Hi all,

I have a problem resuming block reads on an SDHC card

When the card is being initialised, part of that process is that a PIC
reads the card's FAT and puts copies of the each file's start cluster
and length into two tables. The number of the file to be retrieved is
sent from another PIC. The PIC managing the card fetches its start
cluster and length from the two tables using the file number as an
index. It then gets the blocks from the card under a timer interrupt
until the block count (file length) has been reached. I'm not using
"multiple read.

So far so good

However - if I try to read another file it doesn't work. Only if I
re-initialise the card (which doesn't involve re-reading the FAT)
allows me to access another file. Unfortunately this can take up
to 1/2 second which causes a real hiccup downstream. in the
PIC which uses the data

The documentation I've been using is generally this one

https://www.sdcard.org/downloads/pls/simplified_specs/archive/part1_301.pdf

I haven't found any mention of eg a time-out for data reading and
assumed that CMD17 can be sent any time to access any block

Can anyone offer a clue as to why accessibility of other files seems
to halt at the end of reading another ? I'm sure there's something
I've left out or not doing wuite right. The data from the file read is
fine BTW

TIA

Joe


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