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2 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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7 <subtitle>Altos Metrum Operating System</subtitle>
10 <firstname>Keith</firstname>
11 <surname>Packard</surname>
15 <holder>Keith Packard</holder>
19 This document is released under the terms of the
20 <ulink url="http://creativecommons.org/licenses/by-sa/3.0/">
21 Creative Commons ShareAlike 3.0
28 <revnumber>0.1</revnumber>
29 <date>22 November 2010</date>
30 <revremark>Initial content</revremark>
35 <title>Overview</title>
37 AltOS is a operating system built for the 8051-compatible
38 processor found in the TI cc1111 microcontroller. It's designed
39 to be small and easy to program with. The main features are:
42 <para>Multi-tasking. While the 8051 doesn't provide separate
43 address spaces, it's often easier to write code that operates
44 in separate threads instead of tying everything into one giant
49 <para>Non-preemptive. This increases latency for thread
50 switching but reduces the number of places where context
51 switching can occur. It also simplifies the operating system
52 design somewhat. Nothing in the target system (rocket flight
53 control) has tight timing requirements, and so this seems like
54 a reasonable compromise.
58 <para>Sleep/wakeup scheduling. Taken directly from ancient
59 Unix designs, these two provide the fundemental scheduling
60 primitive within AltOS.
64 <para>Mutexes. As a locking primitive, mutexes are easier to
65 use than semaphores, at least in my experience.
69 <para>Timers. Tasks can set an alarm which will abort any
70 pending sleep, allowing operations to time-out instead of
77 The device drivers and other subsystems in AltOS are
78 conventionally enabled by invoking their _init() function from
79 the 'main' function before that calls
80 ao_start_scheduler(). These functions initialize the pin
81 assignments, add various commands to the command processor and
82 may add tasks to the scheduler to handle the device. A typical
83 main program, thus, looks like:
90 /* Turn on the LED until the system is stable */
91 ao_led_init(LEDS_AVAILABLE);
92 ao_led_on(AO_LED_RED);
96 ao_monitor_init(AO_LED_GREEN, TRUE);
97 ao_rssi_init(AO_LED_RED);
99 ao_packet_slave_init();
100 ao_packet_master_init();
105 ao_start_scheduler();
108 As you can see, a long sequence of subsystems are initialized
109 and then the scheduler is started.
113 <title>Programming the 8051 with SDCC</title>
115 The 8051 is a primitive 8-bit processor, designed in the mists
116 of time in as few transistors as possible. The architecture is
117 highly irregular and includes several separate memory
118 spaces. Furthermore, accessing stack variables is slow, and the
119 stack itself is of limited size. While SDCC papers over the
120 instruction set, it is not completely able to hide the memory
121 architecture from the application designer.
124 <title>8051 memory spaces</title>
126 The __data/__xdata/__code memory spaces below were completely
127 separate in the original 8051 design. In the cc1111, this
128 isn't true—they all live in a single unified 64kB address
129 space, and so it's possible to convert any address into a
130 unique 16-bit address. SDCC doesn't know this, and so a
131 'global' address to SDCC consumes 3 bytes of memory, 1 byte as
132 a tag indicating the memory space and 2 bytes of offset within
133 that space. AltOS avoids these 3-byte addresses as much as
134 possible; using them involves a function call per byte
135 access. The result is that nearly every variable declaration
136 is decorated with a memory space identifier which clutters the
137 code but makes the resulting code far smaller and more
141 <title>SDCC 8051 memory spaces</title>
146 The 8051 can directly address these 128 bytes of
147 memory. This makes them precious so they should be
148 reserved for frequently addressed values. Oh, just to
149 confuse things further, the 8 general registers in the
150 CPU are actually stored in this memory space. There are
151 magic instructions to 'bank switch' among 4 banks of
152 these registers located at 0x00 - 0x1F. AltOS uses only
153 the first bank at 0x00 - 0x07, leaving the other 24
154 bytes available for other data.
