The BBC and Master Computer Public Domain Library
B2C8 SOUND
Submitted by Steve Fewell
Description:
Get the result of the expression at BASIC Text Pointer A and convert the result to Integer (if Float), or issue a
'Type mismatch' error (if String value found).
Set X to 3 (as we have 4 parameters to obtain).
-
Loop for X number of times. For each loop:
- * Push the Integer result (next parameter) LSB 2-bytes (&2A-&2B) to the Stack.
- * Temporarily push X to the stack
- * Check for "," (comma) charater (issue "Missing ," error if not found), and get the Integer result of expression at
BASIC Text pointer B.
- * Retrieve X from the stack.
- * Decrement X value.
- * If X is not 0 yet then loop again.
- * Temporarily push X to the stack
Call routine &9B96 to check that the Statement terminates correctly (if not, then a 'Syntax' error is issued).
Store the last parameter (IWA locations &2A-&2B) in locations &3D-&3E (LSB value (&2A) first).
Set Y to 7 (OSWORD call number for SOUND).
Set X to 5 (Number of parameter bytes left - 1). Each Sound parameter is 2-bytes wide.
Call routine &B307 to do the following:
* Pop the last Byte from the stack and store in location (&37 + X), i.e. location &3C for the MSB of the 3rd SOUND parameter).
* Decrement X and keep repeating from &B307 until X is negative.
* Now location &37 to location &37 + Original X value + 2 (i.e. &3E for SOUND parameter block) contain the
OSWORD call parameters.
* Set A to Y value (the number of the OSWORD call).
* Set X to #&37 and Y to #&00 (as the start of the parameter block is &0037).
* Call the Operating System OSWORD routine (&FFF1) to perform the required operation.
* Jump to &9005 to start processing the next Statement (if any).
Disassembly for the SOUND routine
| B2C8 | o | 032 111 146 | 20 6F 92 | JSR &926F Evaluate Expression at BASIC Text pointer A & convert result to integer |
| B2CB | 162 003 | A2 03 | LDX#&03 | |
| B2CD | * | 165 042 | A5 2A | LDA &2A |
| B2CF | H | 072 | 48 | PHA |
| B2D0 | + | 165 043 | A5 2B | LDA &2B |
| B2D2 | H | 072 | 48 | PHA |
| B2D3 | 218 | DA | PHX | |
| B2D4 | 032 172 150 | 20 AC 96 | JSR &96AC Check for ',', get result of expression and convert result to Integer | |
| B2D7 | 250 | FA | PLX | |
| B2D8 | 202 | CA | DEX | |
| B2D9 | 208 242 | D0 F2 | BNE -14 --> &B2CD | |
| B2DB | 032 150 155 | 20 96 9B | JSR &9B96 Check for end of Statement (PTR B) | |
| B2DE | * | 165 042 | A5 2A | LDA &2A |
| B2E0 | = | 133 061 | 85 3D | STA &3D |
| B2E2 | + | 165 043 | A5 2B | LDA &2B |
| B2E4 | > | 133 062 | 85 3E | STA &3E |
| B2E6 | 160 007 | A0 07 | LDY#&07 | |
| B2E8 | 162 005 | A2 05 | LDX#&05 | |
| B2EA | 128 027 | 80 1B | BRA 27 --> &B307 Create Parameter Block, call OSWORD & process next Statement |
