[i2c,dv] Extend i2c_agent to verify host clock stretching
Host can stretch its clock (scl_o) in case device needs more
time to proceed a received byte. Meaning that, the device
pulls down scl_i after clock cycle 9th then the host can hold
its scl_o at high until the device releases scl_i.
To enable clock stretching feature for the host,
the TIMEOUT_CTRL.EN must be set, and TIMEOUT_CTRL.VAL must
be programmed to a value which is higher than the basic clock pulse.
Once the host clock is stretched longer than the basic clock pulse,
the intr_stretch_timeout_o will be asserted.
Signed-off-by: Tung Hoang <tung.hoang.290780@gmail.com>
diff --git a/hw/dv/sv/i2c_agent/i2c_device_driver.sv b/hw/dv/sv/i2c_agent/i2c_device_driver.sv
index 362880e..fc500d8 100644
--- a/hw/dv/sv/i2c_agent/i2c_device_driver.sv
+++ b/hw/dv/sv/i2c_agent/i2c_device_driver.sv
@@ -11,7 +11,9 @@
constraint rd_data_c { rd_data inside {[0 : 127]}; }
virtual task get_and_drive();
+ int num_stretch_host_clks;
i2c_item rsp_item;
+
@(posedge cfg.vif.rst_ni);
forever begin
cfg.vif.scl_o = 1'b1;
@@ -20,7 +22,23 @@
seq_item_port.get_next_item(rsp_item);
unique case (rsp_item.drv_type)
DevAck: begin
- cfg.vif.device_send_ack(cfg.timing_cfg);
+ fork
+ begin
+ // host clock stretching allows a high-speed host to communicate
+ // with a low-speed device by setting TIMEOUT_CTRL.EN bit
+ // the device ask host clock stretching its clock scl_i by pulling down scl_o
+ // the host clock pulse is extended until device scl_o is pulled up
+ // once scl_o is pulled down longer than TIMEOUT_CTRL.VAL field,
+ // intr_stretch_timeout_o is asserted (ref. https://www.i2c-bus.org/clock-stretching)
+ if (cfg.timing_cfg.enbTimeOut) begin
+ num_stretch_host_clks = gen_num_stretch_host_clks(cfg.timing_cfg);
+ cfg.vif.device_stretch_host_clk(cfg.timing_cfg, num_stretch_host_clks);
+ end
+ end
+ begin
+ cfg.vif.device_send_ack(cfg.timing_cfg);
+ end
+ join
end
RdData: begin
`DV_CHECK_MEMBER_RANDOMIZE_FATAL(rd_data)
@@ -38,5 +56,13 @@
end
endtask : get_and_drive
+ function int gen_num_stretch_host_clks(ref timing_cfg_t tc);
+ // By randomly pulling down scl_o "offset" within [0:2*tc.tTimeOut],
+ // intr_stretch_timeout_o interrupt would be generated uniformly
+ // To test this feature more regressive, there might need a dedicated vseq (V2)
+ // in which TIMEOUT_CTRL.EN is always set.
+ return $urandom_range(tc.tClockPulse, tc.tClockPulse + 2*tc.tTimeOut);
+ endfunction : gen_num_stretch_host_clks
+
endclass : i2c_device_driver
