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1.Packet structure
| -----------less than 512bytes------------ |
| --------------16bytes------------- | ---- |
| -------struct packet_header------- | data |
| --4-- | -4- | --4-- | -2- | --2--- | ---- |
| magic | crc | lenth | cmd | result | data |
(1)MAX_PACKET_LEN now is set to 512 bytes. This can be expanded to 1.5k if necessary.
(2)"magic" is fixed to 0x38316173.
(3)"crc" is the crc32 for *the whole packet*, including the header. When calculating crc32,
	the "crc" value in packet should be set to *0*.
(4)"lenth" is the packet total lenth, including packet header.
(5)"result" is sent from board to pc only.
(6)"cmd" and "data" is shown next.
------------------------------------definition--------------------------------------------------
struct packet_header {
	unsigned int magic;
	unsigned int crc;
	unsigned int lenth; /* total lenth */
	unsigned short cmd;
	unsigned short result;
};
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2.CMD
(1)Commands are separated to 2 parts: simple-cmd(6) and multi-cmd(1).
(2)Multi-cmd means a combination of simple commands, so when (pkt->cmd == CMD_MULT),
	There are several cmds in "data", and needs a new header to show the command info.
	The command header is defined like this:

| magic | crc | lenth | CMD_MULT | result | ---------------------------------command data---------------------------- |
| --------------------------------------- | --------one simple command------ | ... | --------one simple command------ |
| --------------------------------------- | ----------4bytes--------- | ---- | ... | ----------4bytes--------- | ---- |
| --------------------------------------- | -2- | --1-- | -----1----- | ---- | ... | -2- | --1-- | -----1----- | ---- |
| --------------------------------------- | cmd | lenth | is_last = 0 | data | ... | cmd | lenth | is_last = 1 | data |
"cmd" is a simple command.
"lenth" is the total lenth of one command. For example, if "data" is NULL, lenth is 4.
"is_last" indicates if the command is the last command.
"data" is the same as the "data" region in simple command.
(3)simple commands
The simple commands header from pc can be either packet_header or command header,
but board will never send a CMD_MULT to pc, so board only uses packet_header.

"CMD_SYNC" is the sync command used at the first communication.
| ----2--- | 1 | ---1--- |
| CMD_SYNC | 4 | is_last |

"GET_CHIPID" gets the chipid of board. Chipid is a 64-bit value.
pc->board
| ----2----- | 1 | ---1--- |
| GET_CHIPID | 4 | is_last |
board->pc
| --4-- | -4- | 4- | ----2----- | --2--- | --8--- |
| magic | crc | 24 | GET_CHIPID | result | chipid |

"GET_TESTLIST" gets the testlist. Each list name is a 8 bytes string.
pc->board
| ------2----- | 1 | ---1--- |
| GET_TESTLIST | 4 | is_last |
board->pc
| --4-- | -4- | --4-- | ------2----- | --2--- | --------lenth - 16--------- |
| --4-- | -4- | --4-- | ------2----- | --2--- | --8-- | --8-- | ... | --8-- |
| magic | crc | lenth | GET_TESTLIST | result | name1 | name2 | ... | namen |

"DEV_ERASE" is used to erase the last result of pcba-test in dev(flash).
pc->board
| ----2---- | 1- | ---1--- | --4--- | --4-- |
| DEV_ERASE | 12 | is_last | offset | lenth |
board->pc
| --4-- | -4- | 4- | ----2---- | --2--- |
| magic | crc | 16 | DEV_ERASE | result |
"offset" is the flash address, the last 4KB in flash. Command
	"GET_CHIPINFO" can get the ddr and flash total size. For example, for
	16MB flash, offset is 16*1024*1024-4*1024.
"lenth" is the erase lenth.

"DEV_READ" gets the last result of pcba-test in dev(flash).
pc->board
| ----2--- | 1- | ---1--- | --4--- | --4-- |
| DEV_READ | 12 | is_last | offset | lenth |
board->pc
| --4-- | -4- | -----4---- | ----2--- | --2--- | lenth |
| magic | crc | lenth + 16 | DEV_READ | result |  data |
Lenth should be lenth than the max data lenth defined in CMD_MULT "lenth", 256 bytes(8 bit).

"DEV_WRITE" is used to write the result of pcba-test this time into dev.
pc->board
| ----2---- | -----1---- | ---1--- | --4--- | --4-- | lenth |
| DEV_WRITE | lenth + 12 | is_last | offset | lenth |  data |
board->pc
| --4-- | -4- | 4- | ----2---- | --2--- |
| magic | crc | 16 | DEV_WRITE | result |
"data" is the data writen to dev. Board will never analyze the data,
so APP can define it in any format.
Lenth should be lenth than the max data lenth defined in CMD_MULT "lenth", 256 bytes(8 bit).

