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212 Hardware Reference Manual
Intel
®
IXP2800 Network Processor
SRAM Interface
Up to two Microengine signals are assigned to each read-modify-write reference. Microcode
should always tag the read-modify-write reference with an even-numbered signal. If the operation
requires a pull, the requested signal is sent on the pull. If the pre-modified data is to be returned to
the Microengine, then the Microengine is sent (requested signal OR 1) when that data is pushed.
In Example 28, the version of Test_and_Set requires both a pull and a push:
In Example 29, the version of Test_and_Set does not require a pull, but does issue a push. A signal
is generated when the push is complete.
In Example 30, an Increment operation does not require a pull:
Table 72. Atomic Operations
Instruction Pull Operand Value Written to SRAM
Set_bits Optional
1
1. There are two versions of the Set, Clear, Add, and Swap instructions. One version pulls operand data from the Microengine
transfer registers, and the second version passes the operand data to the SRAM unit as part of the command.
SRAM_Read_Data or Pull_Data
Clear_bits Optional SRAM_Read_Data and not Pull_Data
Increment No SRAM_Read_Data + 0x00000001
Decrement No SRAM_Read_Data - 0x00000001
Add Optional SRAM_Read_Data + Pull_Data
Swap Optional Pull_Data
Example 28. SRAM Test_and_Set with Pull Data
immed [$xfer0, 0x1]
SRAM[test_and_set, $xfer0, test_address, 0, 1], sig_done_2
// SIGNAL_2 is set when $xfer0 is pulled from this ME. SIGNAL_3 is
// set when $xfer0 is written with the test value. Sleep until both
// SIGNALS have arrived.
CTX_ARB[signal_2, signal_3]
Example 29. SRAM Test_and_Set with Optional No-Pull Data
#define no_pull_mode_bit 24
#define byte_mask_override_bit 20
#define no_pull_data_bit 12
#define upper_part_bit 21
// This constant can be created once at init time
ALU[no_pull_constant, --, b, 0x3, <<no_pull_mode_bit]
ALU[no_pull_constant, no_pull_constant, or, 1, <<byte_mask_override_bit]
// Here is a no_pull test_and_add
ALU[temp, no_pull_constant, or, 0xfe, <<no_pull_data_bit]
ALU[temp, temp, or, 0x5, <<upper_part_bit]
SRAM[test_and_add, $x0, addra, 0], indirect_ref, sig_done[sig2]
CTX_ARB[sig2]
Example 30. SRAM Increment without Pull Data
SRAM [incr, $xfer0, incr_address, 0, 1], signal_2
// SIGNAL_2 is set when $xfer0 is written with the pre-increment value.
CTX_ARB[signal_2]