FreeCalypso > hg > freecalypso-sw
comparison gsm-fw/lldbg/README @ 865:f5affe83ba2d
lldbg hack (poor girl's substitute for JTAG) implemented
| author | Space Falcon <falcon@ivan.Harhan.ORG> |
|---|---|
| date | Fri, 15 May 2015 00:02:03 +0000 |
| parents | |
| children |
comparison
equal
deleted
inserted
replaced
| 864:4fa939eada22 | 865:f5affe83ba2d |
|---|---|
| 1 The hack implemented in this directory is a poor girl's substitute for JTAG, | |
| 2 concocted for the purpose of debugging hard crashes in the firmware. The | |
| 3 intended usage is that the developer seeking to troubleshoot perplexing | |
| 4 misbehavior in the firmware inserts a call to lldbg_entry() as a form of | |
| 5 breakpoint at the earliest place in the main fw where it is seen that something | |
| 6 has gone astray, and when the thread of code execution hits this lldbg_entry() | |
| 7 function, the regular Nucleus environment gets completely frozen. Lldbg entry | |
| 8 code saves all registers and the return address (LR) on whatever stack it is | |
| 9 was called on, then disables all interrupts and switches to its own stack which | |
| 10 is not used by any other part of the fw. | |
| 11 | |
| 12 This lldbg code is linked together with the main fw when feature lldbg is | |
| 13 enabled in build.conf, but it stands as its own separate body. All functions | |
| 14 and variables within lldbg are prefixed with lldbg_ to avoid any clashes, and | |
| 15 once this lldbg code gains control, it does everything on its own without making | |
| 16 use of *any* part of the regular fw. The code that forms lldbg is based on | |
| 17 FreeCalypso target-utils (loadagent) and is fully independent of the regular fw. | |
| 18 | |
| 19 Lldbg uses its own UART input and output code as well: the entry code waits for | |
| 20 any previous output (presumably RVTMUX) to go out, then sends out an STX-wrapped | |
| 21 message to make the lldbg entry visible in rvtdump/rvinterf, preceded by 3 STX | |
| 22 characters to terminate any RVTMUX packet in progress. From this point onward | |
| 23 all further communication is done in an ASCII terminal fashion: upon seeing the | |
| 24 lldbg entry message, the user needs to kill rvtdump/rvinterf and switch to | |
| 25 fc-serterm. All lldbg code runs with interrupts disabled, thus UART input and | |
| 26 output are polled. | |
| 27 | |
| 28 Once in lldbg mode, the user (developer) can execute various memory dump | |
| 29 commands to see the frozen state of the fw upon lldbg entry, and hopefully | |
| 30 figure out what went wrong earlier. |