162 There are an additional 128 bytes of internal memory
163 that share the same address space as __data but which
164 cannot be directly addressed. The stack normally
165 occupies this space and so AltOS doesn't place any
174 This is additional general memory accessed through a
175 single 16-bit address register. The CC1111F32 has 32kB
176 of memory available here. Most program data should live
177 in this memory space.
185 This is an alias for the first 256 bytes of __xdata
186 memory, but uses a shorter addressing mode with
187 single global 8-bit value for the high 8 bits of the
188 address and any of several 8-bit registers for the low 8
189 bits. AltOS uses a few bits of this memory, it should
198 All executable code must live in this address space, but
199 you can stick read-only data here too. It is addressed
200 using the 16-bit address register and special 'code'
201 access opcodes. Anything read-only should live in this space.
209 The 8051 has 128 bits of bit-addressible memory that
210 lives in the __data segment from 0x20 through
211 0x2f. Special instructions access these bits
212 in a single atomic operation. This isn't so much a
213 separate address space as a special addressing mode for
214 a few bytes in the __data segment.
219 <term>__sfr, __sfr16, __sfr32, __sbit</term>
222 Access to physical registers in the device use this mode
223 which declares the variable name, it's type and the
224 address it lives at. No memory is allocated for these
232 <title>Function calls on the 8051</title>
234 Because stack addressing is expensive, and stack space
235 limited, the default function call declaration in SDCC
236 allocates all parameters and local variables in static global
237 memory. Just like fortran. This makes these functions
238 non-reentrant, and also consume space for parameters and
239 locals even when they are not running. The benefit is smaller
240 code and faster execution.
243 <title>__reentrant functions</title>
245 All functions which are re-entrant, either due to recursion
246 or due to a potential context switch while executing, should
247 be marked as __reentrant so that their parameters and local
248 variables get allocated on the stack. This ensures that
249 these values are not overwritten by another invocation of
253 Functions which use significant amounts of space for
254 arguments and/or local variables and which are not often
255 invoked can also be marked as __reentrant. The resulting
256 code will be larger, but the savings in memory are
257 frequently worthwhile.
261 <title>Non __reentrant functions</title>
263 All parameters and locals in non-reentrant functions can
264 have data space decoration so that they are allocated in
265 __xdata, __pdata or __data space as desired. This can avoid
266 consuming __data space for infrequently used variables in
267 frequently used functions.
270 All library functions called by SDCC, including functions
271 for multiplying and dividing large data types, are
272 non-reentrant. Because of this, interrupt handlers must not
273 invoke any library functions, including the multiply and
278 <title>__interrupt functions</title>
280 Interrupt functions are declared with with an __interrupt
281 decoration that includes the interrupt number. SDCC saves
282 and restores all of the registers in these functions and
283 uses the 'reti' instruction at the end so that they operate
284 as stand-alone interrupt handlers. Interrupt functions may
285 call the ao_wakeup function to wake AltOS tasks.
289 <title>__critical functions and statements</title>
291 SDCC has built-in support for suspending interrupts during
292 critical code. Functions marked as __critical will have
293 interrupts suspended for the whole period of
294 execution. Individual statements may also be marked as
295 __critical which blocks interrupts during the execution of
296 that statement. Keeping critical sections as short as
297 possible is key to ensuring that interrupts are handled as
304 <title>Task functions</title>
306 This chapter documents how to create, destroy and schedule AltOS tasks.
309 <title>AltOS Task Functions</title>
311 <term>ao_add_task</term>
315 ao_add_task(__xdata struct ao_task * task,
320 This initializes the statically allocated task structure,
321 assigns a name to it (not used for anything but the task
322 display), and the start address. It does not switch to the
323 new task. 'start' must not ever return; there is no place
336 This terminates the current task.
341 <term>ao_sleep</term>
345 ao_sleep(__xdata void *wchan)
348 This suspends the current task until 'wchan' is signaled
349 by ao_wakeup, or until the timeout, set by ao_alarm,
350 fires. If 'wchan' is signaled, ao_sleep returns 0, otherwise
351 it returns 1. This is the only way to switch to another task.
