User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 15: JTAG and Debug Page
435
P
ROCESSOR
AND
P
ROBE
A
CCESS
The JTAG probe can act as both a master and a slave on the ZBbus. As a master, the probe can initiate any
bus transaction. As a slave, the probe responds to accesses in the EJTAG memory range
00_1000_0000
to
00_1001_FFFF
. (This address range will be accessed by the CPU using the alternative debug vector at VA
FFFF_FFFF_B000_0480
.) At any time the probe can either be a master or a slave, however it is possible for
an external debugger to switch between the two modes to support both processor accesses to the probe and
probe accesses to memory.
Probe accesses are controlled by three JTAG registers: the Address Register, the Data Register and the
Control Register. These are described in the subsequent sections. JTAG commands are provided for scanning
these registers individually or as a concatenated chain.
There are two Control Register bits that set the behavior of the probe agent. The ProbEn bit enables accesses
to the EJTAG range and the MaSl bit selects if the probe is a master or a slave.
for the possible cases.
Table 307: CPU and Probe Accesses
ProbEn MaSl
CPU Access to
00_1000_0000 - 00_1001_FFFF
Probe Access to ZBbus
0
0
Probe memory disabled. Read returns zeros, writes
are discarded.
Master mode disabled.
0
1
Probe memory disabled. Read returns zeros, writes
are discarded.
Master mode active. The probe can run ZBbus
cycles.
1
0
Probe memory active. Reads and writes are serviced
by the probe. The EJTAG control register should be
scanned to detect CPU requests.
Master mode disabled.
1
1
Probe accesses delayed. Reads and writes are
blocked and will be serviced when MaSl is set to zero.
Master mode active. The probe can run ZBbus
cycles.
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