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5 The networking stack in Das U-Boot is designed for multiple network devices
6 to be easily added and controlled at runtime. This guide is meant for people
7 who wish to review the net driver stack with an eye towards implementing your
8 own ethernet device driver. Here we will describe a new pseudo 'APE' driver.
14 All functions you will be implementing in this document have the return value
15 meaning of 0 for success and non-zero for failure.
21 When U-Boot initializes, it will call the common function eth_initialize().
22 This will in turn call the board-specific board_eth_init() (or if that fails,
23 the cpu-specific cpu_eth_init()). These board-specific functions can do random
24 system handling, but ultimately they will call the driver-specific register
25 function which in turn takes care of initializing that particular instance.
27 Keep in mind that you should code the driver to avoid storing state in global
28 data as someone might want to hook up two of the same devices to one board. If
29 the state is maintained as global data, it makes using both of those devices
32 So the call graph at this stage would look something like:
35 board_eth_init() / cpu_eth_init()
40 At this point in time, the only thing you need to worry about is the driver's
41 register function. The pseudo code would look something like:
42 int ape_register(bd_t *bis, int iobase)
44 struct ape_priv *priv;
45 struct eth_device *dev;
47 priv = malloc(sizeof(*priv));
51 dev = malloc(sizeof(*dev));
57 /* setup whatever private state you need */
59 memset(dev, 0, sizeof(*dev));
60 sprintf(dev->name, "APE");
62 /* if your device has dedicated hardware storage for the
63 * MAC, read it and initialize dev->enetaddr with it
65 ape_mac_read(dev->enetaddr);
76 #ifdef CONFIG_CMD_MII)
77 miiphy_register(dev->name, ape_mii_read, ape_mii_write);
83 The exact arguments needed to initialize your device are up to you. If you
84 need to pass more/less arguments, that's fine. You should also add the
85 prototype for your new register function to include/netdev.h. You might notice
86 that many drivers seem to use xxx_initialize() rather than xxx_register().
87 This is the old naming convention and should be avoided as it causes confusion
88 with the driver-specific init function.
90 Other than locating the MAC address in dedicated hardware storage, you should
91 not touch the hardware in anyway. That step is handled in the driver-specific
92 init function. Remember that we are only registering the device here, we are
93 not checking its state or doing random probing.
99 Now that we've registered with the ethernet layer, we can start getting some
100 real work done. You will need four functions:
101 int ape_init(struct eth_device *dev, bd_t *bis);
102 int ape_send(struct eth_device *dev, volatile void *packet, int length);
103 int ape_recv(struct eth_device *dev);
104 int ape_halt(struct eth_device *dev);
106 The init function checks the hardware (probing/identifying) and gets it ready
107 for send/recv operations. You often do things here such as resetting the MAC
108 and/or PHY, and waiting for the link to autonegotiate. You should also take
109 the opportunity to program the device's MAC address with the dev->enetaddr
110 member. This allows the rest of U-Boot to dynamically change the MAC address
111 and have the new settings be respected.
113 The send function does what you think -- transmit the specified packet whose
114 size is specified by length (in bytes). You should not return until the
115 transmission is complete, and you should leave the state such that the send
116 function can be called multiple times in a row.
118 The recv function should process packets as long as the hardware has them
119 readily available before returning. i.e. you should drain the hardware fifo.
120 The common code sets up packet buffers for you already (NetRxPackets), so there
121 is no need to allocate your own. For each packet you receive, you should call
122 the NetReceive() function on it with the packet length. So the pseudo code
123 here would look something like:
124 int ape_recv(struct eth_device *dev)
128 while (packets_are_available()) {
130 length = ape_get_packet(&NetRxPackets[i]);
132 NetReceive(&NetRxPackets[i], length);
134 if (++i >= PKTBUFSRX)
142 The halt function should turn off / disable the hardware and place it back in
145 So the call graph at this stage would look something like:
146 some net operation (ping / tftp / whatever...)
156 -----------------------------
157 CONFIG_MII / CONFIG_CMD_MII
158 -----------------------------
160 If your device supports banging arbitrary values on the MII bus (pretty much
161 every device does), you should add support for the mii command. Doing so is
162 fairly trivial and makes debugging mii issues a lot easier at runtime.
164 After you have called eth_register() in your driver's register function, add
165 a call to miiphy_register() like so:
166 #if defined(CONFIG_MII) || defined(CONFIG_CMD_MII)
167 miiphy_register(dev->name, mii_read, mii_write);
170 And then define the mii_read and mii_write functions if you haven't already.
171 Their syntax is straightforward:
172 int mii_read(char *devname, uchar addr, uchar reg, ushort *val);
173 int mii_write(char *devname, uchar addr, uchar reg, ushort val);
175 The read function should read the register 'reg' from the phy at address 'addr'
176 and store the result in the pointer 'val'. The implementation for the write
177 function should logically follow.