356 <term>ao_wakeup</term>
360 ao_wakeup(__xdata void *wchan)
363 Wake all tasks blocked on 'wchan'. This makes them
364 available to be run again, but does not actually switch
370 <term>ao_alarm</term>
374 ao_alarm(uint16_t delay)
377 Schedules an alarm to fire in at least 'delay' ticks. If
378 the task is asleep when the alarm fires, it will wakeup
379 and ao_sleep will return 1.
384 <term>ao_wake_task</term>
388 ao_wake_task(__xdata struct ao_task *task)
391 Force a specific task to wake up, independent of which
392 'wchan' it is waiting for.
397 <term>ao_start_scheduler</term>
401 ao_start_scheduler(void)
404 This is called from 'main' when the system is all
405 initialized and ready to run. It will not return.
410 <term>ao_clock_init</term>
417 This turns on the external 48MHz clock then switches the
418 hardware to using it. This is required by many of the
419 internal devices like USB. It should be called by the
420 'main' function first, before initializing any of the
421 other devices in the system.
428 <title>Timer Functions</title>
430 AltOS sets up one of the cc1111 timers to run at 100Hz and
431 exposes this tick as the fundemental unit of time. At each
432 interrupt, AltOS increments the counter, and schedules any tasks
433 waiting for that time to pass, then fires off the ADC system to
434 collect current data readings. Doing this from the ISR ensures
435 that the ADC values are sampled at a regular rate, independent
436 of any scheduling jitter.
439 <title>AltOS Timer Functions</title>
448 Returns the current system tick count. Note that this is
449 only a 16 bit value, and so it wraps every 655.36 seconds.
454 <term>ao_delay</term>
458 ao_delay(uint16_t ticks);
461 Suspend the current task for at least 'ticks' clock units.
466 <term>ao_timer_set_adc_interval</term>
470 ao_timer_set_adc_interval(uint8_t interval);
473 This sets the number of ticks between ADC samples. If set
474 to 0, no ADC samples are generated. AltOS uses this to
475 slow down the ADC sampling rate to save power.
480 <term>ao_timer_init</term>
487 This turns on the 100Hz tick using the CC1111 timer 1. It
488 is required for any of the time-based functions to
489 work. It should be called by 'main' before ao_start_scheduler.
496 <title>AltOS Mutexes</title>
498 AltOS provides mutexes as a basic synchronization primitive. Each
499 mutexes is simply a byte of memory which holds 0 when the mutex
500 is free or the task id of the owning task when the mutex is
501 owned. Mutex calls are checked—attempting to acquire a mutex
502 already held by the current task or releasing a mutex not held
503 by the current task will both cause a panic.
506 <title>Mutex Functions</title>
508 <term>ao_mutex_get</term>
512 ao_mutex_get(__xdata uint8_t *mutex);
515 Acquires the specified mutex, blocking if the mutex is
516 owned by another task.
521 <term>ao_mutex_put</term>
525 ao_mutex_put(__xdata uint8_t *mutex);
528 Releases the specified mutex, waking up all tasks waiting
536 <title>CC1111 DMA engine</title>
538 The CC1111 contains a useful bit of extra hardware in the form
539 of five programmable DMA engines. They can be configured to copy
540 data in memory, or between memory and devices (or even between
541 two devices). AltOS exposes a general interface to this hardware
542 and uses it to handle radio and SPI data.
545 Code using a DMA engine should allocate one at startup
546 time. There is no provision to free them, and if you run out,
547 AltOS will simply panic.
550 During operation, the DMA engine is initialized with the
551 transfer parameters. Then it is started, at which point it
552 awaits a suitable event to start copying data. When copying data
553 from hardware to memory, that trigger event is supplied by the
554 hardware device. When copying data from memory to hardware, the
555 transfer is usually initiated by software.
558 <title>AltOS DMA functions</title>
560 <term>ao_dma_alloc</term>
564 ao_dma_alloc(__xdata uint8_t *done)
567 Allocates a DMA engine, returning the identifier. Whenever
568 this DMA engine completes a transfer. 'done' is cleared
569 when the DMA is started, and then receives the
570 AO_DMA_DONE bit on a successful transfer or the
571 AO_DMA_ABORTED bit if ao_dma_abort was called. Note that
572 it is possible to get both bits if the transfer was
573 aborted after it had finished.
