ARM Software Development Toolkit User Guide 13.7.7. SYS

13.7.7. SYS_READ (0x06)

Read the contents of a file into a buffer. The file position is specified either:

explicitly, by a SYS_SEEK
implicitly, as one byte beyond the previous SYS_READ or SYS_WRITE request.

The file position is at the start of the file when the file is opened, and is lost when the file is closed.The file operation should be performed as a single action whenever possible. That is, a write of 16KB should not be split into four 4KB chunks unless there is no alternative.

Entry

On entry, r1 contains a pointer to a four word data block:

word 1: contains a handle for a file previously opened with SYS_OPEN.
word 2: points to a buffer.
word 3: contains the number of bytes to read to the buffer from the file.
word 4: is an integer that specifies the file mode. Table 13.4 gives the valid values for the integer, and their corresponding ANSI C fopen() modes.

Return

On exit, r0 contains:

0 if the call is successful
the number of bytes not read, if there is an error.

If the handle is for an interactive device (that is, SYS_ISTTY returns –1 for this handle), a non-zero return from SYS_READ indicates that the line read did not fill the buffer.

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