary).
Figure 7.4 illustrates this with an example two-block partition, showing in the last picture that
new data cannot be written until free has reached the block boundary. To simplify operations
for the user, free operations can be requested on more data than is available in the mass
memory, see 7.12.4.24 for details.
Data written
to mass memory
S
Start of data
E
End of data
E
S
Start
First free
Second free
E
S
E
S
Ready for
write
E
S
Block boundary
Figure 7.4 Illustration of free behaviour and block boundaries.
7.9.1. Partition configuration
Partitions are configured via the NVRAM configuration tool, according to the format in
7.12.4.21, below follows some detailed information regarding certain configuration items.
7.9.1.1. Partition mode
Each partition can be configured as Continuous, Circular or Direct mode.
