Visible to Intel only — GUID: sfo1411572548701
Ixiasoft
Visible to Intel only — GUID: sfo1411572548701
Ixiasoft
7.3.3. JTAG-AP FIFO Buffer Access and Byte Command Protocol
The JTAG-AP contains FIFO buffers for byte commands and responses. The buffers are accessed through the fifosinglebyte, fifodoublebyte, fifotriplebyte, and fifoquadbyte registers. The JTAG-AP stalls processor access to the registers when the buffer does not contain enough data for read access, or when the buffer does not contain enough free space to accept data for write access.
JTAG-AP scan chains 0, 1, 2 and 3 are write-only ports connected to the HPS IOCSRs and JTAG-AP scan chain 7 is a read-write port connected to the FPGA JTAG TAP controller. The processor can send data to scan chains 0-3, and send and receive data from scan chain 7 by accessing the command and response FIFO buffers in the JTAG-AP.
The JTAG commands and TDI data must be sent to the JTAG-AP using an encoded byte protocol. Similarly, the TDO data received from JTAG-AP is encoded. All commands are 8 bits wide in the byte command protocol.
Bits of the Command Byte | Opcode | |||||||
---|---|---|---|---|---|---|---|---|
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
0 | Opcode Payload | TMS | ||||||
1 | 0 | 0 | Opcode Payload | TDI_TDO | ||||
1 | 0 | 1 | X | X | X | X | X | Reserved |
1 | 1 | 0 | X | X | X | X | X | Reserved |
1 | 1 | 1 | X | X | X | X | X | Reserved |