Texas Instruments TMS320C3x - Manual (Page 197)

Interlocked Operations
7-13 Program Flow Control
7.4 Interlocked Operations
One of the most common parallel processing configurations is the sharing of
global memory by multiple processors. For multiple processors to access this
global memory and share data in a coherent manner, some sort of arbitration
or handshaking is necessary. This requirement for arbitration is the purpose
of the ’C3x interlocked operations.
The ’C3x provides a flexible means of multiprocessor support with five instruc-
tions, referred to as interlocked operations. Through the use of external signals,
these instructions provide powerful synchronization mechanisms. They also
guarantee the integrity of the communication and result in a high-speed opera-
tion. The interlocked-operation instruction group is listed in Table 7–2.
Table 7–2. Interlocked Operations
Mnemonic Description Operation
LDFI Load floating-point value into a register,
interlocked Signal interlocked
src
→
dst
LDII Load integer into a register, interlocked Signal interlocked
src
→
dst
SIGI Signal, interlocked Signal interlocked
Clear interlock
STFI Store floating-point value to memory,
interlocked Clear interlock
src
→
dst
STII Store integer to memory, interlocked Clear interlock
src
→
dst
The interlocked operations use the two external flag pins, XF0 and XF1. XF0
must be configured as an output pin; XF1 is an input pin. When configured in
this manner:
- XF0 signals an interlock operation request
- XF1 acts as an acknowledge signal for the requested interlocked operation.
In this mode, XF0 and XF1 are treated as active-low signals.
The external timing for the interlocked loads and stores is the same as for
standard loads and stores. The interlocked loads and stores may be extended
like standard accesses by using the appropriate ready signal (RDY
int
or
XRDY
int
). (RDY
int
and XRDY
int
are a combination of external ready input and
software wait states. see Chapter 9, External Memory Interface, for more
information on ready generation.)