578 <term>ao_dma_set_transfer</term>
582 ao_dma_set_transfer(uint8_t id,
583 void __xdata *srcaddr,
584 void __xdata *dstaddr,
590 Initializes the specified dma engine to copy data
591 from 'srcaddr' to 'dstaddr' for 'count' units. cfg0 and
592 cfg1 are values directly out of the CC1111 documentation
593 and tell the DMA engine what the transfer unit size,
594 direction and step are.
599 <term>ao_dma_start</term>
603 ao_dma_start(uint8_t id);
606 Arm the specified DMA engine and await a signal from
607 either hardware or software to start transferring data.
612 <term>ao_dma_trigger</term>
616 ao_dma_trigger(uint8_t id)
619 Trigger the specified DMA engine to start copying data.
624 <term>ao_dma_abort</term>
628 ao_dma_abort(uint8_t id)
631 Terminate any in-progress DMA transation, marking its
632 'done' variable with the AO_DMA_ABORTED bit.
639 <title>SDCC Stdio interface</title>
641 AltOS offers a stdio interface over both USB and the RF packet
642 link. This provides for control of the device localy or
643 remotely. This is hooked up to the stdio functions in SDCC by
644 providing the standard putchar/getchar/flush functions. These
645 automatically multiplex the two available communication
646 channels; output is always delivered to the channel which
647 provided the most recent input.
650 <title>SDCC stdio functions</title>
659 Delivers a single character to the current console
672 Reads a single character from any of the available
673 console devices. The current console device is set to
674 that which delivered this character. This blocks until
675 a character is available.
687 Flushes the current console device output buffer. Any
688 pending characters will be delivered to the target device.
693 <term>ao_add_stdio</term>
697 ao_add_stdio(char (*pollchar)(void),
698 void (*putchar)(char),
702 This adds another console device to the available
706 'pollchar' returns either an available character or
707 AO_READ_AGAIN if none is available. Significantly, it does
708 not block. The device driver must set 'ao_stdin_ready' to
709 1 and call ao_wakeup(&ao_stdin_ready) when it receives
710 input to tell getchar that more data is available, at
711 which point 'pollchar' will be called again.
714 'putchar' queues a character for output, flushing if the output buffer is
715 full. It may block in this case.
718 'flush' forces the output buffer to be flushed. It may
719 block until the buffer is delivered, but it is not
727 <title>Command line interface</title>
729 AltOS includes a simple command line parser which is hooked up
730 to the stdio interfaces permitting remote control of the device
731 over USB or the RF link as desired. Each command uses a single
732 character to invoke it, the remaining characters on the line are
733 available as parameters to the command.
736 <title>AltOS command line parsing functions</title>
738 <term>ao_cmd_register</term>
742 ao_cmd_register(__code struct ao_cmds *cmds)
745 This registers a set of commands with the command
746 parser. There is a fixed limit on the number of command
747 sets, the system will panic if too many are registered.
748 Each command is defined by a struct ao_cmds entry:
756 'cmd' is the character naming the command. 'func' is the
757 function to invoke and 'help' is a string displayed by the
758 '?' command. Syntax errors found while executing 'func'
759 should be indicated by modifying the global ao_cmd_status
760 variable with one of the following values:
763 <term>ao_cmd_success</term>
766 The command was parsed successfully. There is no
767 need to assign this value, it is the default.
772 <term>ao_cmd_lex_error</term>
775 A token in the line was invalid, such as a number
776 containing invalid characters. The low-level
777 lexing functions already assign this value as needed.
782 <term>ao_syntax_error</term>
785 The command line is invalid for some reason other
795 <term>ao_cmd_lex</term>
802 This gets the next character out of the command line
803 buffer and sticks it into ao_cmd_lex_c. At the end of the
804 line, ao_cmd_lex_c will get a newline ('\n') character.