"RUN_TEST" is the command to start a pcba-test.
pc->board
| ----2--- | ---1-- | ---1--- | ----8---- | -n-- |
| RUN_TEST | 12 + n | is_last | test-name | data |
board->pc
| --4-- | -4- | 4- | ----2--- | --2--- |
| magic | crc | 16 | RUN_TEST | result |
"data" is the case self-defined data.

"GET_CHIPINFO" gets the device info of board. Now device info including ddr and flash size.
pc->board
| -----2------ | 1 | ---1--- |
| GET_CHIPINFO | 4 | is_last |
board->pc
| --4-- | -4- | 4- | ------2----- | --2--- | ---4---- | ----4----- |
| magic | crc | 24 | GET_CHIPINFO | result | ddr_size | flash_size |

(4)command results
Command results are defined in enum values.
CMD_TIMEOUT means the command or test timed out. App can retry the command or test
	on receiving this result.
ERROR_CMD means that the command is not supported or the args for the command are not valid.
CMD_CONTINUE is defined for further use(data lenth > packet max size).

------------------------------------definition--------------------------------------------------
enum cmd_t {
	CMD_SYNC,
	GET_CHIPID,
	GET_TESTLIST,
	DEV_ERASE,
	DEV_READ,
	DEV_WRITE,
	RUN_TEST,
	CMD_MULT,
	GET_CHIPINFO,
};

struct cmd_header {
	unsigned short cmd;
	unsigned char lenth; /* total lenth, less than 256 bytes */
	unsigned char is_last;
};

const struct test_module test_list[] = {
	{ "eth", npu_test }, /* NPU */
	{ "gmac", gmac_test }, /* GMAC */
	{ "wifi", wifi_test }, /* WIFI */
	{ "gpio", gpio_test }, /* GPIO */
	{ "button", button_test }, /* GPIO */
	{ "sd card", sd_test }, /* SDIO */
	{ "usb", usb_test }, /* USB */
	{ "codec", codec_test }, /* PCM/IIS */
	{ "pmu", pmu_test }, /* IIC */
	{ "lcd", lcd_test }, /* GDU */
	{ "spi", spi_test }, /* SPI */
	{ "ddr", ddr_test } /* DDR */
};

enum result_header {
	CMD_FAIL,
	CMD_SUCCESS,
	CMD_CONTINUE,
	CMD_TIMEOUT,
	ERROR_CMD,
};

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3.tests
All tests' board -> pc packet format is the same:
| --4-- | -4- | 4- | ----2--- | --2--- |
| magic | crc | 16 | RUN_TEST | result |

(1)eth test, wifi test, pmu test, sd test, usb test. These tests don't need "data" fields.
pc->board
| ----2--- | 1- | ---1--- | ----8---- |
| RUN_TEST | 12 | is_last | test-name |

(2)led test. Led test will first light all leds for 1 second, then remain only n(0 or 1) leds.
	APP need to send n in "data" field, and the result is a sum of "result" field and the
	tester's choose result.
pc->board
| ----2--- | 1- | ---1--- | ----8---- | --4--- |
| RUN_TEST | 12 | is_last | test-name | 0 or 1 |

(3)button test. Button test don't need "data" field, but the tester must push the reset button
	during the test. APP need to tell the tester to push the button to pass the test. The
	test will return fail after 3 seconds without input.
pc->board
| ----2--- | 1- | ---1--- | ----8---- |
| RUN_TEST | 12 | is_last | test-name |

(4)codec test. Codec test will play one of three sound files. APP needs to tell which file to
	play in "data" field. The sound is the digital "0" "1" "2", corresponding 3 sound files.
	"volume" is the volume of sound, ranges from 0 to 192.
pc->board
| ----2--- | 1- | ---1--- | ----8---- | ----4---- | ---4-- |
| RUN_TEST | 12 | is_last | test-name | 0, 1 or 2 | volume |

(5)lcd test. LCD test will show 3 colors, and then keep at one of them. APP needs to tell which
	color to show and which is the last one in "data" field. The first "color2" is the final
	color shown on lcd. "colorn" value can be 0xff(blue), 0xff00(green), 0xff0000(red).
pc->board
| ----2--- | 1- | ---1--- | ----8---- | --4--- | --4--- | --4--- |
| RUN_TEST | 12 | is_last | test-name | color0 | color1 | color2 |

------------------------------------definition--------------------------------------------------
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