High-Speed Bus Matrix Slaves
Slave ID
AHB-APB Bridge C
5
SRAM Port 2 - DMAC Data Access
6
11.4.4. SRAM Quality of Service
To ensure that masters with latency requirements get sufficient priority when accessing RAM, priority
levels can be assigned to the masters for different types of access.
The Quality of Service (QoS) level is independently selected for each master accessing the RAM. For any
access to the RAM, the RAM also receives the QoS level. The QoS levels and their corresponding bit
values for the QoS level configuration is shown in the table below.
Table 11-6. Quality of Service
Value
Name
Description
0x0
DISABLE
Background (no sensitive
operation)
0x1
LOW
Sensitive Bandwidth
0x2
MEDIUM
Sensitive Latency
0x3
HIGH
Critical Latency
If a master is configured with QoS level DISABLE (0x0) or LOW (0x1) there will be a minimum latency of
one cycle for the RAM access.
The priority order for concurrent accesses are decided by two factors. First, the QoS level for the master
and second, a static priority given by the port ID. The lowest port ID has the highest static priority. See the
tables below for details.
The MTB has a fixed QoS level HIGH (0x3).
The CPU QoS level can be written/read, using 32-bit access only, at address 0x4100C114, bits [1:0]. Its
reset value is 0x3.
Refer to different master QOSCTRL registers for configuring QoS for the other masters (USB, DMAC).
Table 11-7. SRAM Port Connections QoS
SRAM Port
Connection
Port ID
Connection Type
QoS
default QoS
CM0+ - Cortex
M0+ Processor
0
Bus Matrix
0x4100C114,
bits[1:0]
(1)
0x3
DSU - Device
Service Unit
1
Bus Matrix
0x4100201C,
bits[1:0]
(1)
0x2
DMAC - Direct
Memory Access
Controller - Data
Access
2
Bus Matrix
IP-
QOSCTRL.DQOS
0x2
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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