809 <term>ao_cmd_put16</term>
813 ao_cmd_put16(uint16_t v);
816 Writes 'v' as four hexadecimal characters.
821 <term>ao_cmd_put8</term>
825 ao_cmd_put8(uint8_t v);
828 Writes 'v' as two hexadecimal characters.
833 <term>ao_cmd_white</term>
840 This skips whitespace by calling ao_cmd_lex while
841 ao_cmd_lex_c is either a space or tab. It does not skip
842 any characters if ao_cmd_lex_c already non-white.
847 <term>ao_cmd_hex</term>
854 This reads a 16-bit hexadecimal value from the command
855 line with optional leading whitespace. The resulting value
856 is stored in ao_cmd_lex_i;
861 <term>ao_cmd_decimal</term>
868 This reads a 32-bit decimal value from the command
869 line with optional leading whitespace. The resulting value
870 is stored in ao_cmd_lex_u32 and the low 16 bits are stored
876 <term>ao_match_word</term>
880 ao_match_word(__code char *word)
883 This checks to make sure that 'word' occurs on the command
884 line. It does not skip leading white space. If 'word' is
885 found, then 1 is returned. Otherwise, ao_cmd_status is set to
886 ao_cmd_syntax_error and 0 is returned.
891 <term>ao_cmd_init</term>
898 Initializes the command system, setting up the built-in
899 commands and adding a task to run the command processing
900 loop. It should be called by 'main' before ao_start_scheduler.
907 <title>CC1111 USB target device</title>
909 The CC1111 contains a full-speed USB target device. It can be
910 programmed to offer any kind of USB target, but to simplify
911 interactions with a variety of operating systems, AltOS provides
912 only a single target device profile, that of a USB modem which
913 has native drivers for Linux, Windows and Mac OS X. It would be
914 easy to change the code to provide an alternate target device if
918 To the rest of the system, the USB device looks like a simple
919 two-way byte stream. It can be hooked into the command line
920 interface if desired, offering control of the device over the
921 USB link. Alternatively, the functions can be accessed directly
922 to provide for USB-specific I/O.
925 <title>AltOS USB functions</title>
927 <term>ao_usb_flush</term>
934 Flushes any pending USB output. This queues an 'IN' packet
935 to be delivered to the USB host if there is pending data,
936 or if the last IN packet was full to indicate to the host
937 that there isn't any more pending data available.
942 <term>ao_usb_putchar</term>
946 ao_usb_putchar(char c);
949 If there is a pending 'IN' packet awaiting delivery to the
950 host, this blocks until that has been fetched. Then, this
951 adds a byte to the pending IN packet for delivery to the
952 USB host. If the USB packet is full, this queues the 'IN'
958 <term>ao_usb_pollchar</term>
962 ao_usb_pollchar(void);
965 If there are no characters remaining in the last 'OUT'
966 packet received, this returns AO_READ_AGAIN. Otherwise, it
967 returns the next character, reporting to the host that it
968 is ready for more data when the last character is gone.
973 <term>ao_usb_getchar</term>
977 ao_usb_getchar(void);
980 This uses ao_pollchar to receive the next character,
981 blocking while ao_pollchar returns AO_READ_AGAIN.
986 <term>ao_usb_disable</term>
990 ao_usb_disable(void);
993 This turns off the USB controller. It will no longer
994 respond to host requests, nor return characters. Calling
995 any of the i/o routines while the USB device is disabled
996 is undefined, and likely to break things. Disabling the
997 USB device when not needed saves power.
1000 Note that neither TeleDongle nor TeleMetrum are able to
1001 signal to the USB host that they have disconnected, so
1002 after disabling the USB device, it's likely that the cable
1003 will need to be disconnected and reconnected before it
1009 <term>ao_usb_enable</term>
1013 ao_usb_enable(void);
1016 This turns the USB controller on again after it has been
1017 disabled. See the note above about needing to physically
1018 remove and re-insert the cable to get the host to
1019 re-initialize the USB link.
