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Fix timing issues in initialization sequence #7

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Fix timing issues in initialization sequence #7

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59e12df
Make sure to wait after issuing slow commands during init sequence
meithecatte Nov 27, 2025
7f0187d
Observe address setup time
meithecatte Nov 27, 2025
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6 changes: 5 additions & 1 deletion src/driver/hd44780/adapter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,9 @@ where
self.send_command_to_controller(controller, LCD_CMD_DISPLAYCONTROL | display_control)?;
self.send_command_to_controller(controller, LCD_CMD_ENTRYMODESET | display_mode)?;
self.send_command_to_controller(controller, LCD_CMD_CLEARDISPLAY)?;
self.device_config().delay.delay_ms(2);
self.send_command_to_controller(controller, LCD_CMD_RETURNHOME)?;
self.device_config().delay.delay_ms(2);
}
// set up the display
self.set_backlight(true)?;
Expand Down Expand Up @@ -143,8 +145,10 @@ where
self.set_rs(rs_setting);
self.set_rw(false);

// now write the low nibble
self.set_data(value & 0x0F);
// first write value without the enable strobe
// to ensure that the address set-up time t_AS = 40 ns is observed
self.write_bits_to_gpio()?;
Comment on lines +149 to +151
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@michaelkamprath michaelkamprath Nov 28, 2025

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Adding the pre-enable write_bits_to_gpio changes every nibble write from two I²C transactions to three, but the mock expectations (e.g. test_generic_hd44780_pcf8574t_init in src/driver/hd44780.rs) still expect two. As written, the test suite will fail and the behavior change isn’t covered. Update the mocks to include the new writes and add a test that captures the t_AS setup write.

Please update the unit tests to reflect your change here.

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@meithecatte meithecatte Nov 28, 2025

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Ah, do you have some kind of automation for updating these tests? I feel like they kind of have the vibe of snapshot tests a la insta...

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@michaelkamprath michaelkamprath Nov 28, 2025

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Run:

cargo test

To see what tests are failing (there are a few), and then figure out why. If you used codex or claude, note that there is a AGENTS.md already in the repo.

self.set_enable(true, controller)?;
self.write_bits_to_gpio()?;
self.set_enable(false, controller)?;
Expand Down