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modem: iface_uart: improve RX flow with HW flow control

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So far all received bytes over UART where blindly drained and pushed to
ring_buf. This approach is okay for UART devices without configured HW
flow control, as it basically decouples data processing from ISR handler
and gives more time before data overrun. However when HW flow control
is enabled, such behavior somehow suppresses UART flow control
advantage, because data can overrun when pushing to ring_buf.

Allow drivers utilizing modem_context framework to pass information
about whether HW flow control is enabled or not. If it is enabled, then
read data from UART FIFO to the point when RX ring_buf is totally filled
and follow such situation by disabling RX interrupt. Incoming data will
be paused on HW level, so there is lots of time for RX thread to process
ring_buf content. Reenable RX interrupts after all data in ring_buf is
processed, so that number of context switches is kept at minimum level.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>
This commit is contained in:
Marcin Niestroj 2020-09-28 21:57:41 +02:00 • committed by Jukka Rissanen
commit 05eb9644dc
2 changed files with 13 additions and 2 deletions
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12
drivers/modem/modem_iface_uart.c
View file

@ -74,8 +74,12 @@ static void modem_iface_uart_isr(const struct device *uart_dev,
UINT32_MAX);
}
if (!partial_size) {
LOG_ERR("Rx buffer doesn't have enough space");
modem_iface_uart_flush(&ctx->iface);
if (data->hw_flow_control) {
uart_irq_rx_disable(ctx->iface.dev);
} else {
LOG_ERR("Rx buffer doesn't have enough space");
modem_iface_uart_flush(&ctx->iface);
}
break;
}
@ -114,6 +118,10 @@ static int modem_iface_uart_read(struct modem_iface *iface,
data = (struct modem_iface_uart_data *)(iface->iface_data);
*bytes_read = ring_buf_get(&data->rx_rb, buf, size);
if (data->hw_flow_control && *bytes_read == 0) {
uart_irq_rx_enable(iface->dev);
}
return 0;
}

3
drivers/modem/modem_iface_uart.h
View file

@ -20,6 +20,9 @@ extern "C" {
#endif
struct modem_iface_uart_data {
/* HW flow control */
bool hw_flow_control;
/* ring buffer char buffer */
char *rx_rb_buf;
size_t rx_rb_buf_len;