1024 <term>ao_usb_init</term>
1031 This turns the USB controller on, adds a task to handle
1032 the control end point and adds the usb I/O functions to
1033 the stdio system. Call this from main before
1041 <title>CC1111 Serial peripheral</title>
1043 The CC1111 provides two USART peripherals. AltOS uses one for
1044 asynch serial data, generally to communicate with a GPS device,
1045 and the other for a SPI bus. The UART is configured to operate
1046 in 8-bits, no parity, 1 stop bit framing. The default
1047 configuration has clock settings for 4800, 9600 and 57600 baud
1048 operation. Additional speeds can be added by computing
1049 appropriate clock values.
1052 To prevent loss of data, AltOS provides receive and transmit
1053 fifos of 32 characters each.
1056 <title>AltOS serial functions</title>
1058 <term>ao_serial_getchar</term>
1062 ao_serial_getchar(void);
1065 Returns the next character from the receive fifo, blocking
1066 until a character is received if the fifo is empty.
1071 <term>ao_serial_putchar</term>
1075 ao_serial_putchar(char c);
1078 Adds a character to the transmit fifo, blocking if the
1079 fifo is full. Starts transmitting characters.
1084 <term>ao_serial_drain</term>
1088 ao_serial_drain(void);
1091 Blocks until the transmit fifo is empty. Used internally
1092 when changing serial speeds.
1097 <term>ao_serial_set_speed</term>
1101 ao_serial_set_speed(uint8_t speed);
1104 Changes the serial baud rate to one of
1105 AO_SERIAL_SPEED_4800, AO_SERIAL_SPEED_9600 or
1106 AO_SERIAL_SPEED_57600. This first flushes the transmit
1107 fifo using ao_serial_drain.
1112 <term>ao_serial_init</term>
1116 ao_serial_init(void)
1119 Initializes the serial peripheral. Call this from 'main'
1120 before jumping to ao_start_scheduler. The default speed
1121 setting is AO_SERIAL_SPEED_4800.
1128 <title>CC1111 Radio peripheral</title>
1130 The CC1111 radio transceiver sends and receives digital packets
1131 with forward error correction and detection. The AltOS driver is
1132 fairly specific to the needs of the TeleMetrum and TeleDongle
1133 devices, using it for other tasks may require customization of
1134 the driver itself. There are three basic modes of operation:
1138 Telemetry mode. In this mode, TeleMetrum transmits telemetry
1139 frames at a fixed rate. The frames are of fixed size. This
1140 is strictly a one-way communication from TeleMetrum to
1146 Packet mode. In this mode, the radio is used to create a
1147 reliable duplex byte stream between TeleDongle and
1148 TeleMetrum. This is an asymmetrical protocol with
1149 TeleMetrum only transmitting in response to a packet sent
1150 from TeleDongle. Thus getting data from TeleMetrum to
1151 TeleDongle requires polling. The polling rate is adaptive,
1152 when no data has been received for a while, the rate slows
1153 down. The packets are checked at both ends and invalid
1157 On the TeleMetrum side, the packet link is hooked into the
1158 stdio mechanism, providing an alternate data path for the
1159 command processor. It is enabled when the unit boots up in
1163 On the TeleDongle side, the packet link is enabled with a
1164 command; data from the stdio package is forwarded over the
1165 packet link providing a connection from the USB command
1166 stream to the remote TeleMetrum device.
1171 Radio Direction Finding mode. In this mode, TeleMetrum
1172 constructs a special packet that sounds like an audio tone
1173 when received by a conventional narrow-band FM
1174 receiver. This is designed to provide a beacon to track
1175 the device when other location mechanisms fail.
1181 <title>AltOS radio functions</title>
1183 <term>ao_radio_set_telemetry</term>
1187 ao_radio_set_telemetry(void);
1190 Configures the radio to send or receive telemetry
1191 packets. This includes packet length, modulation scheme and
1192 other RF parameters. It does not include the base frequency
1193 or channel though. Those are set at the time of transmission
1194 or reception, in case the values are changed by the user.
1199 <term>ao_radio_set_packet</term>
1203 ao_radio_set_packet(void);
1206 Configures the radio to send or receive packet data. This
1207 includes packet length, modulation scheme and other RF
1208 parameters. It does not include the base frequency or
1209 channel though. Those are set at the time of transmission or
1210 reception, in case the values are changed by the user.
