Samsung S5PC100 User Manual page 393

DRAM CONTROLLER
2.5 QUALITY OF SERVICE
QoS is defined for the CONTROLLER as a method to increase the arbitration priority of a master that requires low
latency read data. The QoS is determined if the control queue (Refer to Figure 5.1-1) receives the command
through the AXI bus and the QoS count starts depreciating at this moment. If the count reaches zero, this
command becomes the highest priority among the other commands that are in the control queue.
There are two types of QoS.
• qos_cnt
• default_qos
2.5.1 qos_cnt
There are 8 configurable QoSControls applicable to Read data transfers, which have independent qos_masks that
mask the ARID from one bit up to the ARID width. All 8 QoSControls are either enabled or disabled,
1. If the command is received via the AXI bus, the ARID is masked by the qos_masks
(QoSConfig(n).qos_mask) from the 8 QoSControls that are enabled.
2. The masked results are then compared to the qos_ids (QoSConfig(n).qos_id). If any one of the result are
equal, the qos_cnt (QoSControl(n).qos_cnt) value is applied to the command and saved in the control
queue.
2.5.2 Default QoS
If qos_cnt is not applied to the command, a default QoS counter (Is set to a different value by modifying
ConControl.timeout_cnt) is applied to the command. (Default QoS counter is applied to both read and write)
5.1-10
S5PC100 USER'S MANUAL (REV1.0)