5.6 AHB Master Status and Interrupts
The Host-I/F accesses the AHB as a bus master. Since the AHB is a multi-master
bus an arbiter grants access to the bus only to one master at a time. In order to
make the status of the AHB transparent to the Host CPU, some information are
provided in form of status information and interrupts.
(1)
AHB master ready
The register bit HOSTSTATUS.AHBMRDY reflects the status of the AHB. If
HOSTSTATUS.AHBMRDY = 0, the AHB is currently occupied, hence any access
to the AHB address space may result in waiting times.
(2)
AHB master overrun interrupt
If a read or write access to the AHB address range is performed while
HOSTSTATUS.AHBMRDY = 0 the AHB master overrun interrupt is activated and
the interrupt flag HOSTINTFLAG.INTIN1 is set. If AHB master overrun interrupt
INT1 is unmasked (HOSTINTENAB.INTEN1 = 1), the Host-I/F interrupt HINT is
asserted.
(3)
AHB master underrun interrupt
If a read access on the Host-I/F is performed and completed before the data is
available the AHB master underrun interrupt is activated and the interrupt flag
HOSTINTFLAG.INTIN0 is set. If AHB master underrun INT0 is unmasked
(HOSTINTENAB.INTEN0 = 1), the Host-I/F interrupt HINT is asserted.
Reason for an AHB master underrun is: the Host CPU reads data too fast from
the Host-I/F.
Beside demanding the Host CPU to guarantee sufficient time between read cycles
possible countermeasures depending on the type of Host-I/F in use:
•
LBus-I/F: the Host CPU can observe the HLBDRQ signal, provided
the data is read in word units
•
ADBus-I/F: the Host CPU should regards the wait signal HADWAIT
(4)
AHB master error interrupt
An AHB master error occurs, if the Host CPU attempts to access an undefined
address range.
Upon occurence of an AHB master error the AHB master error interrupt is
activated and the interrupt flag HOSTINTFLAG.INTIN2 is set. If AHB master error
INT2 is unmasked (HOSTINTENAB.INTEN2 = 1), the Host-I/F interrupt HINT is
asserted.
The AHB master error serves only for debug purpose.
Chapter 5
Host CPU Interface
142
Preliminary User's Manual S19203EE1V3UM00
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