Use JTAG to invoke offline mode #28
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Previously reconfiguration could fail depending on the JTAG state. For example, `apollo reconfiguration` did not work after `apollo flash-info`.
- Separate implementation from vendor request handler. - Remove redundant board-specific functions.
- Support configuration via both JTAG and SPI flash (or other board-specific method) from the same offline state. - Remove redundant board-specific functions.
This is consistent with the other flash operations.
instead of letting them time out
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This also speeds up several |
mndza
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Oct 11, 2023
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| jtag_init(); | ||
| jtag_go_to_state(STATE_TEST_LOGIC_RESET); | ||
| jtag_wait_time(2); | ||
| jtag_deinit(); |
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What's the purpose of these blocks? Could you add a comment?
Besides that, I think the jtag_go_to_state(STATE_TEST_LOGIC_RESET) is redundant, as this is done implicitly in jtag_init().
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jtag_init() does jtag_set_current_state(STATE_TEST_LOGIC_RESET), not jtag_go_to_state(STATE_TEST_LOGIC_RESET), so it isn't redundant, but perhaps jtag_init() really should call jtag_go_to_state(STATE_TEST_LOGIC_RESET). I've opened #29 to track that as a separate issue.
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From a user's perspective, FPGA configuration state transitions with Apollo currently look like:
(Transient states in blue automatically progress to a subsequent state.)
PROGRAMNpin.(I'm using "offline" and "unconfigured" as names for two separate states because that is what they are called in the code, more or less. Really the FPGA is both offline and unconfigured in both of those states, and the ECP5 documentation uses "offline mode" to refer to even more of the above states.)
Most of the drawbacks of the state machine are due to limitations of the offline and unconfigured modes. It would be desirable to have a single offline mode from which any state transition can be made. After some experimentation I determined that there is no way to support JTAG configuration from offline mode; once the
PROGRAMNpin is pulled low, the only way to get back to user mode is through configuration from flash. It is possible, however, to support all state transitions from unconfigured mode which is invoked by JTAG.This PR consolidates to a single "offline" mode (which is most similar to "unconfigured" mode above). The new state machine looks like:
Most of the complexity in the PR is in firmware which did not previously do JTAG things other than passing through JTAG operations from the host. In my tests it increased the size of the firmware binary by 172 bytes with GCC 10.3.