[英]Forth: How to create a word that compiles other words until certain delimiter is found?
我使用Forth(即Swapforth )通過I2C配置某些硬件 。 我有一句話:
i2c1-send ( reg-address byte -- )
將字節寫入特定芯片的特定內部寄存器。 初始化序列很長,因此由於內存消耗,無法按以下方式實現。
: i2c1-init
$1201 $10 i2c1-send
$2130 $43 i2c1-send
[...]
$0231 $43 i2c1-send
;
我創建了一個實現,該實現創建一個結構,該結構在第一個單元格中保留序列的長度,在下一個單元格中保留三字節。 (請注意,i2c1發送只是一個占位符,允許您在沒有我的硬件的情況下對其進行測試)。
: i2c1-send ( reg_addr byte -- )
\ It is just a placeholder to show what will be written in HW
swap
." addr=" hex . ." val=" . decimal CR
;
: i2c1: ( "<spaces>name" -- )
create here $326e9 0 ,
does> dup cell+ swap
@ 0 do
dup c@ >r 1+
dup c@ 8 lshift swap 1+
dup c@ rot or r> i2c1-send
1+
loop
drop
;
: i2c1-def ( addr val -- )
c, ( adr )
dup 8 rshift c,
255 and c,
;
: i2c1; ( -- )
\ Make sure that i2c1: was used before
$326e9 <> abort" i2c1; without i2c1:"
dup cell+ here swap - ( first_cell length )
\ Verify that the length is a multiple of 3
3 /mod swap 0<> abort" illegal length - not a multiple of 3"
swap !
;
使用上面的代碼,您可以類似地定義初始化列表:
i2c1: set1
$1234 $11 i2c1-def
$1521 $18 i2c1-def
[...]
$2313 $10 i2c1-def
i2c1;
但是顯着減少了內存消耗(對於J1B Forth CPU,減少了2倍)。
但是我不喜歡這種語法。 我希望可以通過數字定義初始化列表,直到找到某些定界符為止,如下所示:
i2c1-x: i2c1-init
$1234 $11
$1521 $18
[...]
$2313 $10
i2c1-x;
我創建了如下所示的單詞:
: i2c-delim s" i2c1-x;" ;
: i2c1-x: create here 0 ,
begin
parse-name
2dup i2c-delim compare 0<> while
evaluate \ We store the address later
parse-name
evaluate
c,
\ Now store the address
dup 8 rshift c,
255 and c,
repeat
2drop
dup cell+ here swap - ( first_cell length )
\ Verify that the length is a multiple of 3
3 /mod swap 0<> abort" length not a multiple of 3"
swap !
does> dup cell+ swap
@ 0 do
dup c@ >r 1+
dup c@ 8 lshift swap 1+
dup c@ rot or r> i2c1-send
1+
loop
drop
;
它非常適合簡短定義:
i2c1-x: set2 $1234 $ac $6543 $78 $9871 $01 $3440 $02 i2c1-x;
但是對於使用多行的較長代碼則失敗:
i2c1-x: set2
$1234 $ac
$6543 $78
$9871 $01
$3440 $02
i2c1-x;
是否可以定義i2c1-x
以便處理多行,還是必須使用基於單獨的i2c1:
, i2c1-def
和i2c1;
解決方案i2c1;
?
有REFILL
字來解析多行。
\ Get the next name (lexeme) possibly from the next lines
\ NB: Use the result of parse-name-sure immediate
\ since it may be garbled after the next refill
\ (the buffer may be be overwritten by the next line).
: parse-name-sure ( -- c-addr u|0 )
begin parse-name dup 0= while refill 0= if exit then 2drop repeat
;
\ Check if the first string equals to the second
: equals ( c-addr2 u2 c-addr1 u1 -- flag )
dup 3 pick <> if 2drop 2drop false exit then
compare 0=
;
轉換輸入直到分隔符是一種常見的方法。 執行此方法的一般功能:
\ Translate the input till a delimiter
\ using xt as translator for a lexeme
2variable _delimiter
: translate-input-till-with ( i*x c-addr u xt -- j*x )
>r _delimiter 2!
begin parse-name-sure dup while
2dup _delimiter 2@ equals 0= while
r@ execute
repeat then 2drop rdrop
;
還可以考慮將16位單元的操作納入庫中:
[undefined] w@ [if]
\ NB: little-endian endianness variant
: w! ( x addr -- ) dup 1+ >r >r dup 8 rshift r> c! r> c! ;
: w@ ( addr -- x ) dup c@ 8 lshift swap 1+ c@ or ;
: w, ( x -- ) here 2 allot w! ;
[then]
另外,將文本轉換為數字的功能應該在庫中。 為此使用evaluate
不是衛生的。 請參閱“如何在Forth中輸入數字”問題中的StoN
定義示例。 在您的Forth系統中可以找到轉換“ $”前綴數字的助手。
\ dummy definitions for test only
: s-to-n ( addr u -- x ) evaluate ;
: send-i2c1 ( addr x -- ) ." send: " . . CR ;
應用代碼:
\ Translate the input numbers till the delimiter into the special format
\ (the code could be simplified using the quotations)
: i2c-delim s" i2c1-x;" ;
: translate-i2c-pair ( c-addr u -- )
s-to-n
parse-name-sure
2dup i2c-delim equals abort" translate-i2c: unexpected delimiter"
s-to-n c, w,
;
: translate-i2c-input ( -- )
i2c-delim ['] translate-i2c-pair translate-input-till-with
;
\ Send data from the special format
: send-i2c1-bulk ( addr u -- )
3 / 0 ?do
dup c@ swap 1+
dup w@ swap 2+ >r send-i2c1 r>
loop drop
;
\ The defining word
: i2c1-x:
create here >r 0 , here >r translate-i2c-input here r> - r> !
does> dup cell+ swap @ send-i2c1-bulk
;
一個測試用例
i2c1-x: test
1 2
3 4
5
6
i2c1-x;
test
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