Ahb Programmable Priority Registers - Samsung S3C2501X User Manual

SYSTEM CONFIGURATION
AHB Bus Programmable Priority Registers are HPRIF(Programmable Priority Register for Fixed) and HPRIR
(Programmable Priority Register for Round-Robin).
If system configuration register (0xF0000000) SYSCFG[0] = 0x1, the programmable fixed priority is run by
HPRIF register. Each master has its own fixed priority index. For example, GDMA has the index 0. The index for
each master is shown in Figure 4-4. The reset value of HPRIF register is 0x00543210. The first field of
HPRIF[3:0] indicates the highest priority and the HPRIF[7:4] indicates the second highest priority and so on.
HPRIF[23:12] should not be writtern any value and must always be 0x543.
The users are allowed to program HPRIF[11:0]. When the SYSCFG[0] = 0x1 and the HPRIF is 0x00543012, the
fixed priority order form the highest to the lowest is Ethernet controller1, ethernet controller0 and General DMA.
If system configuration register (0xF0000000) SYSCFG[0] = 0x0, the programmable round-robin priority is run by
HPRIR register. All AHB bus masters own their respective field position in HPRIR. The ratio of the bus occupancy
can be programmed by writing an arbitrary value on each field. The arbitrary value can be 0x0 to 0xF.
The reset value of HPRIR register is 0x00000000. The position for each master is shown in Figure 4-4.
The ratio of the bus occupancy of the bus master in the first field is intended to be
(hprir0+1)/((hprir2+1)+(hprir1+1)+(hprir0+1)+3) and so on. However, the arbiter of S3C2501X has a fairness
problem.
The HPRIR should be programmed by the value of 0x000330 to have the same occupancy ratio for three
masters.
The arbiter has a problem that the GDMA always has three more chances to occupy the bus than other masters.
Therefore, hprir2 and hprir1 should have the value of (hprir0+3) to keep the same occupancy ratio.
SYSCFG
31
HPRIF
31
HPRIR
31
General DMA (GDMA)
Ethernet Contoller 0
Ethernet Contoller 1
4-6
[0] System bus arbitration method (ARB)
0 = Round-robin
1 = Fixed priority
NOTE: See page 4-16 and 4-17.
Reserved
Low Priority
Reserved
AHB Masters
Figure 4-4. AHB Programmable Priority Registers
12 11
12 11
Index for HPRIF
0
1
2
8 7 4 3
hprif2 hprif1
High Priority
8 7 4 3
hprir2 hprir1
Field for HPRIR
HPRIR[3:0]
HPRIr[7:4]
HPRIR[11:8]
S3C2501X
1 0
x
0
hprif0
0
hprir0