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于 2012年04月27日 23:30, Russell King - ARM Linux 写道:
On Fri, Apr 27, 2012 at 11:18:15AM -0400, Huang Shijie wrote:On Fri, Apr 27, 2012 at 5:50 AM, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote:On Fri, Apr 27, 2012 at 05:46:22PM +0800, Huang Shijie wrote:1. How do you deal with transmitting the high-priority XON/XOFF characters (port->x_char) which occur with s/w flow control and the tty buffers fill up? 2. How do you deal with flow control in general? IOW, what happens when the remote end deasserts your CTS with h/w flow control enabled.If the remote end deasserts my CTS, it means the remote will not send any data. My DMA for RX will expire in the following steps:  the UART only waits for 32 bytes time long  the UART triggers an IDLE Condition Detect DMA.  the dma_rx_callback() will release the DMA for Rx.Err, hang on. I think you're totally confused about hardware flow control. Certainly you're not using the correct terms for what you're describing. The CTS input normally controls the transmitter. In many hardware assisted hardware flow control setups, the deassertion of CTS merely prevents the transmitter starting a new character. This shouldn't have any effect on the receiver of the same UART at all.How does your end deal with sending RTS according to flow control conditions?If a CTS is received after we sent out a RTS, it will follow the steps: imx_int() --> imx_rtsint() --> uart_handle_cts_change() -->start_tx() The start_tx() will create an TX DMA operation, and send out the data.The generation of RTS (connected to the remote ends CTS signal) is supposed to control whether the remote end sends you characters. RTShttp://en.wikipedia.org/wiki/Flow_control#Hardware_flow_control > From the wiki, the generation of RTS (assert by the "master end") is used to send data from the master to slave(the remote), not control the remote end sends me characters.Well, there's a lot of confusion over RTS. Most implementations of it are as per this paragraph on the above page: A non-standard symmetric alternative, commonly called "RTS/CTS handshaking," was developed by various equipment manufacturers. In this scheme, CTS is no longer a response to RTS; instead, CTS indicates permission from the DCE for the DTE to send data to the DCE, and RTS indicates permission from the DTE for the DCE to send data to the DTE. RTS and CTS are controlled by the DTE and DCE respectively, each independent of the other. This was eventually codified in version RS-232-E (actually TIA-232-E by that time) by defining a new signal, "RTR (Ready to Receive)," which is CCITT V.24 circuit 133. TIA-232-E and the corresponding international standards were updated to show that circuit 133, when implemented, shares the same pin as RTS (Request to Send), and that when 133 is in use, RTS is assumed by the DCE to be ON at all times This is what is actually used by all NULL modem cables, serial consoles, and many modems can be (sensibly) configured to support it. Many modems can be configured via AT commands to respond as per the above paragraph too. And this is the hardware flow control scheme implemented by the Linux Kernel for CRTSCTS, plus the hardware assisted hardware flow control provided by industry standard UARTs such as the 1675x and later UARTs.
thanks a lot. I will read the this explanation carefully, and fix my code. Best Regards Huang Shijie -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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