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nrf: fix bug in SPI.Tx

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There was what appears to be a race condition in the Tx function. While
it would work fine in many cases, when there were interrupts (such as
when using BLE), the function would just hang waiting for `EVENTS_READY`
to arrive.

I think what was happening was that the `spi.Bus.RXD.Get()` would start
the next transfer, which would complete (and generate an event) before
`EVENTS_READY` was reset to 0. The fix is easy: clear `EVENTS_READY`
before doing something that can trigger an event.

I believe I've seen this bug before on the PineTime but I couldn't find
the issue back then.
This commit is contained in:
Ayke van Laethem
2020-06-08 16:25:31 +02:00
committed by Ron Evans
parent 9ed5eae6a9
commit 169d5f17b8
1 changed files with 2 additions and 2 deletions
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src/machine/machine_nrf.go
+2 -2
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@@ -443,13 +443,13 @@ func (spi SPI) Tx(w, r []byte) error {
spi.Bus.TXD.Set(uint32(b)) spi.Bus.TXD.Set(uint32(b))
for spi.Bus.EVENTS_READY.Get() == 0 { for spi.Bus.EVENTS_READY.Get() == 0 {
} }
_ = spi.Bus.RXD.Get()
spi.Bus.EVENTS_READY.Set(0) spi.Bus.EVENTS_READY.Set(0)
_ = spi.Bus.RXD.Get()
} }
for spi.Bus.EVENTS_READY.Get() == 0 { for spi.Bus.EVENTS_READY.Get() == 0 {
} }
_ = spi.Bus.RXD.Get()
spi.Bus.EVENTS_READY.Set(0) spi.Bus.EVENTS_READY.Set(0)
_ = spi.Bus.RXD.Get()
default: default:
// write/read // write/read