CMD_READ/ETD_READ - read sectors of data from a disk.

These commands transfer data from the track buffer to a supplied buffer. If the desired sector is already in the track buffer, no disk activity is initiated. If the desired sector is not in the buffer, the track containing that sector is automatically read in. If the data in the current track buffer has been modified, it is written out to the disk before a new track is read. ETD_READ will read the sector label area if the iotd_SecLabel is non-NULL.

io_Device

preset by the call to OpenDevice()

io_Unit

preset by the call to OpenDevice()

io_Command

CMD_READ or ETD_READ

io_Flags

0 or IOF_QUICK

io_Data

pointer to the buffer where the data should be put

io_Length

number of bytes to read, must be a multiple of TD_SECTOR.

io_Offset

byte offset from the start of the disk describing where to read data from, must be a multiple of TD_SECTOR.

iotd_Count

(ETD_READ only) maximum allowable change counter value.

iotd_SecLabel

(ETD_READ only) NULL or sector label buffer pointer. If provided, the buffer must be a multiple of TD_LABELSIZE.

io_Error

0 for success, or an error code as defined in <devices/trackdisk.h>

Under versions of Kickstart earlier than V36, the io_Data had to point to a buffer in chip memory. This restriction is no longer present as of Kickstart V36 and beyond.

CMD_WRITE