LM3S1G21 Datasheet, PDF (460/955 Pages) Texas Instruments – Stellaris® LM3S1G21 Microcontroller

External Peripheral Interface (EPI)
10.3.1
the offset and size to control the address and size of the external operation. When performing a
multi-value store, the write is done as a burst (when available) to maximize performance.
NAND Flash memory (x8) can be read natively. Automatic programming support is not provided;
programming must be done by the user following the manufacturer's protocol. Automatic page ECC
is also not supported, but can be performed in software.
Non-Blocking Reads
The EPI Controller supports a special kind of read called a non-blocking read, also referred to as a
posted read. Where a normal read stalls the processor or μDMA until the data is returned, a
non-blocking read is performed in the background.
A non-blocking read is configured by writing the start address into a EPIRADDRn register, the size
per transaction into a EPIRSIZEn register, and then the count of operations into a EPIRPSTDn
register. After each read is completed, the result is written into the NBRFIFO and the EPIRADDRn
register is incremented by the size (1, 2, or 4).
If the NBRFIFO is filled, then the reads pause until space is made available. The NBRFIFO can be
configured to interrupt the processor or trigger the μDMA based on fullness using the EPIFIFOLVL
register. By using the trigger/interrupt method, the μDMA (or processor) can keep space available
in the NBRFIFO and allow the reads to continue unimpeded.
When performing non-blocking reads, the SDRAM controller issues two additional read transactions
after the burst request is terminated. The data for these additional transfers is discarded. This
situation is transparent to the user other than the additional EPI bus activity and can safely be
ignored.
Two non-blocking read register sets are available to allow sequencing and ping-pong use. When
one completes, the other then activates. So, for example, if 20 words are to be read from 0x100
and 10 words from 0x200, the EPIRPSTD0 register can be set up with the read from 0x100 (with a
count of 20), and the EPIRPSTD1 register can be set up with the read from 0x200 (with a count of
10). When EPIRPSTD0 finishes (count goes to 0), the EPIRPSTD1 register then starts its operation.
The NBRFIFO has then passed 30 values. When used with the μDMA, it may transfer 30 values
(simple sequence), or the primary/alternate model may be used to handle the first 20 in one way
and the second 10 in another. It is also possible to reload the EPIRPSTD0 register when it is finished
(and the EPIRPSTD1 register is active); thereby, keeping the interface constantly busy.
To cancel a non-blocking read, the EPIRPSTDn register is cleared. Care must be taken, however
if the register set was active to drain away any values read into the NBRFIFO and ensure that any
read in progress is allowed to complete.
To ensure that the cancel is complete, the following algorithm is used (using the EPIRPSTD0 register
for example):
EPIRPSTD0 = 0;
while ((EPISTAT & 0x11) == 0x10)
; // we are active and busy
// if here, then other one is active or interface no longer busy
cnt = (EPIRADDR0 – original_address) / EPIRSIZE0; // count of values read
cnt -= values_read_so_far;
// cnt is now number left in FIFO
while (cnt--)
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January 22, 2012
Texas Instruments-Production Data