Overview

This is a collection of utilities and source to work with assembly for the AX211 SD processor. It consists of an assembler, a utility to kick the processor into code-load mode, and a source file to upload once it's in code-load mode.

Assembler

The assembler originally comes from https://www.pjrc.com/tech/8051/. It is a beta test release. The parser.y file is pre-processed due to Bison not functioning on the current Novena OpenEmbedded distribution.

Utility

The ax211-utility is used for testing the chip. It is also used to load and execute code, and for working with the EIM interface.

For more information, run "./ax211 -h"

ROM File

The ROM file expects to be loaded at offset 0x2900. You're limited to 512 bytes, and you shouldn't assume anything is set up such as a stack.

Using the Interactive Debugger

The ax211 binary now includes an interactive debugger. To run it, you must supply an executable binary. Commands on the host will get transmitted to the card, and the responses will get read back.

The wire protocol is simply a re-purposed SD interface running over two wires. Commands go out the CMD line, and responses come back on the CMD line. You must know how many bytes the response will take, and stop wiggling the clock line once you have reached that many bytes. Be sure to add two bytes, one for the start byte and one for the CRC7.

For information on available commands, run "help".

Debugger Internals

When the debugger starts up, it dumps a small portion of the AX211's RAM and searches for some magical fixup sequences. These three-byte sequences begin with the preamble "0xa5", and are used to overcome some limitations of the 8051, namely with respect to reading from internal RAM.

After it performs fixups, the debugger enters into its main loop. It acts as a shell, and gets its commands from the debug_commands[] array. Each element of the debug_commands array is made up of a struct debug_command:

struct debug_command {
    char    *name;      // Name of the command
    char    *desc;      // Brief, one-line description
    char    *help;      // Multi-line "help" description
    int (*func)(struct dbg *dbg, int argc, char **argv);
};

The func() gets called with a C-style argc and argv, with argv[0] set to the command name. You can call getopt() to process arguments.

Return a negative value upon error. If possible, return a negative errno value, for example -EINVAL or -ENOSPC.