diff options
Diffstat (limited to 'common/rtl')
| -rw-r--r-- | common/rtl/clkmgr_dcm.v | 7 | ||||
| -rw-r--r-- | common/rtl/novena_clkmgr.v | 18 |
2 files changed, 16 insertions, 9 deletions
diff --git a/common/rtl/clkmgr_dcm.v b/common/rtl/clkmgr_dcm.v index 5651b93..7c851f1 100644 --- a/common/rtl/clkmgr_dcm.v +++ b/common/rtl/clkmgr_dcm.v @@ -51,13 +51,14 @@ module clkmgr_dcm // // Parameters // - parameter CLK_OUT_MUL = 2; - parameter CLK_OUT_DIV = 2; + parameter CLK_OUT_MUL = 2; // multiply factor for output clock frequency (2..32) + parameter CLK_OUT_DIV = 2; // divide factor for output clock frequency (1..32) // // DCM_SP // + /* Xilinx-specific primitive. */ wire dcm_clk_0; wire dcm_clk_feedback; wire dcm_clk_fx; @@ -121,6 +122,7 @@ module clkmgr_dcm // // Feedback // + /* DCM_SP requires BUFG primitive in its feedback path. */ BUFG BUFG_feedback ( .I (dcm_clk_0), @@ -130,6 +132,7 @@ module clkmgr_dcm // // Output Buffer // + /* Connect system clock to global clocking network. */ BUFG BUFG_output ( .I (dcm_clk_fx), diff --git a/common/rtl/novena_clkmgr.v b/common/rtl/novena_clkmgr.v index 9151e93..e8ef1bd 100644 --- a/common/rtl/novena_clkmgr.v +++ b/common/rtl/novena_clkmgr.v @@ -45,7 +45,7 @@ module novena_clkmgr input wire reset_mcu_b, // cpu reset (async, active-low) output wire sys_clk, // buffered system clock output - output wire sys_rst // system reset output (sync, active-high) + output wire sys_rst_n // system reset output (async set, sync clear, active-low) ); @@ -97,7 +97,8 @@ module novena_clkmgr // /* DCM should be reset on power-up, when input clock is stopped or when the - * CPU gets reset. + * CPU gets reset. Note that DCM requires active-high reset, so the shift + * register is preloaded with 1's and gradually filled with 0's. */ reg [15: 0] dcm_rst_shreg = {16{1'b1}}; // 16-bit shift register @@ -116,18 +117,21 @@ module novena_clkmgr // System Reset Logic // - /* System reset is asserted for 16 cycles whenever DCM aquires lock. */ + /* System reset is asserted for 16 cycles whenever DCM aquires lock. Note + * that system reset is active-low, so the shift register is preloaded with + * 0's and gradually filled with 1's. + */ - reg [15: 0] sys_rst_shreg = {16{1'b1}}; // 16-bit shift register + reg [15: 0] sys_rst_shreg = {16{1'b0}}; // 16-bit shift register always @(posedge sys_clk or negedge reset_mcu_b or posedge gclk_missing or negedge dcm_locked) // if ((reset_mcu_b == 1'b0) || (gclk_missing == 1'b1) || (dcm_locked == 1'b0)) - sys_rst_shreg <= {16{1'b1}}; + sys_rst_shreg <= {16{1'b0}}; else if (dcm_locked == 1'b1) - sys_rst_shreg <= {sys_rst_shreg[14:0], 1'b0}; + sys_rst_shreg <= {sys_rst_shreg[14:0], 1'b1}; - assign sys_rst = sys_rst_shreg[15]; + assign sys_rst_n = sys_rst_shreg[15]; endmodule |