1215 <term>ao_radio_set_rdf</term>
1219 ao_radio_set_rdf(void);
1222 Configures the radio to send RDF 'packets'. An RDF 'packet'
1223 is a sequence of hex 0x55 bytes sent at a base bit rate of
1224 2kbps using a 5kHz deviation. All of the error correction
1225 and data whitening logic is turned off so that the resulting
1226 modulation is received as a 1kHz tone by a conventional 70cm
1232 <term>ao_radio_idle</term>
1236 ao_radio_idle(void);
1239 Sets the radio device to idle mode, waiting until it reaches
1240 that state. This will terminate any in-progress transmit or
1246 <term>ao_radio_get</term>
1253 Acquires the radio mutex and then configures the radio
1254 frequency using the global radio calibration and channel
1260 <term>ao_radio_put</term>
1267 Releases the radio mutex.
1272 <term>ao_radio_abort</term>
1276 ao_radio_abort(void);
1279 Aborts any transmission or reception process by aborting the
1280 associated DMA object and calling ao_radio_idle to terminate
1281 the radio operation.
1287 <title>AltOS radio telemetry functions</title>
1289 In telemetry mode, you can send or receive a telemetry
1290 packet. The data from receiving a packet also includes the RSSI
1291 and status values supplied by the receiver. These are added
1292 after the telemetry data.
1295 <term>ao_radio_send</term>
1299 ao_radio_send(__xdata struct ao_telemetry *telemetry);
1302 This sends the specific telemetry packet, waiting for the
1303 transmission to complete. The radio must have been set to
1304 telemetry mode. This function calls ao_radio_get() before
1305 sending, and ao_radio_put() afterwards, to correctly
1306 serialize access to the radio device.
1311 <term>ao_radio_recv</term>
1315 ao_radio_recv(__xdata struct ao_radio_recv *radio);
1318 This blocks waiting for a telemetry packet to be received.
1319 The radio must have been set to telemetry mode. This
1320 function calls ao_radio_get() before receiving, and
1321 ao_radio_put() afterwards, to correctly serialize access
1322 to the radio device. This returns non-zero if a packet was
1323 received, or zero if the operation was aborted (from some
1324 other task calling ao_radio_abort()).
1330 <title>AltOS radio direction finding function</title>
1332 In radio direction finding mode, there's just one function to
1336 <term>ao_radio_rdf</term>
1340 ao_radio_rdf(int ms);
1343 This sends an RDF packet lasting for the specified amount
1344 of time. The maximum length is 1020 ms.
1350 <title>Packet mode functions</title>
1352 Packet mode is asymmetrical and is configured at compile time
1353 for either master or slave mode (but not both). The basic I/O
1354 functions look the same at both ends, but the internals are
1355 different, along with the initialization steps.
1358 <term>ao_packet_putchar</term>
1362 ao_packet_putchar(char c);
1365 If the output queue is full, this first blocks waiting for
1366 that data to be delivered. Then, queues a character for
1367 packet transmission. On the master side, this will
1368 transmit a packet if the output buffer is full. On the
1369 slave side, any pending data will be sent the next time
1370 the master polls for data.
1375 <term>ao_packet_pollchar</term>
1379 ao_packet_pollchar(void);
1382 This returns a pending input character if available,
1383 otherwise returns AO_READ_AGAIN. On the master side, if
1384 this empties the buffer, it triggers a poll for more data.
1389 <term>ao_packet_slave_start</term>
1393 ao_packet_slave_start(void);
1396 This is available only on the slave side and starts a task
1397 to listen for packet data.
1402 <term>ao_packet_slave_stop</term>
1406 ao_packet_slave_stop(void);
1409 Disables the packet slave task, stopping the radio receiver.
1414 <term>ao_packet_slave_init</term>
1418 ao_packet_slave_init(void);
1421 Adds the packet stdio functions to the stdio package so
1422 that when packet slave mode is enabled, characters will
1423 get send and received through the stdio functions.
1428 <term>ao_packet_master_init</term>
1432 ao_packet_master_init(void);
1435 Adds the 'p' packet forward command to start packet mode.
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