Hi group!
I hope this is the place to discuss code improvement :-)
I've had a look at pata_hard_disk.jal and quickly found some places to
easily increase execution performance.
For example:
--
----------------------------------------------------------------------------
-- Read two bytes from disk.
--
----------------------------------------------------------------------------
procedure pata_hd_read_data(byte out low_byte, byte out high_byte) is
if (pata_hd_word_count == 0) & (pata_hd_sector_count) == 0
then -- if we are at beginning of read
pata_hd_go_to_sector(pata_hd_sector_select,
0) -- go to the selected sector
pata_hd_register_write(PATA_HD_COMMAND_REG,PATA_HD_READ_SECTORS)
-- send the read command to the command
pata_hd_data_request(PATA_HD_WAIT_READ)
-- wait till the drive has data for you
elsif pata_hd_word_count == 0
then -- if we are at beginning of
a sector
pata_hd_data_request(PATA_HD_WAIT_READ)
-- wait for data to be ready for read
end if
"if pata_hd_word_count==0" is checked two times. reducing this to only
one check speeds up (linear) read performance by one third:
procedure pata_hd_read_data(byte out low_byte, byte out high_byte) is
if (pata_hd_word_count == 0) then -- if we are at
beginning of a sector
if (pata_hd_sector_count) == 0
then -- if we are at
beginning of read
pata_hd_go_to_sector(pata_hd_sector_select,
0) -- go to the selected sector
pata_hd_register_write(PATA_HD_COMMAND_REG,PATA_HD_READ_SECTORS)
end
if
-- we are at the beginning of a sector
pata_hd_data_request(PATA_HD_WAIT_READ)
-- wait for data to be ready for read
end if
For read_sector, large_array is nice and convenient, but slow in
execution. PIC18F devices have RAM pages of 256 bytes each, so one
sector can be easily stored in just two ordinary arrays:
var byte pata_hd_sector_buffer_lo[256]
var byte pata_hd_sector_buffer_hi[256]
procedure pata_hd_read_sector() is
var word count1
pata_hd_word_count = 0
[...]
for 256 loop
-- get the data trough the ide interface
pata_hd_iord = high ^ PATA_HD_NO_INVERTER -- start read pulse
pata_hd_sector_buffer_hi[count1] = pata_hd_data_high -- get high
data byte
pata_hd_sector_buffer_lo[count1] = pata_hd_data_low -- get low
data byte
pata_hd_iord = low ^ PATA_HD_NO_INVERTER -- end read pulse
count1 = count1 + 1
end loop
This speeds up reading by more than four times! As the sector buffer
is only used by one procedure yet (fat32.jal / fat32_read_dir_info() )
it may be worth discussing to change the data type of sector_buffer.
Here's an example for an auxiliary function one can use if byte
addressing is desired: (untested)
function pata_hd_sector_buffer_read_linear (word in position) return
byte is
if (position && 1) then -- is an odd memory location requested?
return pata_hd_sector_buffer_hi[position / 2] -- yes, return a
high byte
else
return pata_hd_sector_buffer_lo[position / 2] -- no, return a low
byte
end if
end function
I'm looking forward to any contradiction ;-)
Greets,
Kiste
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