Debug - Daisy Chain

About this task

JTAG allows multiple devices to be connected to an interface in a daisy chain configuration. This allows user to use only one debugger to access multiple devices. In a daisy chain, only TMS and TCK signals are common signals which means these signals are required to be routed to all devices on the board. The first device's TDI is connected to the debugger and its TDO is connected to the TDI of the next device. The connection is shown in the following figure.
Figure 1. Daisy Chain Connection of Multiple Devices
In IP Manager, by default, the SoC has a standalone configuration that JTAG cannot access the device which, is outside of SoC. To fix this issue, you need to change the Connection Type to Daisy Chain. Then, specify the number of additional devices in the chain using the option Additional Tap Devices (Max). The total number of devices in the chain should be Additional Tap Devices (Max) + 1. If you select 5 (five) as option for Additional Tap Devices (Max), then you should have a total of up to 6 (six) devices in the chain.
Figure 2. Daisy Chain Parameter Input

After generating the SoC, you need to manually edit the debug launch script to include the device information in the chain. The debug launch script is available in embedded_sw/<soc>/bsp/efinix/EfxSapphireSoc/openocd/debug_<type>.cfg. The debug launch script you select depends on the tap type that is being used on the first device, which is either Trion hardened tap, Titanium hardened tap, or soft tap.

You need to insert information as described:

Procedure

  1. Create a new tap using jtag newtap command to specify other devices in the chain. You need to provide the tap details like IR length, IR capture, and IR mask.
  2. Create a new target if there is Sapphire SoC available with the tap.
    Figure 3. Example 1: Daisy-Chain with 2 Devices
    Example 1: Two devices in the daisy chain, and one of them is running on Sapphire SoC. The debug launch script is:
    set _CHIPNAME fpga_spinal
set _CHIPNAME1 fpga_spinal1
 
#device closest to TDO
jtag newtap $_CHIPNAME bridge -expected-id $_CPUTAPID -irlen <unknown> -ircapture <unknown> -irmask <unknown>
jtag newtap $_CHIPNAME1 bridge -expected-id $_CPUTAPID -irlen <unknown> -ircapture <unknown> -irmask <unknown>
#device closest to TDI
 
target create $_CHIPNAME1.cpu0 vexriscv -endian $_ENDIAN -chain-position $_CHIPNAME1.bridge -coreid 0 -dbgbase 0x10B80000 
vexriscv readWaitCycles 12
vexriscv cpuConfigFile $CPU0_YAML
vexriscv jtagMapping 8 8 0 1 2 2 1 1
  3. Define a name for every device in the chain. Since, there are two devices, give it a name like line 1 and line 2.
  4. Create a new tap with the tap details. In the figure, the device closest to the TDO pin is the device that is without Sapphire SoC and the device closest to the TDI is the device with Sapphire SoC. Refer to the following table and fill the <unknown> with the correct tap details.
    Table 1. Tap Details
    Device IR Length IR Capture IR Mask
    Soft Tap 4 0x1 0xF
  5. Create a new target to specify the Sapphire SoC JTAG mapping details. Refer to the following table to insert the correct JTAG mapping.

Results

Table 2. JTAG Mapping Details
Additional Tap Devices (Max) JTAG Mapping
1 88012211
2 88012222
3 88012233
4 88012244
5 88012255
6 88012266
7 88012277
8 88012288

Figure 4. Example 2: Daisy Chain with 4 Devices

Example 2: Four devices in the daisy chain, and two of them are running on Sapphire SoC. The debug launch script is:

set _CHIPNAME other
set _CHIPNAME1 fpga_spinal1
set _CHIPNAME2 fpga other2
set _CHIPNAME1 fpga_spinal3
 
#device closest to TDO
jtag newtap $_CHIPNAME bridge -irlen <unknown> -ircapture <unknown> -irmask <unknown>
jtag newtap $_CHIPNAME1 bridge -expected-id $_CPUTAPID -irlen <unknown> -ircapture <unknown> -irmask <unknown>
jtag newtap $_CHIPNAME2 bridge -irlen <unknown> -ircapture <unknown> -irmask <unknown>
jtag newtap $_CHIPNAME3 bridge -expected-id $_CPUTAPID -irlen <unknown> -ircapture <unknown> -irmask <unknown>
#device closest to TDI
 
target create $_CHIPNAME1.cpu0 vexriscv -endian $_ENDIAN -chain-position $_CHIPNAME1.bridge -coreid 0 -dbgbase 0x10B80000 
vexriscv readWaitCycles 12
vexriscv cpuConfigFile $CPU0_YAML
vexriscv jtagMapping 8 8 0 1 2 2 3 3

target create $_CHIPNAME3.cpu0 vexriscv -endian $_ENDIAN -chain-position $_CHIPNAME3.bridge -coreid 0 -dbgbase 0x10B80000
vexriscv readWaitCycles 12
vexriscv cpuConfigFile $CPU0_YAML
vexriscv jtagMapping 8 8 0 1 2 2 3 3