Data word dropped after PRIM_HOLD

[asmith-kepler]

There appears to be a bug in cont_controller.v when the device sends HOLD. I have attached an ILA trace from that module that illustrates the issue.

This is the response to a COMMAND_DMA_READ_EX (8'h25) command for a single block. Near the end of the frame, the drive sends HOLD, HOLD, data_word, EOF. As you can see from the trace, detect_hold is asserted during the last data word. This causes link_layer_read to discard the last data word. (In sata_stack.v, user_dout_size reports 127 data words instead of 128.)

I have attached a diff against cont_controller.v that I believe fixes the issue: I have modified the assignment to hold_cont by ANDing it with cont_detect. (If HOLD had been followed by CONT, then it would be correct to keep detect_hold asserted during that cycle, but when HOLD is not followed by CONT, then detect_hold should no longer be asserted.) I have changed the other *_cont signals to match because I believe they are likely to behave the same way, although I have not observed a problem with them in practice with the devices I have available for testing.

The device that shows this behaviour is a Samsung 860 EVO SSD. We have also been testing with a Micron M500IT SSD, but we have not seen it issue this pattern of HOLDs. So far, only the Samsung drive has excited this problem.

cont_controller.v.diff.log