Atmel AT32UC3A3128, Manual

Page: 941 / 1021

941
32072H–AVR32–10/2012
AT32UC3A3
For more information about the SAB and a list of SAB slaves see the Service Access Bus
chapter.
35.4.10.1 SAB Address Mode
The MEMORY_SIZED_ACCESS instruction allows a sized read or write to any 36-bit address
on the bus. MEMORY_WORD_ACCESS is a shorthand instruction for 32-bit accesses to any
36-bit address, while the NEXUS_ACCESS instruction is a Nexus-compliant shorthand instruc-
tion for accessing the 32-bit OCD registers in the 7-bit address space reserved for these. These
instructions require two passes through the Shift-DR TAP state: one for the address and control
information, and one for data.
35.4.10.2 Block Transfer
To increase the transfer rate, consecutive memory accesses can be accomplished by the
MEMORY_BLOCK_ACCESS instruction, which only requires a single pass through Shift-DR for
data transfer only. The address is automatically incremented according to the size of the last
SAB transfer.
35.4.10.3 Canceling a SAB Access
It is possible to abort an ongoing SAB access by the CANCEL_ACCESS instruction, to avoid
hanging the bus due to an extremely slow slave.
35.4.10.4 Busy Reporting
As the time taken to perform an access may vary depending on system activity and current chip
frequency, all the SAB access JTAG instructions can return a busy indicator. This indicates
whether a delay needs to be inserted, or an operation needs to be repeated in order to be suc-
cessful. If a new access is requested while the SAB is busy, the request is ignored.
The SAB becomes busy when:
• Entering Update-DR in the address phase of any read operation, e.g., after scanning in a
NEXUS_ACCESS address with the read bit set.
• Entering Update-DR in the data phase of any write operation, e.g., after scanning in data for
a NEXUS_ACCESS write.
• Entering Update-DR during a MEMORY_BLOCK_ACCESS.
• Entering Update-DR after scanning in a counter value for SYNC.
• Entering Update-IR after scanning in a MEMORY_BLOCK_ACCESS if the previous access
was a read and data was scanned after scanning the address.
The SAB becomes ready again when:
• A read or write operation completes.
• A SYNC countdown completed.
• A operation is cancelled by the CANCEL_ACCESS instruction.
What to do if the busy bit is set:
• During Shift-IR: The new instruction is selected, but the previous operation has not yet
completed and will continue (unless the new instruction is CANCEL_ACCESS). You may
continue shifting the same instruction until the busy bit clears, or start shifting data. If shifting
data, you must be prepared that the data shift may also report busy.
• During Shift-DR of an address: The new address is ignored. The SAB stays in address mode,
so no data must be shifted. Repeat the address until the busy bit clears.