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escc: always set STATUS_TXEMPTY in R_STATUS on device reset

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The "Transmit Interrupts and Transmit Buffer Empty Bit" section of the ESCC
datasheet states the following about the STATUS_TXEMPTY bit: "After a hardware
reset (including a hardware reset by software), or a channel reset, this bit
is set to 1".

Update escc_reset() to set the STATUS_TXEMPTY bit in the R_STATUS register
on device reset as described which fixes a regression whereby the Sun PROM
checks this bit early on startup and gets stuck in an infinite loop if it is
not set.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20211118181835.18497-2-mark.cave-ayland@ilande.co.uk>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Mark Cave-Ayland 2021-11-18 18:18:34 +00:00
parent 8627edfb3f
commit c29cd47e82
1 changed files with 11 additions and 0 deletions
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11
hw/char/escc.c
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@ -354,6 +354,17 @@ static void escc_reset(DeviceState *d)
cs->rregs[j] = 0;
cs->wregs[j] = 0;
}
/*
* ...but there is an exception. The "Transmit Interrupts and Transmit
* Buffer Empty Bit" section on page 50 of the ESCC datasheet says of
* the STATUS_TXEMPTY bit in R_STATUS: "After a hardware reset
* (including a hardware reset by software), or a channel reset, this
* bit is set to 1". The Sun PROM checks this bit early on startup and
* gets stuck in an infinite loop if it is not set.
*/
cs->rregs[R_STATUS] |= STATUS_TXEMPTY;
escc_reset_chn(cs);
}
}