On 11/5/26 16:48, Peter Maydell wrote:
Hi; ping for review?
thanks
-- PMM
On Fri, 1 May 2026 at 17:26, Peter Maydell <[email protected]> wrote:
If the guest tries to read more bytes from our fake stub I2C device
than we have provided, we incorrectly read one byte beyond the end of
this array. Avoid this, and instead keep reporting the RXD register
as containing the last byte of the "data transfer".
Having the accelerator data buried in an i2c controller is not good
practice. Anyway good enough for how we use it. Same for this fix:
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Cc: [email protected]
Fixes: 9d68bf564ec ("arm: Stub out NRF51 TWI magnetometer/accelerometer
detection")
Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3408
Signed-off-by: Peter Maydell <[email protected]>
---
hw/i2c/microbit_i2c.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/hw/i2c/microbit_i2c.c b/hw/i2c/microbit_i2c.c
index 2291d6370e..d9689b6f1a 100644
--- a/hw/i2c/microbit_i2c.c
+++ b/hw/i2c/microbit_i2c.c
@@ -41,8 +41,13 @@ static uint64_t microbit_i2c_read(void *opaque, hwaddr addr,
unsigned int size)
data = 0x01;
break;
case NRF51_TWI_REG_RXD:
+ /*
+ * Return the next byte from our fake data sequence. If
+ * the guest keeps reading the register after that, keep
+ * returning the same last byte value.
+ */
data = twi_read_sequence[s->read_idx];
- if (s->read_idx < G_N_ELEMENTS(twi_read_sequence)) {
+ if (s->read_idx + 1 < G_N_ELEMENTS(twi_read_sequence)) {
s->read_idx++;
}
break;
--
