PXE: Difference between revisions

The structure of the PXENV+ structure is as follows:

 

// The Signature of the PXENV+ structure - contains "PXENV+".

uint8_t Signature[6];

// This is a far pointer to the "!PXE" structure, only present when the structure is present.

uint32_t PXEPtr;

 

==== Recommended Usage ====

The structure of the !PXE structure is as follows:

 

// The Signature of the !PXE structure - contains "!PXE".

uint8_t Signature[4];

 

// The rest of the fields don't matter much (in the rest of the article), and the Specifications can be referred.

 

==== Recommended Usage ====

A example generic call function is as follows:

 

; Calls the PXE API, and abstracts things such that it works on both old and new APIs.

; @ds:di The address of the input buffer.

add sp, 6 ; Clean up the stack.

ret

 

The PXE API returns a status flag in AX and the beginning of the input buffer passed. It is recommended to test both of these, where a non zero value indicates failure.

The "t_PXENV_CACHED_INFO" follows the following structure:

 

; Note - due to comfort reasons, the author has decided to provide the following snippet

; in Intel (NASM) Assembly. If someone wishes to change it to a more generic format, he is welcome.

.BufferSeg dw 0

.BufferLimit dw 0

 

* '''.Status'''. This should be zero, and returns the status after the function call.

To do a call, put the address of the above structure in ES:DI, put the opcode, 0x0071, in BX, and call the generic call function. A example call to the above function is, as follows:

 

mov di, t_PXENV_GET_CACHED

mov bx, GET_CACHED_INFO ; 0x0071.

test ax, ax

jnz .Error

 

Bootph has a little complex structure, and the Specification should be referenced to know more about it. For now, the following is what you may require:

PXENV_TFTP_OPEN, with opcode 0x0020 is required to open a file via TFTP. It takes a t_PXENV_TFTP_OPEN structure as a parameter, which has the following format:

 

t_PXENV_TFTP_OPEN:

.Status dw 0

.Port dw 0

.PacketSize dw 0

 

* '''.Status'''. The status word.

The t_PXENV_TFTP_READ has the following structure:

 

t_PXENV_TFTP_READ:

.Status dw 0

.BufferOff dw 0

.BufferSeg dw 0

 

* '''.Status'''. This contains the status returned after the function call.

With the above point in mind, the following pseudo code can be used to read a file:

 

while (bytes_left > 0)

{

bytes_left -= PACKET_SIZE;

}

 

===Closing===

The PXENV_TFTP_CLOSE, with opcode 0x0021, is perhaps the simplest function. It requires a input buffer, with the following format, to be passed to it:

 

t_PXENV_TFTP_CLOSE:

.Status dw 0

 

* '''.Status'''. The Status returned after calling the function. The function would most probably ONLY fail if there is no active TFTP connection.