3.1.4. SYSREF Generator
The SYSREF generator in the design example is used for the duplex JESD204C IP link initialization demonstration purpose only. In the JESD204C subclass 1 system level application,you must generate SYSREF from the same source as the device clock.
For the JESD204C IP, the SYSREF multiplier (SYSREF_MULP) of the SYSREF control register defines the SYSREF period, which is n-integer multiple of the E parameter.
You must ensure E*SYSREF_MULP ≤16. For example, if E=1, the legal setting for SYSREF_MULP must be within 1–16, and if E=3, the legal setting for SYSREF_MULP must be within 1–5.
You can select whether you want the SYSREF type to be a one-shot pulse, periodic, or gapped periodic through the Example Design tab in the JESD204C Intel® FPGA IP parameter editor.
E | SYSREF_MULP | SYSREF PERIOD (E*SYSREF_MULP*16) |
Programmable Duty Cycle | Description |
---|---|---|---|---|
1 | 1 | 16 | 1..15 | Gapped Periodic |
1 | 1 | 16 | Auto (8) | Periodic |
1 | 2 | 32 | 1..31 | Gapped Periodic |
1 | 2 | 32 | 16 | Periodic |
1 | 3 | 48 | 1..47 | Gapped Periodic |
1 | 3 | 48 | Auto (24) | Periodic |
1 | 16 | 256 | 1..255 | Gapped Periodic |
1 | 16 | 256 | Auto (128) | Periodic |
2 | 1 | 32 | 1..31 | Gapped Periodic |
2 | 1 | 32 | 16 | Periodic |
2 | 2 | 64 | 1..31 | Gapped Periodic |
2 | 2 | 64 | Auto (32) | Periodic |
2 | 3 | 96 | 1..95 | Gapped Periodic |
2 | 3 | 96 | Auto (48) | Periodic |
2 | 8 | 256 | 1..255 | Gapped Periodic E*SYSREF_MULP <=16 |
2 | 8 (Illegal<9..16>) |
256 | Auto (128) | Periodic
Note: If you assign an illegal SYSREF_MULP value, the the SYSREF period defaults to 32.
|
16 | 1 Illegal<2..16> |
256 | 1..255 | Gapped Periodic E*SYSREF_MULP <=16 |
Bits | Default Value | Description |
---|---|---|
sysref_ctrl[1:0] |
|
SYSREF type. The default value depends on the SYSREF mode setting in the Example Design tab in the JESD204C Intel® FPGA IP parameter editor. |
sysref_ctrl[6:2] | 5'b00000 | SYSREF multiplier. This SYSREF_MULP field is applicable to periodic and gapped-periodic SYSREF type. You must configure the multiplier value to ensure the E*SYSREF_MULP value is between 1 to 16 before the JESD204C IP is out of reset. If the E*SYSREF_MULP value is out of this range, the multiplier value defaults to 5'b00001. For example: If E =1, write 5'b10000 to sysref_ctrl[6:2] to set the SYSREF_MULP decimal value of 16. |
sysref_ctrl[7] |
|
SYSREF select. The default value depends on the SYSREF mode setting in the Example Design tab in the JESD204C Intel® FPGA IP parameter editor.
|
sysref_ctrl[15:8] | 8'h00 | SYSREF duty cycle when SYSREF type is periodic or gapped periodic. You must configure the duty cycle before the JESD204C IP is out of reset. Maximum value = (E*SYSREF_MULP*16)-1 For example: 50% duty cycle = (E*SYSREF_MULP*16)/2 If you do not configure this register field, the duty cycle defaults to 50%. |
sysref_ctrl[16] | 1'b0 | SYSREF phase (for sysref_out output port).
|
sysref_ctrl[17] | 1'b0 | Manual control when SYSREF type is one-shot.
You need to write a 1 then a 0 to create a SYSREF pulse in one-shot mode. |
sysref_ctrl[31:18] | Don't Care | Reserved. |