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$NetBSD: README.port,v 1.4 2006/11/24 22:52:16 wiz Exp $ What to Look for when Porting the IPKDB Interface =============================================== Try to avoid calling any routine from the rest of the kernel. (It's OK to call these routines during initialization). You wouldn't be able to set breakpoints within these routines during debugging, since this would hang the debugging interface. Interface between IPKDB and Ethernet Board (sys/dev/yy/if_xx.c) -------------------------------------------------------------- General Considerations There is a problem when the debugger uses the same ethernet board as does the rest of the kernel. For one thing there might arrive packets destined for the kernel during debugging sessions. These packets are currently lost. For packets on their way out the driver has to leave the interrupt pending condition alone, so the interrupt handler gets a chance to send more packets via the interface. Configuration Files For any interface that may be used for debugging there should be an option, put into opt_ipkdb.h, that is enabled if the kernel shall actually use this interface. The relevant part of the "files" file for interface "xx" would look like this: defopt opt_ipkdb.h IPKDB_XX : IPKDB device xx: ether, ifnet, arp file dev/zz/if_xx.c xx | ipkdb_xx The file dev/zz/if_xx.c contains both the code of the kernel driver and the IPKDB driver for this interface. You should #include "opt_ipkdb.h" in there and conditionalize the compilation of the IPKDB driver with #ifdef IPKDB_XX The appropriate part of the machine configuration would read like this: options IPKDBKEY="\"IPKDB key for remote debugging\"" options IPKDB_XX Driver Code In order to be able to find the debugging interface, the driver has to provide an attach routine that the machine dependent code can call at an appropriate time (see below). The attach routine should take as its first argument a pointer to a struct ipkdb_if plus some additional parameters that allow it to access the devices registers, hopefully using bus_space_* methods. In the ipkdb_if structure, the attach routine must initialize the following fields: myenetaddr fill this with the own ethernet address of the device/machine. flags mark at least IPKDB_MYHW here. name Name of the device, only used for a message. start routine called everytime IPKDB is entered. leave routine called everytime IPKDB is left. receive routine called to receive a packet. send routine called to send a packet. Additional fields that may be set are: myinetaddr fill this with the own internet address, and mark IPKDB_MYIP in flags. port may be used as a pointer to some device dependent data. Unused by other code. The routine should check for existence of the ethernet board. This routine should also note enough information so it is able to later find the system driver instance for the same board in order to coordinate its action with the system driver. The routine should return 0 on success and -1 on failure. The remainder of the routines are called via function pointers in the ipkdb_if structure. The probe routine needs to fill in these function pointers with proper values. void start(struct ipkdb_if *kip) This routine gets called every time the debugger is entered. kip is a pointer to the ipkdb_if structure used for debugging. It should initialize the hardware and software interface. This routine should also note the current state of the board (as far as it can) so a later call to leave can reinstantiate this state. void leave(struct ipkdb_if *kip) This routine is called whenever the debugger is left. It should restore the ethernet hardware to the state prior to the last call to start. int receive(struct ipkdb_if *kip, u_char *buf, int poll) This routine should return an ethernet packet to the buffer pointed to by buf and return its length. The packet should be complete with the ethernet header, i.e. it starts with the recipient address, but does not contain the ethernet checksum. If poll is set, it should return immediately, if no packet is available. Otherwise it should wait for the next packet. This routine shall return the number of bytes transferred to buf. void send(struct ipkdb_if *kip, u_char *buf, int l) This routine should send an ethernet packet out of the debugging interface. The packet is already complete with the ethernet header, but does not contain the ethernet checksum. Interface between IPKDB and Machine (sys/arch/xxx/xxx/ipkdb_glue.c) ----------------------------------------------------------------- void ipkdbinit(void) This routine gets called when the debugger should be entered for the first time. int ipkdb_poll(void) This routine gets called after a panic to check for a keypress by the user. If implemented it allows the user to press any key on the console to do the automatic reboot after a panic. Otherwise the debugging interface will wait forever for some remote debugger to attach in case of a panic. int ipkdbcmds(void) There should be call to this routine from somewhere in locore when the trap mechanism determines that the debugger should be entered, i.e. on a single step or breakpoint interrupt from kernel code. The trapping mechanism should already have stored the registers into the global area ipkdbregs. The layout of this area must be the same as that expected by GDB. The return value of this routine is 0, if the user wants to continue, 1 if the user wants to do single stepping, and 2 if the user has detached from debugging. int ipkdbfbyte(u_char *p) This routine should fetch a byte from address p. It must not enter any trap handling code, but instead return -1 on inability to access the data. void ipkdbsbyte(u_char *p,u_char c) This routine should set the byte pointed to by p to the value given as c. The routine must not enter any trap handling code. Furthermore it should reset the modification bit in the relevant page table entry to the value before the store. sys/arch/xxx/include/ipkdb.h Machine dependent definitions and protoypes should be in sys/arch/xxx/include/ipkdb.h, i.e. in <machine/ipkdb.h>. This includes the size of the array ipkdbregs, that holds the contents of the registers of the debuggee at the time IPKDB is entered.