The MR25H50 is 512k Bytes or 4 megabits. I consistently confuse MB and mb, similar to Tx/Rx with DB9 connectors.
Do you have any speculation on the memory size of FalconSat-3 based on working with it?
I’ve never seen a published spec.
Jim McCullers
WA4CWI
In the prototype I hold the PACSAT File Headers in memory in a linked list. If we have enough memory to follow the same approach then they would not be read from MRAM except at boot. Each header is about 256 bytes, sometimes shorter. Can be longer. Of course we could read them directly from MRAM but then we would be constantly traversing the MRAM memory every time someone requests a directory listing. We have to scan it to find the entries they want. We could compromise and just hold a linked list of the file-Id a its upload_time in memory. If we will only have enough room in MRAM. That would also avoid duplicating the PACSAT File Header information between MRAM and memory.
When a file is requested we do need to read that from the MRAM, but only a block at a time and at the speed that the downlink can cope with. So that would really minimize the traffic from the MRAM. The same is true for writing. We would only write at the speed we can receive from the uplink. The header is cached in the linked list in memory when it is received, though in the prototype I read it back from the Disk once the file is complete. And I do some lazy things like re-write a whole file rather than seeking the byte offset for the upload time and just updating that. Clearly we would need to do that.
Also, is the MRAM 8 x 512 bits. i.e. 512 bytes? Or its 8 x 512 bytes, so 2MB? Either way, that is not going to be enough to store files where the header alone is 256 bytes. An image might be 65k or more.
To see what I mean, I have attached a copy of this same message (without this last line) as it would be stored on the PACSAT, after upload. It is 1777 bytes.
73
Chris
On Fri, Nov 18, 2022 at 11:03 AM Burns Fisher (AMSAT) <wb1fj@fisher.cc> wrote: